Institut für Kulturpflanzenwissenschaften

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A cropping system for yacon (Smallanthus sonchifolius Poepp. Endl.)
optimizing tuber formation, yield and sugar composition under European conditions
(2020) Kamp, Larissa; Graeff-Hönninger, Simone
The demand of healthy food is constantly increasing in Germany, as well as in developed countries in general. Here "healthy" is not clearly defined but it is often associated with foods indicating a low caloric value and further health-promoting benefits such as a high proportions of dietary fiber, phenols or antioxidants. In contrast, the proportion of obese people and the number of chronic diseases such as diabetes type II and obesity are increasing. As a result, the European Commission recommended to reduce the sugar content and the caloric value of food products, especially in sweetened beverages, breakfast cereals and dairy products by 10%. In general, a distinction can be made between artificial and natural sweeteners. Natural sweeteners such as honey, agave nectar or rapadura occur naturally and do not have to be artificially produced or synthesized. Disadvantages here are the high production costs as well as the high calorie value which is similar to conventionally used sugar. Artificial sweeteners, on the other hand, which are also known as "high-intensity sweeteners", have been artificially produced or synthesized. Examples are aspartame, saccharin or sucralose. They often have a lower calorie value (except for sugar alcohols such as xylitol or sorbitol) and are more economical to produce, which makes them particularly attractive for food producers. However, artificial sweeteners are suspected of being harmful to health or even carcinogenic. As a result, the consumer acceptance of artificial sweeteners is decreasing and the demand for natural sweeteners as alternatives is increasing. A possible alternative as a natural sweetener is yacon (Smallanthus sonchifolius). Yacon is a tuberous root crop native to the Andean region. The roots store carbohydrates mainly as fructooligosaccharides (FOS). These FOS cannot be digested by the human intestinal tract, and therefore do not cause a noticeable increase of blood glucose level. In addition, high amounts of fiber, phenols and antioxidants lead to further health promoting benefits. So far, yacon has been cultivated mainly in the Andean region in smallholder structures. Therefore, there are several open questions regarding the cultivation of yacon in Europe, especially in the area of propagation, choice of genotypes and adapted nitrogen fertilization. Especially the propagation is an important factor, as it is normally done by seedlings of mother plants or single rhizome pieces, both with pre-cultivation in the greenhouse. This is expensive and leads to a price of 3.60 € for young plants. In addition, the influence of genotype and amount of nitrogen fertilization on tuber yield and sugar composition has not been investigated yet. These open questions regarding the cultivation of yacon in Europe outline the following objectives: • to evaluate differences between direct planting and pre cultivation of rhizomes in two ways with regard to yacon growth, development, tuber yield formation and cost distribution; • to investigate the yield potential of different yacon genotypes with regard to tuber yield, sugar yield and tuber composition under the given climatic conditions of Europe; • to determine the influence of different nitrogen levels on nitrogen uptake, tuber yield formation and amount of monosaccharides and polysaccharides as well as total sugar; • to investigate the environmental impact and the production costs of different yacon cultivation systems to determine the most sustainable cultivation method. To achieve the objectives, field trials were carried out a from 2016 to 2018. As a result, four scientific publications were developed, which formed the body of this thesis. Publication I focused on the differences between a propagation with pre-cultivation in the greenhouse (DSAB), rhizome pieces with pre-cultivation in the greenhouse (RP1) and a direct planting of rhizome pieces (RP2) in agronomic and economic terms. RP1 achieved the highest yield with 29.8 t ha 1 FM and differed significantly from the other treatments with 21.3 and 17.8 t ha-1 FM (DSAB and RP2, respectively). With regard to the cost per kg of produced yacon, RP1 was also convincing, which can be explained by a high tuber yield and comparatively low propagation costs. DSAB was the most expensive treatment and is therefore not recommended. Contrary to that RP2 has a high potential for mechanization and yield increases. Publication II investigated the differences between nine different genotypes with respect to tuber yield and sugar composition. The three genotypes red-shelled, brown-shelled and Morado achieved the significantly highest tuber yields with 46.6, 43.5 and 41.6 t FM ha-1. Also the sugar contents were outstanding with up to 66% of the DM in the red-shelled genotype. As a result, the sugar yields of these three genotypes were highest with 2.2, 2.0 and 1.9 t ha-1 in the same order as the tuber yields. In Publication III the influence of different amounts of nitrogen fertilizer (0, 40 and 80 kg ha-1) on tuber yield, sugar composition and nitrogen uptake of the brown- and red-shelled genotype was investigated. Both genotypes reached highest tuber yields of 50 and 67 t FM ha-1 at the highest nitrogen fertilizer amount (brown- and red-shelled, respectively). Contrary to this responded the total amounts of sugar and FOS. Both decreased with increasing amounts of nitrogen. With decreasing amounts of FOS, the proportion of FOS with higher degree of polymerization (DP) increased. With regard to the nitrogen utilization efficiency of both, tubers and the entire plant, a nitrogen amount of 40 kg N ha-1 seems to be sufficient and recommendable. Publication IV examined the ecological and economic sustainability of the cultivation of two genotypes (brown- and red-shelled), each with pre-cultivation in the greenhouse and as direct planting, with three different nitrogen fertilizer levels. The aim was to investigate the environmental impact and production costs of different yacon cultivation systems. Considering the costs, the highest fertilizer amount (80 kg N ha-1) led to the lowest production costs and also to comparatively low environmental impacts per functional unit (1 kg FOS). The red-shelled genotype performed better, both in terms of cost and environmental impact. This was mainly due to higher tuber yields. Overall, the preceding publications showed that the cultivation of yacon in Europe is possible and offers new possibilities for farmers. Embedding yacon successfully into existing cropping systems and crop rotations seems to be possible. The farmer has the opportunity to establish a promising new crop with great value potential on his farm in order to cover the increasing demand for raw materials for natural sweeteners.
Agricultural diversification of biogas crop cultivation
(2018) von Cossel, Moritz; Lewandowski, Iris
For all types of agricultural land-use, more diverse cropping systems are required, with respect to the maintenance of ecosystem values such as biodiversity conservation and climate change adaptation. This need for greater agricultural diversity is clearly illustrated by biogas crop cultivation. In Germany, maize currently dominates biogas crop cultivation due to its outstanding methane yield performance. However, the ecosystem value of maize cultivation decreases if good agricultural practices are ignored. Additionally, the poor aesthetical value of maize has led to biogas production gaining a negative reputation in society. To increase the diversity of biogas crop cultivation, alternative biogas crops such as amaranth and wild plant mixtures need to be investigated with respect to both yield performance and biogas substrate quality. The research objective of this study was the development of strategies for agricultural diversification of biogas crop cultivation. For this purpose, the following research questions were formulated: 1. How does amaranth perform as a biogas crop compared to maize and what are the major opportunities for and obstacles to the large-scale implementation of amaranth cultivation? 2. How does the spatial diversification ‘legume intercropping’ perform in amaranth compared to maize and what are the major opportunities for and obstacles to its practical implementation? 3. How do perennial wild plant mixtures perform in biomass production with respect to yield, quality and species diversity in the long term and what are the relevant agronomic factors? 4. How do available models perform in the prediction of specific methane yield of different crops based on their lignocellulosic biomass composition and how could they be improved? To address research questions 1 and 2, field trials with amaranth and maize were conducted in southwest Germany in the years 2014 and 2015. Amaranth established well in both years. Its dark red inflorescences attracted many insects such as honeybees, wild bees and bumble bees. Therefore, a systematic implementation of amaranth into biogas crop rotations could significantly improve their socio-ecological value in terms of biodiversity conservation and landscape beauty. However, amaranth showed significantly lower dry matter yields (DMY) and specific methane yields (SMY), together resulting in lower methane yields than maize in both years. Therefore, breeding and an optimization of agricultural practices such as sowing density, planting geometry and fertilization management are required to make amaranth more competitive in comparison to maize. To address research question 2, the amaranth field trials mentioned above also included treatments of legume intercropping with runner bean (RB, Phaseolus vulgaris L.) and white clover (WC, Trifolium repens, L.). The RB and WC developed equally well in amaranth and maize each year. For both amaranth and maize, the RB share of total DMY was low (5-10%) and did not significantly affect the total DMY. By contrast, WC had a significant negative effect on the DMY. Overall, the spatial diversification ‘legume intercropping’ could considerably improve the socio-ecological value of amaranth cultivation in terms of biodiversity conservation, greenhouse gas (GHG) mitigation and soil protection. For research question 3, two different wild plant mixtures (WPM) were cultivated on three sites in southwest Germany from the years 2011 to 2015. At each location, the WPM showed great potential for both biodiversity conservation and ecosystem resilience. Numerous insect species were observed in the WPM stands each year, indicating WPM as a relevant cropping system for habitat networking. Furthermore, the aesthetic appearance of the WPM stands over the years demonstrated the potential positive effect WPM cultivation could have on the public perception of biogas production. The DMY of the WPM varied strongly depending on (i) the initial composition of species sown, (ii) the establishment procedure, (iii) the environmental conditions, (iv) the pre-crop, and (v) the number of predominant species. WPM were found to have low demands for fertilization and crop protection. Thus, WPM appear a promising low-input cropping system for the promotion of biodiversity conservation, habitat networking, soil and water protection, GHG mitigation and climate change adaptation. However, high DMY gaps remain a challenge for the practical inclusion of WPM in existing biogas cropping systems. With respect to research question 4, a meta-analysis revealed that available models proved to be much less precise than expected. Although outperforming all available models, the correlation of the new models was still low (up to r = 0.66). It was also found that non-linear terms are of less importance than crop-specific regressors including the intercept. This indicates that across-crop models including crop-specific configurations could help to improve the identification of alternative crops and cropping systems for a more diverse biogas crop cultivation in the future.
Agronomic strategies to reduce potential precursors of acrylamide formation in cereals
(2020) Stockmann, Falko; Graeff-Hönninger, Simone
Food safety is of great importance as harmful substances formed during food processing can negatively affect human health. When the carcinogenic food ingredient acrylamide (AA) accidentally appeared in 2002, it was not expected that AA would take this much attention during the next years. Yet, after around 15 years of research, AA has finally been recognized as being harmful. In a first step, research focussed on food processing implications on AA formation. The impact of heat treatment, time of heating, baking agents, fermentation time, additives and enzymes were reported in several studies. Nevertheless, since 2011 food AA levels seem to stagnate or even increase in some years. Thus, the food industry did not show sufficient progress in reducing AA. Reducing sugars and amino acid free asparagine (Asn) are the main AA precursors. They can fluctuate in their content for instance in grain flour or potatoes shifting the focus of AA origin to the raw material. Thus, the production of raw material low in AA precursors seems important. However, lowering precursors of AA in the raw material necessitates suitable agronomic strategies to grow cereal species and cultivars low, especially in free Asn. Hence, the major goal of this thesis was to investigate the following questions concerning their impact on free Asn formation in cereals: 1. Which role does the management system plays, as organic vs. conventional farming systems highly differ in their cropping strategies? 2. What is the best nitrogen fertilization strategy when comparing organic vs. conventionally cropping systems? 3. Is there an impact of sulphur fertilization concerning sulphur amount and sulphur type? 4. Can expanding row distance and lowering seed density in low-input farming systems positively influence baking quality while keeping free Asn amounts low? 5. For organically grown cereals no level of free Asn was available. Thus, the question came up to which extent organically grown cereal species and cultivars including ancient grains like einkorn and emmer differ in free Asn. 6. Should free Asn be implemented in breeding programs if heritability is high? 7. Is there an impact of harvest timing on free Asn formation? Out of several field trials the following results were obtained: • The cropping system had a significant impact on grain yield, the level of free Asn and quality traits. Across all species, free Asn contents in flour were 26% lower under organic conditions compared to conventional farming. For wheat a maximum reduction of 50% in free Asn content was possible if organically produced. Spelt and rye were affected to a minor extend as only in single years organically grown cultivars showed up to 33% lower Asn contents. • Nitrogen (N) fertilization significantly influenced grain yield and baking quality in both cropping systems. In contrast, up to a certain amount of N free Asn was only affected to a minor extend. In particular, within the organic farming samples no significantly higher free Asn amounts were determined even if N fertilizer was raised or the N form was changed. A late N fertilization within the conventional cropping system increased crude protein content, while no clear effect was found on free Asn. Also, cultivars affected free Asn level significantly. Wheat cultivar Capo exhibited the lowest AA formation potential at a N supply of 180 kg N ha−1 while simultaneously reaching a crude protein content > 15% (conventional) and > 12% (organic). Thus, lowering free Asn by adjusting N treatments should not necessarily affect baking quality. In general, free Asn amounts in wheat varied widely both within cultivars and between cropping systems. Besides N, neither type nor amount of sulphur fertilization influenced free Asn significantly. • Extending row distance can increase quality traits protein and sedimentation value. Seed density was highly related to grain yield and test weight. Most importantly, free Asn was only minor affected by both treatments. Thus, larger row distances can be recommended to raise baking quality in organic farming systems without simultaneously affecting free Asn. Number of grains spike-1 seems to be related to free Asn (R2=0.72). This provides new insights on Asn synthesis during grain development and offers the opportunity to predict free Asn formation without expensive chemical analyzes. In contrast Asn and protein content did not show any relation while high protein contents in grain seem to lower AA amount in heated flour samples. • The impact of organically grown cereal species and cultivars in combination with marginal N supply on free Asn was clearly shown. A reduction potential of 85% was reached if rye was replaced by spelt. Surprisingly, the ancient species einkorn and emmer reached a very high free Asn content similar to rye. Heritability was high for wheat and spelt concerning locations, while regarding years, heritability was low for wheat but high for spelt and rye. For organically grown cereals, the relation between free Asn and AA formation was proven. Across species and years free Asn can serve as an indicator for AA formation (R2 of 0.69). • Harvest timing affects free Asn levels. In this context a delayed harvest can increase Asn significantly while shifting harvest 1-2 weeks earlier decreased Asn by up to 60% depending on cereal species and cropping system. After summarizing and stating the most promising steps in the frame of agronomic strategies to lower free Asn, a prediction tool for free Asn should be implemented that classifies the impact of agronomic strategies and leads to recommendations to farmers. Finally, the main riddle, that should be solved during the next studies is the question, why cereal species and cultivars differ in their Asn formation. This thesis gives some preliminary ideas but a much deeper insight is essential to establish long-term strategies to lower free Asn content.
Alternative phosphorus resources from urban waste as fertilization
(2023) You, Yawen; Müller, Torsten
Phosphorus (P) is an essential macronutrient for plants. Plant roots assimilate P in soil mainly in the form of orthophosphates as H2PO4- and HPO42-. Due to the high reactivity, orthophosphates generally exist at low concentrations in soils that have high P sorption capacity. Besides the indigenous P in soil, fertilizers manufactured from phosphate rock are the main source of P to ensure a satisfactory yield in agricultural production. However, phosphate rock is a limited reserve with uneven quality and is geographically restricted. Technologies for recovering and reusing the P from waste streams were therefore developed to alleviate the dependency on this critical raw material and to promote sustainable solutions. Sewage sludge, which contains most of the P from wastewater, has great potential to produce P-rich products. However, the evaluation of their P availabilities to plants by simple chemical extraction of the product is difficult because they often contain different P species that do not easily dissolve in water. In the first chapter, three types of recycled P fertilizers derived from sewage sludge were tested first in the greenhouse using maize in two different substrates and were incubated in soil for 0, 22, and 56 days. Untreated sewage sludge ash (SSA), Na-treated SSA, and struvite were tested here. Untreated SSA failed to promote the growth of young maize, while Na-treated SSA and struvite achieved similar biomass as mineral P fertilizer. The pre-incubation time had a negative impact on the P use efficiency of recycled fertilizers. Although the P availability of untreated SSA was very low, it might be a potential substitute for phosphate rock to produce fertilizers. In Chapter II, the P availability and heavy metal contamination risk of superphosphate produced with untreated SSA in the lab were investigated. It was found that the superphosphate produced with the mixture of 25% SSA and 75% rock phosphate had a similar P use efficiency as the superphosphate produced with 100% rock phosphate, indicating untreated SSA could be a suitable substitution of rock phosphate in the P fertilizer production. Despite the heavy metal accumulations in soil and plant being minimal, the Pb and Cu concentration in untreated SSA exceeded the maximum limit according to the EU regulation on fertilizers and therefore its use is restricted in fertilizer production. The separation of industrial and municipal sludge before incineration is recommended to obtain SSAs with high P concentrations but less heavy metal. In Chapter III, the P availability of granulated struvite as affected by fertilizer application methods in comparison to di-ammonium phosphate (DAP) was investigated under field conditions. The experiment was conducted in one field in 2020 and repeated in an adjacent field in 2021. Two-year maize results showed an increase of 30% in maize yield and P content when struvite was placed, indicating that fertilizer placement enhanced the efficiency of granulated struvite. Struvite-placed had similar P use efficiency as DAP-placed, and both treatments led to significantly higher yield and P content of maize than no-P control. The residual effect of fertilizer treatment was evaluated with faba bean (Vicia faba) and triticale (Triticosecale Wittm. ex A. Camus.) as subsequent crops after maize. No significant difference in yield and P content was found between struvite-placed and DAP-placed. Nevertheless, this chapter demonstrated that placed struvite can replace DAP as P fertilizer in maize cultivation. In Chapter IV, the sensitivity of three P extraction methods to different P species was investigated to provide insights into the characterization of current soil P tests to plant P availability. Three soil P tests were compared: calcium acetate-lactate (CAL), Olsen, and diffusive gradients in thin films (DGT). Results showed that a portion of added orthophosphates was immediately fixed in the soil and cannot be extracted by any of the methods. The acidic CAL method may overestimate immediately plant-available P of insoluble calcium phosphate like Ca3(PO4)2. The most suitable method to determine immediately available P might be the Olsen and DGT method. To conclude, this dissertation demonstrated the P availability of recycled P fertilizers derived from sewage sludge and possible strategies to enhance their P use efficiencies. It provided agronomic evidence on the feasibility of replacing phosphate rock-derived P fertilizers with recycled fertilizers and insight into its land application. With the recently revised EU regulation on fertilizing products, it can be expected that recycled fertilizers will soon share the market with mineral fertilizers and help develop sustainable agriculture.
Analyse von Wachstum und Qualität von Weizen unter ansteigender CO2 Konzentration als Folge des Klimawandels
(2019) Dier, Markus; Zörb, Christian
The atmospheric CO2 concentration is expected to increase to 500–620 ppm in the future. Such an elevated atmospheric CO2 concentration (e[CO2]) increases grain yield, but can decrease tissue N concentrations by about 9% in wheat. This could endanger global food security. Moreover, in previous studies, a decrease of grain N concentration by e[CO2] has closely been associated with that of gluten proteins, indicating a decreased baking quality under e[CO2]. The mechanisms by which e[CO2] decreases N concentration are still unclear and FACE studies investigating CO2 x N interactions on the formation of grain yield and the quality of winter wheat are scarce. The first main objective was the analysis of a decreased N concentration in the grain by e[CO2] in winter wheat based on a two-year FACE experiment with widely differing N levels (35 to 320 kg N ha-1) and different N forms (NO3- and NH4+). The focus was on key processes of grain N acquisition that are leaf NO3- assimilation, N remobilization and post-anthesis N uptake. The hypotheses were: e[CO2] inhibits leaf NO3- assimilation, e[CO2] decreases N remobilization (Nrem) by decreased N concentrations at anthesis and e[CO2] decreases post-anthesis N uptake (Nabs) by inhibition of leaf NO3- assimilation or acceleration of senescence. The second main objective was the simultaneous analysis of the e[CO2] effect on the grain proteome and baking quality with the hypothesis that e[CO2] reduces gluten proteins and thereby baking quality. e[CO2] increased grain yield in all N levels by 10% to 17% mainly through enhanced grain number per m2 ground area. This was due to increased radiation use efficiency (chapter 2). These increases were smaller under N deficiency compared with high N supply. The reasons were a reduction of photosynthesis capacity by e[CO2] and a sink limitation concerning grain yield due to N deficiency during ear growth. The indication for the reduction of photosynthesis capacity was a decrease of leaf N concentration under e[CO2] regardless of green leaf area index under N deficiency. An indication for sink limitation of grain yield was the decrease of harvest index by e[CO2] because of a strong and small stimulation of stem and ear growth, respectively by e[CO2]. Grain N yield was increased by e[CO2] under all N levels (chapter 3). There was a strong linear relation between grain N yield and grain number that was unaffected by e[CO2]. In contrast with the hypotheses of an decreased Nrem and Nabs under e[CO2], e[CO2] resulted in an increase of Nrem, Nrem efficiency and Nabs, causing the increase of grain N yield. Nevertheless, e[CO2] slightly decreased grain N concentration (by 1 to 6%), whereby the smallest effect of 1% was found under N deficiency. This decrease was primarily related to a growth dilution effect due to an increased individual grain weight under e[CO2]. A further reason was a stronger increase of grain number than an increase of vegetative N yield at anthesis by e[CO2] and thereby a decrease of the ratio between the N source and the N sink. Indication for an e[CO2] induced inhibition of leaf NO3- assimilation was not found as e[CO2] did not result in a decreased activity of leaf nitrate reductase under all N levels at both cool (17 °C) and warm (28 °C) temperatures (chapter 4). Furthermore, the e[CO2] induced stimulation of growth and N acquisition was not stronger under NH4+ compared with NO3- based N-fertilization. Reduction of grain protein concentration by e[CO2] was associated with reduced albumin/globulin and gluten concentrations under all N levels (chapter 5). Under optimal N supply, the grain protein composition was changed by e[CO2] with altogether 19 decreased and 17 increased protein spots. 15 out of the 16 identified decreased proteins were globulins, whereas specific gluten proteins were not found to be affected by e[CO2]. Correspondingly, baking quality remained unaffected under e[CO2] under all N conditions. In conclusion, grain N yields were increased by e[CO2] due to an increase of Nrem and Nabs with grain number being the driving force. Grain N concentrations were slightly reduced under e[CO2] with a growth dilution effect and a changed source to sink ratio as the underlying mechanisms. The reduction of the grain N concentration by e[CO2] was not specifically associated with a reduction of gluten proteins.
Analysis of phytotoxicity and plant growth stimulation by multi-walled carbon nanotubes
(2016) Zaytseva, Olga; Neumann, Günter
Nanotechnology is a rapidly expanding area of science and technology, which has gained a great interest due extraordinary properties of nanomaterials with numerous potential fields for practical application. Meanwhile, carbon nanotubes (CNTs) are among the ten most-produced engineered nanomaterials worldwide with applications in automotive industry, building and construction, electronics, and many other industrial sectors, showing also a great potential for integration into environmental and agricultural applications. However, during the last decade it has been demonstrated that nanomaterials can exert significant and extremely variable effects also on living organisms. In higher plants, both, positive and negative responses on growth and development have been reported but the related mechanisms are still not entirely understood. This study presents a systematic assessment of CNT effects on representative crops under standardized conditions with special emphasis on interactions with plant nutrition. After the introductory background (Chapter 1), presenting a comprehensive literature review on carbon nanomaterials with special emphasis on plant responses, environmental and agricultural applications, Chapter 2 describes the impact of selected multi-walled carbon nanotubes (MWCNTs) on seed germination and early seedling development of different crops (soybean−Glycine max, maize−Zea mays, and common bean−Phaseolus vulgaris). In face of highly variable plant responses to CNT treatments reported in the literature, the study was designed as a systematic analysis under standardized growth conditions, dissecting the effects of one single type of MWCNTs, depending on plant species, MWCNT dosage, duration of exposure to MWCNT treatments, and plant-developmental stage, including imbibition, germination and seedling development. Short-term seed treatments (36 h) with MWCNTs reduced the speed of water uptake particularly by soybean seeds, associated with an increased germination percentage and reduced formation of abnormal seedlings. However, during later seedling development, negative effects on fine root production were recorded for all investigated plant species. Inhibition of root growth was associated with reduced metabolic activity of the root tissue and a reduction of nitrate uptake, which could be mainly attributed to the smaller root system. The results demonstrated that even under standardized growth conditions largely excluding external factors, plant responses to MWCNT exposure exhibit differences, depending on plant species but also on the physiological status and the developmental stage of individual plants. Soybean was selected as a model plant for further studies since both, positive and negative effects of the same dose of MWCNTs (1000 mg L-1) could be observed even in the same individual plants. Chapter 3 investigates effects of short-term soybean seed exposure (36 h) to MWCNTs on seedling development, depending on the nutrient availability of the substrate. At 8 DAS stunted growth and poor fine root production were first detectable in seedlings germinating on moist filter paper without additional nutrient supply. This effect was preceded by reduced metabolic activity of the seedling tissues detectable by vital staining already at 2 DAS. Root growth inhibition was a long-lasting effect, detectable in soil culture up to 38 DAS. More detailed investigations revealed zinc (Zn) deficiency as a major growth-limiting factor. The growth of affected soil-grown plants was recovered by foliar application of ZnSO4 or by cultivation in nutrient solution supplied with soluble ZnSO4. A more detailed investigation of the physiological mechanisms related with the inhibitory effects of MWCNTs on plant growth is presented in Chapter 4. Oxidative stress was identified as a major factor determining MWCNT-induced root growth inhibition in soybean, demonstrated by recovery of root development after external supplementation with antioxidants. Induction of oxidative stress by MWCNT application was detectable already after the 36 h imbibition period particularly in the tips of the radicle as indicated by accumulation of superoxide anions, reduced triphenyltetrazolium chloride vital staining, and induction of superoxide dismutase activity. The expression pattern of the oxidative stress indicators coincided with preferential accumulation of MWCNTs in the cells of the root tip and was reverted by external application of proline as antioxidant. MWCNT-induced plant damage could be reverted by external supplementation of micronutrients (Zn, Cu, Mn) as important cofactors for various enzymes involved in oxidative stress defense (SOD, biosynthesis of antioxidative phenolics). Accordingly, SOD activity increased in seedling roots after Zn supplementation. During germination, the CNT treatments inhibited particularly the Zn translocation from the cotyledons to the growing seedling, and CNTs exhibited a selective adsorption potential for Zn and Cu, which may be involved in internal immobilization of micronutrients. Therefore, this study demonstrated for the first time that phytotoxicity of CNTs is linked with disturbances of micronutrient homeostasis during seedling development. Implications for environmental phytotoxicity assessment of MWCNTs and their potential applications in agriculture are discussed in a final overview presented in Chapter 5.
Analysis of the interaction between the helper component proteinase (HC-Pro) of Zucchini yellow mosaic virus (ZYMV) and the plant RNA methyltransferase Hua enhancer 1 (HEN1)
(2012) Jamoos, Rana; Reustle, Götz
The helper component-proteinase (HC-Pro) is a multifunctional protein found among potyviruses. It plays multiple roles in the viral infection cycle and some of these functions have been mapped to different regions of the protein. The subcellular localization of several viral RNA silencing suppressor (RSS) proteins was identified. In this study, we have shown that the Zucchini yellow mosaic virus (ZYMV) HC-Pro wild type (HC-ProFRNK) and its mutant, HC-ProFINK, had a diffuse cytoplasmic localization and formed aggregates along the endoplasmatic reticulum (ER). HC-ProFRNK and HC-ProFINK were stably expressed in N. benthamiana and A. thaliana plants. In addition, the HC-ProFRNK and HC-ProFINK were fused to a nuclear localization signal (NLS) sequence (NLS-HC-ProFRNK and NLS-HC-ProFINK) and these transgenes constructs were also stably transformed into N. benthamiana and A. thaliana. Expression of all four transgenes caused different effects in the two plant species. HC-ProFRNK?producing A. thaliana plants displayed severe phenotypic alterations. In A. thaliana, the HC-ProFINK led to a reduced number of seed set. In N. benthamiana expressing HC-ProFRNK/FINK, generally no or only slight phenotypic changes were monitored. The NLS-HC-ProFRNK/FINK-producing plants displayed clear phenotypes. Flower malformations and severe reduction of seed set were the most conspicuous observations made. In general, more severe developmental disturbances were observed in transgenic A. thaliana than in N. benthamiana plants. ZYMV HC-Pro RSS activity was previously demonstrated in N. benthamiana plants by transient expression experiments. In this study, RSS activity was confirmed in N. benthamiana lines stably expressing ZYMV HC-ProFRNK/FINK. Notably, these plants did not show significant morphological alterations. Because the RSS activity of HC-Pro leads to enhanced transgene expression, our ?symptom-free? transgenic N. benthamiana plants may serve as a platform for over-expression of foreign genes. In tobacco, transient or over-expression of rgs-CaM mimicked the phenotypic effects of Tobacco etch virus (TEV) HC-Pro, indicating that TEV HC-Pro may up-regulate rgs-CaM expression. However, our data revealed no significant difference in the levels of rgs?CaM mRNA in N. benthamiana plants expressing HC-ProFRNK/FINK when compared with the steady-state mRNA level found in the wild type plants. It is likely that RSS proteins from related viruses do not necessarily exhibit identical effects on RNA silencing. In addition, plant species might also differentially respond to identical RSS proteins. The small RNA (sRNA) binding activity of HC-Pro was evident in N. benthamiana plants co-expressing the HC-ProFRNK and an infectious transgene construct of Potato spindle tuber viroid (PSTVd). In comparison to PSTVd-infected N. benthamiana plants, Northern blot analysis showed increase accumulation of viroid-derived sRNAs in the double transformed plants. There is indirect evidence showing that in plants, transient or stable expression of HC-Pro results in decreased accumulation of methylated sRNAs. In this study, we demonstrated that recombinant ZYMV HC-Pro inhibited the methyltransferase activity of the A. thaliana Hua enhancer 1 (AtHEN1) in vitro. Moreover, we found that HC-ProFINK lacking sRNA-binding activity, also inhibited AtHEN1 activity. In contrast, truncated HC-Pro and total soluble bacterial proteins did not affect AtHEN1 activity. Using enzyme-linked immunosorbent assays, we provided evidence that the HC-ProFRNK/FINK, both bound to AtHEN1. Our results strongly indicated that inhibition of the AtHEN1 activity by HC-Pro is probably due to direct interactions between both proteins. We concluded that AtHEN1 inhibition and sRNA-binding activities of HC-Pro are independent of each other. Using the yeast two-hybrid (Y2H) system, we could show that in contrast to RSS proteins from some other viruses, the HC-ProFRNK/FINK proteins did not interact with the Argonaute 1 (AGO1) protein. Similar to previous reports our data confirmed that HC-Pro interacts with itself to form homodimers. Notably, only HC-ProFRNK but not HC-ProFINK was able to interact with itself. The conserved FRNK box is located in the central domain of HC-Pro and this domain has been previously shown to be involved in self-interaction. It should be noted that parts of the work have been published in: - Jamous R. M., Boonrod K., Fuellgrabe M. W., Ali-Shtayeh M. S., Krczal G. and Wassenegger M. (2011). The HC-Pro of the Zucchini Yellow Mosaic Virus (ZYMV) inhibits HEN1 methytransferase activity in vitro. J. Gen. Virol. 92, 2222-2226. - Fuellgrabe M., Boonrod K., Jamous R., Moser M., Shiboleth Y., Krczal G. and Wassenegger M. (2011). Expression, purification and functional characterization of recombinant Zucchini yellow mosaic virus HC-Pro. Protein Expr. Purif. 75: 40-45.
Approaches to improve the implementation and expansion of Miscanthus production
(2016) Xue, Shuai; Lewandowski, Iris
Several species within the miscanthus genus (Miscanthus spp.) are characterized by high biomass yields and low production input requirements. This raised increasing interests in their applications for bioenergy. However, to date, only small areas of Miscanthus × giganteus (approximately 40,000 ha) are commercially grown and used for generating electricity and heat in Europe, where miscanthus has been developed as bioenergy crop for more than decade. Reviewing state-of-the-art revealed four main factors limiting the implementation of miscanthus production. These are inefficient and expensive propagation techniques, land use dilemma (i.e. lack of land available for growing miscanthus), lack of varieties/genotypes adapted to various and especially to stressful environmental conditions and lack of efficient agronomic practices for miscanthus establishment. Against these limiting factors, this thesis aims to (1) evaluate the different propagation systems with regard to technologies and costs, and improve the preferred rhizome propagation techniques; (2) address the land use dilemma through exploring marginal land (i.e. non-arable land with ability to grow plants with tolerance to environmental stresses) for miscathus production; (3) and screen optimal genotypes and effective practices for establishing and managing miscanthus on marginal land in a case study on grassland. To achieve the first objective, a review, our own field trials and farmer surveys were performed. Direct seed sowing was found to be the cheapest propagation method (1,508.5 € ha-1 overall establishment costs) and micro-propagation the most expensive (6,320.8 € ha-1). Direct rhizome planting is the farmers’ most preferred and most applied establishment method and has moderate establishment cost of 1,904-3,375.7 € ha-1. However, it goes along with the lowest propagation efficiency (1:10) and consequently restricts the availability of propagation material for large-scale plantations. However, the multiplication ratio can be increased by reducing the rhizome size. Field trial results showed that 6-cm length is close to the minimum size of rhizome that can germinate after directly planting into field. Compared to the traditionally used macro-rhizome, the multiplication ratio of the improved rhizome propagation (using 6-cm rhizomes) is tripled. In addition, the multiplication ratio can also be increased by transplanting rhizome- or stem-derived plantlets. However, due to higher labour and energy inputs required for the pre-growing of plantlets, their establishment cost reduction potential is limited, with estimated costs of 4,240.8-4,400.8 € ha-1. Direct seed sowing as the cheapest method is presently only possible for Miscanthus sinensis and not yet practical under German conditions. In addition, the seed-setting rate of M. sinensis is very low (0.0-28.7%) under the climatic conditions of south-west Germany, making commercial seeds production difficult. For all the propagation methods considered, more research efforts are still required to reduce the material production costs and simultaneously increase the multiplication ratio. For the second objective, the production potential of miscanthus on marginal land in China was assessed. Because China has limited agricultural land resources and its non-food bioenergy policy (it is only allowed to grow energy crops on marginal land) is adamant, there is a desideration for exploiting its marginal land potential. In this study, Geographic Information System (GIS) techniques, model simulation were adopted to identify the productive marginal areas for miscanthus and to estimate their biomass and bioenergy production potentials. The results show that in China there are large marginal land areas of 17,163.54 × 104 ha available for growing miscanthus. However, due to limitation by low winter temperatures and low precipitation levels in some areas, the total marginal area suitable for growing miscanthus is only 769.37 × 104 ha. The Monteith radiation yield model was used to determine the potential miscanthus yield in Chinese climatic conditions. The simulation gave the actual harvestable yield levels on arable land of 18.1-44.2 odt ha-1 yr-1. Taking the environmental stresses of marginal conditions into account an achievable miscanthus yield potential on marginal land of 2.1-32.4 odt ha-1 yr-1 was calculated (varying between different marginal land types). Based on these achievable yield levels, the total miscanthus production potential on the entire suitable marginal land areas is 13,521.7 × 104 odt yr-1; the corresponding bio-electricity generation and total greenhouse gas saving potentials are 183.9 TW h yr-1 and 21,242.4 × 104 t CO2 eq. yr-1, respectively. The spatial distribution of the suitable marginal areas shows that they are mainly concentrated in the central part of Northeast China and the Loess Plateau. Both regions are recommended as priority development zones for the Chinese miscanthus-based bioenergy industry. However, implementation of this huge marginal land potential is currently constrained by many barriers, e.g. concerns on potential ecological effects, competition for marginal land from other uses, lack of high yield varieties in marginal conditions. Lack of varieties with suitability to marginal conditions and efficient agronomic practices for the establishment on marginal land are the main barriers that limit using marginal land for miscanthus production. Therefore, stress tolerant varieties need to be selected and methods of effective establishment of miscanthus on marginal land need to be developed. Worldwide, grassland is the most important marginal land type because it has the largest terrestrial area and mild environmental stresses for growing energy crops (including miscanthus). However, it is undesirable or even legally prohibited to convert grassland into bioenergy cropland to avoid biodiversity loss and soil carbon being reduced by tilling practices. Hence, no-till establishment practices for miscanthus establishment and maintenance on grassland are investigated here under the third objectives. Our study demonstrates that miscanthus can be successfully cultivated on both good (nutrient-rich) and marginal (nutrient-poor) grassland using the proposed agronomic practices and an increased grassland productivity may be achieved through the establishment of suitable miscanthus genotypes. The recommended agronomic practices are summarized as following. Miscanthus genotypes with tall, thick shoots perform better than those with short, thin shoots. Better establishment is achieved when rhizome-derived plantlets are transplanted into pre-disturbed grassland. The grassland pre-disturbance of low vegetation cutting (5 cm) and herbicide spraying in narrow stripes is recommended for its beneficial effect on miscanthus establishment without significant negative effects on grassland productivity. Two harvests, one in late spring and one in late autumn, are optimal to achieve a high grassland yield. In this thesis, the limitation of the inefficient propagation technique was mitigated through minimizing the rhizome size and exploring the seeds propagation potential. The land-use dilemma was alleviated by exploring the marginal land production potential. Additionally, constrains of lack of genotypes and agronomic practices for the miscanthus establishment on marginal land were improved by field trials on grassland (the most important marginal land type with a huge potential).These results can improve the implementation and expansion of miscanthus production. However, in addition to constrains improved in this thesis, the miscanthus production is currently constrained by many other technical, economic and financial, social and political, environmental issues. It is unlikely that the implementation and expansion will achieve without mitigating these constrains. Further research and support should address these barriers in an integrate manner.
Aspects of stomatal physiology during salt-stress-related disturbances of ion homeostasis
(2020) Franzisky, Bastian Leander; Zörb, Christian
Soil salinity is a major challenge for agriculture, because most crop plants are sensitive to high salt concentrations in soil, an environment that results in reduced growth and yield. One major constraint imposed by salinity is the disruption of ion homeostasis attributable to the uptake competition of salts and nutrients and the accumulation of deleterious ions, which are toxic to plants at high concentrations. For a better understanding of ion-homeostasis-associated traits contributing to salt tolerance in salt-sensitive crops, such as Vicia faba and Zea mays, the capabilities of ion exclusion and tissue tolerance were assessed in diverse genotype selections under saline conditions. In addition, the impact of increased salt ion concentrations in leaves and in the apoplast on stomatal physiology and guard cell integrity was characterized in V. faba exposed to long term salinity in order to improve our knowledge of stomatal physiology and functioning under conditions of NaCl stress. The treatment of diverse V. faba varieties with 100 mM NaCl demonstrated that ion homeostasis-associated tolerance mechanisms are differentially managed for Na+ and Cl-. The longer-withstanding varieties were tolerant to the accumulation of Na+ suggesting that tolerance to Na+ predominantly occurred at the level of tissue tolerance after Na+ had entered the leaves. Conversely, tissue tolerance for Cl- was weak throughout all varieties suggesting that the tolerance to Cl- was facilitated instead by the restriction of the intrusion of Cl- into the plant’s shoots; this process might be crucial for the ability of V. faba to withstand NaCl salinity. The treatment of diverse Z. mays hybrids with mild and high doses of Cl- added to the soil revealed that most genotypes restricted Cl- root to shoot translocation. This suggests that Z. mays effectively prevents Cl- from entering the xylem and, thus, the acropetal transport of Cl-, thereby hindering harmful Cl- accumulations building up in the photosynthetically active leaf blades. A detailed analysis of guard cell physiology under long-term NaCl demonstrated that guard cell primary metabolism differentially responds to altered ion composition resulting from salt stress in comparison with whole leaf tissue in V. faba; such a differential response might be a prerequisite for the maintenance of guard cell functionality under conditions of stress, i.e. the adjustment of guard cell turgor that affects stomatal aperture and water loss. Moreover, the shift from a photoperiod dependent accumulation of sucrose in guard cells and the apoplast to a photoperiod independent under salinity suggests that a metabolic sucrose-mediated feedforward mechanism is involved in coordinating stomatal closure under conditions of long term NaCl and might be beneficial for reducing water loss under conditions of stress related carbon partitioning. In summary, this work shows that ion-homeostasis associated tolerance traits vary between crop species and that the differential metabolic acclimatisation of guard cells to disturbed ion homeostasis might represent an important aspect of tissue tolerance enabling the maintenance of stomatal regulation during long term salinity.
Assessing social aspects of biobased value chains
(2024) Marting Vidaurre, Nirvana Angela; Lewandowski, Iris
Achieving human well-being for all humanity, reducing inequality, and eradicating poverty while preserving the environment are the aims of sustainable development. The bioeconomy offers alternative ways of utilising biomass and other biogenic resources with the objective of addressing global challenges relevant for sustainable development such as resource scarcity, climate change and food security. Lignocellulosic perennial crops like miscanthus, have been investigated as a sustainable source for energy and materials. While various studies assessing the environmental performance of lignocellulosic crops have been published, the analysis of the social dimension of such systems has been little explored. Existing frameworks to perform social assessments are general in their coverage of social aspects and provide long lists of social impact categories, for which adaptation and prioritization is needed according to the specific case being analysed. Furthermore, existing methodologies for social life cycle assessment (S-LCA) leave the practitioner to choose between pursuing a context-specific analysis or a general (country or sector specific) analysis considering the value chain. To date there is no methodology to perform a S-LCA in an integrated manner for both the foreground and background systems of a biobased value chain, which takes into account the different requirements for analysing these systems. The foreground system is composed by the core processes being analysed, while the background system is constituted by the processes needed to supply inputs required for the foreground system. This doctoral thesis aims to develop an integrated methodology to assess the foreground and the background systems of biobased value chains, which combines techniques for performing a context-specific assessment of the foreground system and a generic assessment of the background system. The overall question that this study aims to answer is how to proceed in assessing the social aspects of a biobased value chain covering both the foreground and the background systems of a production process considering the study is an ex-ante analysis? The specific objectives to answer this question are i) to identify which social aspects are relevant for the assessment of biobased value chains, ii) to identify which aspects are to be considered when assessing the potential social impacts of agricultural production processes on the stakeholder “farmer” and iii) to develop a social risk assessment approach that is regionalized in order to assess the potential social impacts within biobased value chains. To achieve the first objective a literature review of empirical studies covering social impacts of agricultural and forestry value chains was performed. This helped in the identification of social aspects that are often assessed and reported. Then the Methodological Sheets for Subcategories in S-LCA were used as a reference to allocate the social aspects reported and evaluated by empirical literature and review studies to those impact subcategories proposed by the sheets. This enabled the identification of social aspects often assessed and those potentially overlooked in the sheets. To achieve the second objective a survey among farmers in a region of Croatia was conducted. Additionally, the study aimed to assess the feasibility of cultivating miscanthus in the region, taking into account potential challenges and opportunities, as well as farmers' willingness to adopt the crop miscanthus. The third objective of performing a regionalized social risk assessment of a biobased value chain was achieved by following the SOCA approach in combination with EXIOBASE 3 as a source of regional information on the origin of inputs and for the estimation of worker hours. This analysis used a case study based on the production of advanced biofuels in Croatia to assess the shortcomings of the methodology. The results showed that the Methodological Sheets for Subcategories in S-LCA provide good coverage of social topics relevant for biobased value chains, but that the stakeholders “smallholder” and “family farm” are not adequately addressed. Drawing on the empirical literature reviewed, the study emphasizes the relevance of these stakeholders in the analysis of biobased value chains, and proposes criteria for consideration in the assessment of these stakeholders. Furthermore, the interviews with farmers revealed that the aspects most valued by them were health and safety, access to water, land consolidation and rights, income and local employment, and food security. Responses to the question of whether they would adopt the crop miscanthus highlight the importance of an established market, good trading conditions and profitability of cultivation. The farmers regarded the provision of subsidies as one of the main factors that make a crop attractive. Opportunities for the adoption of the miscanthus cultivation are related to high yields and low input requirements. Barriers include land conflicts and land availability. Results also showed that mainly harvesting operations were identified as hotspots in the local agricultural operations due to the amount of worker hours required for these processes in comparison to the rest of the agricultural operations. The main contribution of this study is the development of an integrated approach that provides guidance for assessing comprehensively the foreground and background systems of biobased value chains. This consists of a local perspective and a value chain perspective of not yet established value chains. The methodology and framework developed serve for the early identification of potential social impacts in biobased value chains, specifically agricultural value chains. In the current literature, this methodology could be part of what is called materiality assessment. The theoretical framework developed serves for the analysis of the stakeholders “smallholder” and “family farm” and recommends the subsequent involvement of this stakeholder in the selection of context-relevant impact categories. The participation of these stakeholders is important to acquire local knowledge and to select impact categories that reflect their interests, merging a top-down with a bottom-up approach. The social risk assessment to analyse the background system should be applied when the value chain suppliers are not known and when a rapid assessment of the social risk of the value chain is required. The ultimate goal of S-LCA is to provide quality information about potential social impacts in production systems to decision makers, which will take action to reduce inequalities in the different regions of the world and thus contributing to achieve a more sustainable economy.
Banana weevil borer (Cosmopolites sordidus)
plant defense responses and control options
(2021) Bakaze, Elyeza; Wünsche, Jens Norbert
Each year 25-75% of banana yields are lost to Cosmopolites sordidus, one of the major pests of banana/plantain plants. This loss is common with resource-limited farmers who cannot afford the frequent application of insecticides due to their cost and developed resistance by weevils. Larvae, the most destructive life stage, occupy ecologically different microenvironments from adult weevils, thus least affected by synthetic insecticides. Feeding of larvae on banana rhizomes interferes with the established and emerging roots which reduce water and nutrient uptake and consequently weaken the plant stability during windy weather. Integrated pest management (IPM) is being promoted, for a single control strategy produces limited and or unsustainable results. IPM options for banana weevils include habitat management (cultural control), biological control, host resistance, botanical control and chemical control as last resort. Of the above IPM strategies, this research evaluated host resistance, botanical plant extracts and entomogenous fungi to contribute to the overall goal of reducing synthetic insecticides use. In the evaluation of host resistance, physiochemical of phenolic origin; lignin, and suberin were considered. Comparably, weevil and methyl jasmonate treatment, induced higher deposits of lignin and suberin, cellular modifications, and high total phenolic content as well as antioxidant capacity in “Km5” than “Mbwazirume” banana cultivars. Induced polyphenols reduced weevil damage to less than 5% in “Km5” compared to 11% damage in the “Mbwazirume” cultivar. However, with the onetime application of 0.01% methyl jasmonate, “Mbwazirume”, had 50% reduced weevil damage compared to untreated control. Extracts from dried clove buds (Syzygium aromaticum), pepper fruits (Piper guineense) and neem seeds (Azadirachta indica) and their synthetic analogs were evaluated as botanical control option to Carbofuran against C. sordidus in the laboratory and infested field experiments. Efficacy of plant extracts and their synthetic analogs, revealed egg hatch inhibitory effect, larvicidal toxicity and adult repellency variation. For instance, clove extracts and its synthetic analogs had the lower egg inhibitory dose (ID50) of 0.08 to 0.22% than black pepper (0.24 to 0.75%), and half the ID50 value caused 50% larvae mortality. However, in 6 to 48 hours pepper repelled 80 - 98%, clove 78 - 90% and neem 63 - 75% adult weevils, an effect that significantly (P =0.001) reduced field weevil population. Lastly, three Entomogenous fungi; Curvularia senegalensis, Fusarium verticillioides, and Fusarium oxysporum species complex (FOSC) were also evaluated for their ability to infect weevil eggs, larvae and adult weevils, and to reduce weevil damage in potted plants. C. senegalensis and F. verticillioides greatly affected egg hatching and larval survival, for instance, they caused 75 to 90% eggs hatch inhibition, unlike the 25 to 55% egg hatch inhibition for Beauveria bassiana and FOSC. Besides that, fungal treated plants 14 days before weevils, had significantly high SPAD value (P <0.0001), less than 20% rhizome damage and predictive weevil mortality R2 = 0.46. Rhizome damage was greatly reduced by C. senegalensis, followed by B. bassiana and F. verticillioides, and it is the first record to demonstrate that C. senegalensis and F. verticillioides are pathogenic to C. sordidus. In conclusion, an IPM that combines host resistance with locally available botanic extracts and effective entomogenous fungi may provide a sustainable intervention in the management of the weevil population and their damages to benefit both commercial and resource-limited farmers.
Bedarfsgerechte Stickstoffernährung von Hopfen (Humulus lupulus L.) durch Düngesysteme mit Fertigation
(2021) Stampfl, Johannes; Ebertseder, Thomas
In terms of quantity, nitrogen is the most important and most yield limiting plant nutrient in hops (Humulus lupulus L.), whereby excess nitrogen not taken up by the hop plant is subject to various loss processes. Despite that, little is known about the exact effects of an N supply varying in rate and timing for the hop varieties and cultivation systems currently used in the Hallertau, the worlds most important hop-growing region. In the Hallertau, the required amount of nitrogen is largely supplied by surface spreading of granulated N fertilizers, whereas in semi-arid growing regions, high proportions are applied via irrigation water (fertigation). The aim of this thesis was to examine nitrogen fertilization systems with fertigation under the conditions in the Hallertau region with regard to a nitrogen nutrition that is based on the hop plant’s needs. Therefore, four research questions with different sub-aspects have been formulated, as explained below. From 2017 to 2019 the experimental research and the acquisition of empirical data has been conducted in various field trials consisting of three trial series examining the most important hop varieties at different locations. Apart from a variation in rate and timing of N fertilization, different fertilizer application forms (surface application of granulated fertilizer and above- or below-ground fertigation) have also been examined. In addition to the determination of yield, quality and N-uptake at the time of harvest, further analysis methods such as the 15N-Tracer-Technique, chlorophyll value measurements (SPAD-Meter) or passive reflection measurements were used in individual field trials to depict the N-uptake and N-distribution in different parts of the plant. a) Which effects have different nitrogen treatments varied in rate and timing? These studies found that the hop plant absorbs more than two thirds of the total amount of nitrogen over a period of 7 to 8 weeks between early June and end of July - during formation of main biomass. Despite the fact that only a low amount of nitrogen is accumulated in the plant prior to this stage, the varieties Perle and Tradition showed that a nitrogen deficit in early growth stages until end of May already leads to a decrease of yield potential. This is due to a change in the variety-characteristic formation of lateral shoots (side arms) - the later the application of nitrogen, the greater the formation of side arms was reduced, starting from the bottom to higher plant sections. Consequently, a nitrogen fertilization solely based on the hop plant’s N uptake curve cannot be recommended, neither regarding yield formation nor nitrogen utilization. Instead, an early application of the first nitrogen treatment in April is of vital importance for early maturing varieties such as Perle and Tradition. Late maturing varieties like Herkules show a higher potential of compensation due to prolonged growth phases which enables a higher adaption of N-Fertilization to the plant’s N uptake curve. The ideal amount of nitrogen fertilization with regard to yield optimization has been determined by the growth pattern - depending on variety, weather conditions and location - and therefore by the N uptake, the supply of mineral nitrogen in the soil as well as the location-specific N mineralization potential. A reduction of the nitrogen fertilization to a level significantly below the plant’s N uptake not necessarily led to a limitation of biomass and yield formation in the same year, however, it resulted in an accelerated ripening and a negative impact on external cone quality. Furthermore, it showed that the storage of nitrogen in specific storage roots declines if N levels are significantly reduced, leading to lower vitality as well as limited plant development and yield formation in the following year. With regard to the hop plant’s perennial properties as well as the goal to achieve a demand-oriented nitrogen nutrition of the hop plant it is also necessary to supply the storage roots with enough nitrogen. With respect to valuable contents of alpha acid it has been found that high N supply levels during the stage of alpha acid synthesis (starting from early August) can result in a reduction of alpha acid concentration in the variety Herkules. This decrease can be caused by late and excessive N fertilization as well as by high mineral N contents in the soil. However, this effect has not been observed in the aroma varieties Perle and Tradition. b) Is it possible to determine the current nitrogen nutritional status through non-invasive methods? The measurement of the chlorophyll value with a SPAD-Meter on the lower leaves of the main shoot generally reflected the N content and N supply status of the hop plant. However, short-term changes in the N nutritional status could not be recorded with sufficient accuracy at this measuring point, especially not during the stage of main biomass formation, since increased proportions of the applied nitrogen were transported to higher plant sections, as was shown by the use of 15N. Regarding the determination of threshold values a classification of the plant development into before, during and after main biomass formation independent of the measuring point, is considered appropriate, since the chlorophyll value correlates with the plant’s development stage. Vegetation indices, calculated on the basis of reflectance spectra, represent not only the N content but also the actual N uptake of the crop, which is why passive reflectance measurement methods have a higher informative value with regard to the current N supply status of the plant compared to chlorophyll value measurements. Therefore, this technology could be used to achieve a site-specific optimization of rate and timing of N fertilization and thus a more demand-oriented nitrogen nutrition of the hop plant in the future. c) What are the effects of surface and subsurface drip irrigation? In the period from 2017 to 2019, additional irrigation of the aroma variety Perle on sandy soil led to a stabilization of the agronomic parameters cone yield and alpha acid content every year. In addition, irrigation also achieved an improvement of nitrogen utilization. Compared to subsurface systems, surface drip irrigation achieved a higher efficiency if the horizontal water distribution was limited by hydraulic soil properties. It was shown that this is due to the fact that the majority of the hop plant’s fine root system is located in the hill formed along the hop rows and the soil layers beneath it. d) What are the effects of a nitrogen nutrition via irrigation water? A system comparison was made between N fertilization systems with fertigation and a solely granulated N application. The use of fertigation resulted not only in an improvement of cone yield and alpha acid content, but also in an increase of the plants nitrogen uptake and a reduction of Nmin content in the soil, which is also associated with a reduction of the risk of nitrate leaching into the groundwater. Fertilization systems with fertigation achieved a higher nitrogen utilization especially at low N-fertilization rates. If two thirds of the total amount of nitrogen were applied via irrigation water, the concentration over a 6-week period proved to have a positive impact on all analyzed varieties, especially under conditions of a limited N supply, since a higher proportion of N has been applied during main biomass formation and the stage of lateral shoot growth. For an efficient N-fertilization with fertigation the application should take place between mid-June and late July while no significant amounts of nitrogen should be applied after early August. For early maturing varieties such as Perle and Tradition, there is a risk of a late N application as it is hardly possible to lay out the drip tubes before the 25th week of the year. Therefore, in early maturing varieties, a higher proportion of N should be applied in earlier growth stages while the amount of N applied via fertigation should be less than two-thirds of the total amount of N fertilizer. A substantial advantage of fertilization systems with fertigation is that nitrogen applied via the irrigation water is immediately absorbed by the plants, which allows an effective short-term intervention in the plant’s nitrogen nutrition. On the basis of a reliable recording of the current N supply status with sensors during the main growth stage, fertigation could be used to adjust the N fertilization in order to achieve a site-specific and demand-oriented nitrogen nutrition of the hop plant.
Bio-effector based fertilization strategies to improve drought stress tolerance and phosphate efficiency in potato
(2024) Mamun, Abdullah Al; Neumann, Günter
Due to shallow root systems, potato is considered as a drought sensitive crop. To counteract these limitations, application of plant growth-promoting microorganisms (PGPMs) is discussed as a strategy to improve nutrient acquisition and biotic and abiotic stress resilience. However, particularly initial root colonization by PGPMs can be affected by stress factors with negative impact on root growth and activity or the survival of PGPMs in the rhizosphere. Initial screening experiments (Chapter 3) investigated drought-protective effects of six fungal and bacterial inoculants and ten combinations thereof (microbial consortia) on vegetative growth, nutritional status and tuberization of potato under controlled conditions. It was hypothesized that microbial consortia would offer improved drought protection as compared with single strains due to complementary or synergistic effects, with a differential impact also of the N fertilization management. Under nitrate fertilization, a 70% reduction in water supply over six weeks reduced shoot and tuber biomass by 30% and 50%, respectively and induced phosphate (P) limitation. The P-nutritional status was significantly increased above the deficiency threshold by three single strain inoculants and eight consortia. This was associated with the presence of the arbuscular mycorrhizal (AM) inoculant Rhizophagus irregularis MUCL41833 (5 cases) and stimulation of root growth (5 cases). Additionally, Bacillus amyloliquefaciens FZB42 and an AM + Pseudomonas brassicacearum 3Re2-7 combination significantly reduced irreversible drought-induced leaf damage after recovery to well-watered conditions. However, despite beneficial effects on vegetative growth, the microbial inoculants did not mitigate drought-induced limitations in tuber formation, neither in greenhouse culture nor in field experiments. Contrary to nitrate supply, ammonium dominated fertilization significantly increased tuber biomass under drought stress, which was further increased by additional AM inoculation. This was associated with (i) improved enzymatic detoxification of drought-induced reactive oxygen species (ROS), (ii) improved osmotic adjustment in the shoot tissue (glycine betaine accumulation), (iii) increased shoot concentrations of ABA, jasmonic acid and indole acetic acid (IAA), known to be involved in drought stress signaling and tuberization, and finally (iv) reduced irreversible drought-induced leaf damage. Additional application of the bacterial inoculants FZB42, 3Re2-7 or Herbaspirillum further improved ROS detoxification by increased production of antioxidants. However, this resulted in stimulation of biomass allocation towards shoot growth at the expense of tuber development. The results demonstrated that compared with single strain inoculants, microbial consortia used as inoculants can increase the probability for complementary plant-protective effects under environmental stress conditions. However, the absolute effect size is not always different. Drought-protective effects on vegetative growth do not necessarily translate into yield benefits and are affected by the form of N supply and the selected inoculant strains. Application of silicatic soil conditioners to improve soil water relationships under drought stress may be strategy to support rhizosphere establishment of PGPM inoculants with drought-protective potential under conditions of water deficit. In Chapter 4, perspectives for the use of commercial silicatic soil conditioners (SC) supposed to improve soil water retention, were investigated. The SC products were based on combinations of silicatic rock powder with lignocellulose polysaccharides (Sanoplant® = SP) or polyacrylate (Geohumus® = GH). It was hypothesized that SC applications would support beneficial plant-inoculant interactions with Rhizophagus irregularis MUCL41833 & Pseudomonas brassicacearum 3Re2-7 on a silty loam soil-sand mixture under water deficit conditions. Although no significant SC effects on WHC and total plant biomass were detectable, the SC-inoculant combinations increased the proportion of leaf biomass not affected by drought stress symptoms (chlorosis, necrosis) by 66% (SP) and 91% (GH). Accordingly, osmotic adjustment (proline, glycine betaine accumulation) and ROS detoxification (ascorbate peroxidase, total antioxidants) were increased. This was associated with elevated levels of phytohormones involved in stress adaptations (abscisic-, jasmonic-, salicylic-acids, IAA) and reduced ROS (H2O2) accumulation in the leaf tissue. In contrast to GH, the SP treatments additionally stimulated AM root colonization. Finally, the SP-inoculant combination significantly increased tuber biomass (82%) under well-watered conditions and a similar trend was observed under drought stress, reaching 81% of the well-watered control. The P status was sufficient for all treatments and no treatment differences were observed for stress-protective nutrients, such as Zn, Mn, or Si. By contrast, GH treatments had negative effects on tuber biomass, associated with excess accumulation of Mn and Fe in the leaf tissue close to the toxicity levels. The findings suggest that inoculation with the PGPMs in combination with SC products (SP) can promote physiological stress adaptations and AM colonization to improve tuber yield of potato, independent of effects on soil water retention. However, this does not apply for SC products in general. Chapter 5 investigated an optimized PGPM application technology based on granulated organic fertilizer formulations (Minigran®), specifically adapted to improve the shelf life of selected microbial consortia. Microbial consortia were based on selected strains of Pseudomonas brassicacearum (Cons1), Paraburkholderia phytofirmans (Cons2) and Paraburkholderia phytofirmans+ Trichoderma asperelloides (Cons3) in combinations with arbuscular mycorrhizal fungi (Rhizophagus irregularis), applied in the protective organic Minigran® formulations with or without additional application of the silicatic lignocellulose soil conditioner (Sanoplant®). At the end of a two-weeks recovery period from six weeks drought stress at a soil moisture level of 25% soil water holding capacity, all tested Minigran-Consortia formulations reduced the proportion of irreversibly drought-damaged leaves by 35-88%, irrespective of the soil conditioner treatments. Already the Minigran blank formulations had a certain beneficial effect on enzymatic (ascorbate peroxidase) and particularly non-enzymatic (total antioxidants) detoxification of reactive oxygen species (ROS), indicated by a significantly reduced ROS (H2O2) accumulation in the leaf tissue. This effect was further improved by introduction of the microbial consortia. Both, the Mingran blank formulations and the Minigran-consortia combinations, affected the hormonal status in the leaf tissue towards increased ABA/Gibberellic acid (GA) ratios and increased IAA levels, known to support tuber initiation and tuber growth and increased the jasmonic acid concentrations involved in abiotic stress signalling. The Minigran blank formulations also increased the root colonisation with AM fungi, which was further increased by introduction with the consortia, particularly in combination with the soil conditioner. Beneficial effects of the consortia on tuber biomass were mainly recorded in combination with the soil conditioner and even reached the values of well-watered controls with NPK fertilisation in case of Cons1. This was associated with a compensation of drought-induced reductions in P and K accumulation in the shoot tissue. Tuber quality was improved by increased starch concentrations with a simultaneous reduction of soluble sugars. The findings suggest that application of selected organic microbial consortia formulations in combination with silicatic soil conditioner has potential to improve the drought tolerance of potato and requires further investigation under field conditions.
Bio-effectors for improved growth, nutrient acquisition and disease resistance of crops
(2017) Weinmann, Markus; Neumann, Günter
Recent scientific approaches to sustain agricultural production in face of a growing world food demand, limited natural resources, and ecological concerns have been focusing on biological processes to support soil fertility and healthy plant growth. In this context, the use of “bio-effectors”, comprising living (micro-) organisms and active natural compounds, has been receiving increasing attention. In contrast to conventional fertilizers and pesticides, the effectiveness of “bio-effectors” is essentially not based on the substantial direct input of mineral plant nutrients, neither in inorganic nor organic forms, nor of a-priori toxic compounds. Their direct or indirect effects on plant performance are rather based on the functional implementation or activation of biological mechanisms, in particular those interfering with soil-plant-microbe interactions. The general objective of the present research work was to improve the empirical and conceptual understanding concerning the utilization of bio-effectors in agricultural practice, following the principles of plant growth stimulation, bio-fertilization and bio-control. One main aspect of investigation was the application of bio-effectors to improve the efficiency of phosphorus (P) acquisition by the plant. Promising bio-preparations based on microbial inoculants (e.g. Bacillus, Pseudomonas, Trichoderma species) as well as natural compounds (e.g. algae extracts, humic acids) were tested in screening assays, greenhouse, and field experiments to characterize their potential effectiveness under varying environmental conditions. The most significant effects on plants appeared under severely low phosphate availability, but even under controlled conditions, bio-effectors required a narrow range of conductive environmental settings to reveal their potential effectiveness. Another focus of research was the application of bio-effectors to control soil borne pathogens, which typically appear in unsound crop rotations. Emphasis was set on take-all disease in wheat induced by the fungus Gaeumannomyces graminis. While the effectiveness of oat precrops to control take-all in subsequent wheat has been attributed to microbial changes and enhanced manganese (Mn) availability in soils, the take-all fungus is known to decrease the availability of Mn by oxidation. Against this background, the effectiveness of oat precrops and alternative crop management strategies to improve the Mn status and suppress the severity of take-all in wheat was investigated under controlled and field conditions. In conclusion, none of the tested supplemental treatments, such the application of microbial bio-effectors, stabilized ammonium or manganese fertilizers, could fully substitute for the multiple effectiveness of oat precrops, which was further confirmed by the results of a field experiment. Finally, some general conclusions and perspectives are summarized. Selected bio-effectors showed a strong capacity to improve the nutrient acquisition and healthy growth of crop plants under controlled conditions, but not in field experiments. However, even under controlled conditions the strongest effects occurred when plants were exposed to abiotic or biotic stresses, such as severely limited P availability or pathogen infestation of the soil substrate, still restricting plant growth to unproductive levels. Facing this situation, there is no perspective to improve the field efficiency of promising bio-effectors applications as a stand-alone approach. The only chance to develop viable alternatives to the conventional use of fertilizers or pesticides, for an ecological intensification of agriculture that maintains high yield levels, seems to be a reasonable integration of bio-effectors into the whole crop management of sound agricultural practice.
Bioeffector products for plant growth promotion in agriculture
modes of action and the application in the field
(2021) Weber, Nino Frederik; Neumann, Günter
Modern agriculture faces a conflict between sustainability and the demand for a higher food production. This conflict is exacerbated by climate change and its influence on vegetation, ecology and human society. To reduce land use, the reduction of yield losses and food waste is crucial. Moreover a sustainable intensification is necessary to increase yields, while at the same time input of limited resources such as drinking water or fertilizer should be kept as low as possible. This might be achieved by improving nutrient recycling and plant resistance to abiotic or biotic stress. Bioeffectors (BE) comprise seaweed or plant extracts and microbial inoculums that may stimulate plant growth by phytohormonal changes and increase plant tolerance to abiotic stress (biostimulants), solubilize or mobilize phosphorus from sparingly soluble sources such as Al/Fe or Ca-phosphates in the soil, rock phosphates, recycling fertilizer or organic phosphorus sources like phytate (biofertilizer), or improve plant resistance against pathogens by induced-systemic resistance (ISR) or antibiosis (biocontrol). For this study, in total 18 BE products were tested in germination, pot and field experiments for their potential to improve plant growth, cold stress tolerance, nutrient acquisition and yield in maize and tomato. Additionally, a gene expression analysis in maize was performed using whole transcriptome sequencing (RNA-Seq) after the application of two potential plant growth promoting rhizobacteria (PGPR), the Pseudomonas sp. strain DSMZ 13134 “Proradix” and the Bacillus amyloliquefaciens strain FZB42. Seaweed products supplemented with high amounts of the micronutrients Zn and Mn were effective in reducing detrimental cold stress reactions in maize whereas microbial products and seaweed extracts without micronutrient supplementation failed under the experimental conditions. At optimal temperature the product containing the Pseudomonas sp. strain was repeatedly able to stimulate root and shoot growth of maize plants whereas in tomato only in heat-treated soil substrate significant effects were observed. Results indicate that the efficacy of the product was mainly attributed to stimulation or shifts in the soil microbial community. Additionally, the FZB42 strain was able to stimulate root and plant growth in some experiments whereas the effects were less reproducible and more sensitive to environmental conditions. Fungal BE products were less effective in plant growth stimulation and showed detrimental effects in some experiments. Under the applied experimental conditions BE-derived plant growth stimulation mainly was attributed to biostimulation but aspects of biofertilization or biocontrol cannot be excluded, as all experiments were conducted in non-sterile soil substrates. Root and shoot growth are stimulated in response to hormonal shifts. In the gene expression analysis only weak responses to BE treatments were observed, as previously reported from other studies conducted under non-sterile conditions. Nevertheless, some plant stress responses were observed that resembled in some aspects those reported for phosphorus (P) deficiency in others those reported for ISR/SAR. Especially the activation of plant defence mechanisms, such as the production of secondary metabolites, ethylene production and reception and the expression of several classes of stress-related transcription factors, including JA-responsive JAZ genes, was observed. It also seems probable that in plants growing in PGPR-drenched soils, especially at high application rates, a sink stimulation for assimilates triggers changes in photosynthetic activity and root growth leading to an improved nutrient acquisition. Nevertheless, due to the complexity of interactions in natural soil environments as well as under practice conditions, a designation of a distinct mode of action for plant growth stimulation by microbial BEs is not realistic. A comparison of the overall results with those reported in literature or other working groups in a common research project (“Biofector”) supported the often-reported low reproducibility of plant growth promotion effects by BE products under applied conditions. Factors that influenced BE efficacy were application time and rates, temperature, soil buffer capacity, phosphorus sources and nitrogen fertilization, light conditions and the soil microbial community. Results indicate that in maize cultivation seed treatment is the most economic application technique for microbial products whereas for vegetable or high-value crops with good economic benefit soil drenching is recommended. For seaweed extracts foliar application seems to be the most economic and efficient choice. Furthermore, results emphasize the importance of a balanced natural soil microflora for plant health and yield stability.
Biomass production for bioenergy as an interface between yield optimisation, ecology and human nutrition
a question of resource efficiency
(2012) Gauder, Martin; Claupein, Wilhelm
In this thesis, specific questions dealing with sustainability of bioenergy were analysed on regional scales. One focus was put on food security and the connections to bioenergy production. Therefore a study, based on the comprehensive range of information available, was conducted for ethanol production in Brazil. The second focus laid on Europe and the potentials and environmental risks which come along with bioenergy production. A study on interannual yield performance of long-term Miscanthus plantations was conducted to evaluate potentials and genotype diversities of Miscanthus cropping in Southwest Germany. To identify the possible contribution of by-products from agriculture, a third study dealt with amount and distribution of surplus straw in Southwest Germany. Environmental aspects were addressed in a field trial, which monitored trace gas fluxes from soils under different energy plants also in Southwest Germany. The last study examined the potential of establishing large-scale poplar plantations in Romania and how this could contribute to the regional energy security.
Biomass quality of miscanthus genotypes for different bioconversion routes
(2017) Iqbal, Yasir; Lewandowski, Iris
Currently, a wide range of biomass based resources (wood, agricultural residues, municipal waste, perennial dedicated energy crops) are being tested for different bioconversion routes such as combustion and ethanol production. In Europe, combustion is the most prevalent bioconversion route being adopted to produce heat and electricity. By 2020, in Europe out of 139 Mtoe biomass based energy production, 110.4 Mtoe will be heat and electricity. Along with combustion, EU (European Union) focuses on increasing the share of biofuels production to achieve the EU 2020 target to reach 10% share of renewables in the transportation sector. For both aforementioned bioconversion routes, large amount of feedstocks, produced in a sustainable way, are required. Miscanthus, being a perennial dedicated energy crop has the potential to deliver high yields by using the soil resources efficiently. However, the per unit energy yield depends not only on biomass yield but also quality of biomass relevant for a specific end use. For miscanthus based combustion, high lignin contents increase the energy yield of the biomass. The main challenges are high emissions (e.g. NOx) and combustion relevant problems such as corrosion, fouling and low ash melting temperature. Other than for combustion, the high lignin content is the main problem during miscanthus based ethanol production. Presently, M. x giganteus is the only commercially grown genotype, however a wide range of genotypes are being tested under the European conditions to select the most promising ones for both combustion and ethanol production. Therefore, the focus of this study is to evaluate the biomass quality of different miscanthus genotypes for combustion and ethanol production and relevant measures for each bioconversion route to optimize biomass quality at field level to fit the user demand. To realise the aim of this study, two different field trials were used: 1) long term field trial with 15 miscanthus genotypes (four M. x giganteus, one M. sacchariflorus, five M. sinensis hybrids and five M. sinensis genotypes) was established as randomized block design with three replications; 2) field trial with M. x giganteus and switchgrass was established as a randomized split plot design with different crops as main plots, divided into three subplots with different N levels (0, 40, and 80 kg N ha-1a-1). The biomass samples collected from these field trials were processed and analysed in laboratory to test the biomass quality parameters for combustion (mineral analysis, silicon, chloride, ash, moisture and ash melting behaviour) and ethanol production (fiber analysis, acid/base based pre-treatment). The outcomes of this study show that at biomass production level, crop management practices such as selection of appropriate genotypes, fertilization and time of harvesting determine the yield, biomass quality, overall cost of production and environmental performance of the crop for a specific bioconversion route (combustion, ethanol production). The ash melting behavior during combustion process can be improved through appropriate genotype selection from an ash deformation temperature of 800 °C up to 1100 °C. For ethanol production, fiber composition can be improved up to 16% through appropriate genotype selection by decreasing the lignin content and improving the cellulose content. This improvement will not be completely translated to increase in ethanol yield. However, it can improve the overall efficiency of conversion process by decreased the lignin content and subsequently lowering the energy and chemical inputs required for pre-treatment. In this study, no quantification is made about improvement in final ethanol yield. In fertilization, N fertilization is very important because it constituted up to 72% of the emissions in the conducted LCA described in chapter-1. Therefore, in case of high N fertilization, it not only affects the biomass quality but also increases the cost of biomass production and decreases the environmental performance of the crop. Based on the outcomes of this study, it can be concluded that at this location 40 kg N ha-1a-1 fertilization is sufficient to achieve good yield and quality biomass under late harvest regimes (March). At 40 kg N ha-1a-1 fertilization, the N content in the harvested biomass was still well below the threshold level set (0.3-1%) for biomass by the ENplus wood pellets. The other important factor which offers opportunity to optimize biomass quality is time of harvesting. Through appropriate harvesting time, biomass combustion quality can be improved up to 30% through decreasing the mineral, chloride and ash content whereas for ethanol production, fiber composition can be improved up to 12% by decreasing the lignin content. In practical terms, the delay in harvest will help to meet the set quality standards and counter the relevant challenges for each bioconversion route. In current study, none of the biomasses harvested from the different miscanthus genotypes, except for M. sinensis, could meet the ENplus-B wood pellet standards. For combustion, early ripening thin stemmed genotypes such as M. sinensis are recommended under late harvest regime (March). However, the low yield of these genotypes is a major concern because low biomass quantity decreases the final energy yield. Considering the high dry matter yield, cellulose and hemicellulose content, M. x giganteus and M. sacchariflorus are recommended for ethanol production under early harvest regimes (September-October). However, the high lignin content of M. x giganteus and M. sacchariflorus reduces the efficiency of overall process. Therefore, in this study recommendations were given to breeders about development of new genotypes for combustion by combining interesting traits such as high yield and lignin content of M. x giganteus, low ash content of M. sacchariflorus, low mineral content especially K and Cl of M. sinensis, whereas for ethanol production low lignin content of M. sinensis can be combined with high yield of M. x giganteus. This study suggests that optimization of biomass quality for a specific end use can be achieved through adoption of appropriate crop management practices such as selection of appropriate genotype and time of harvesting. This is the most cost-effective way with least environmental implications.
Biometrical tools for heterosis research
(2010) Schützenmeister, André; Piepho, Hans-Peter
Molecular biological technologies are frequently applied for heterosis research. Large datasets are generated, which are usually analyzed with linear models or linear mixed models. Both types of model make a number of assumptions, and it is important to ensure that the underlying theory applies for datasets at hand. Simultaneous violation of the normality and homoscedasticity assumptions in the linear model setup can produce highly misleading results of associated t- and F-tests. Linear mixed models assume multivariate normality of random effects and errors. These distributional assumptions enable (restricted) maximum likelihood based procedures for estimating variance components. Violations of these assumptions lead to results, which are unreliable and, thus, are potentially misleading. A simulation-based approach for the residual analysis of linear models is introduced, which is extended to linear mixed models. Based on simulation results, the concept of simultaneous tolerance bounds is developed, which facilitates assessing various diagnostic plots. This is exemplified by applying the approach to the residual analysis of different datasets, comparing results to those of other authors. It is shown that the approach is also beneficial, when applied to formal significance tests, which may be used for assessing model assumptions as well. This is supported by the results of a simulation study, where various alternative, non-normal distributions were used for generating data of various experimental designs of varying complexity. For linear mixed models, where studentized residuals are not pivotal quantities, as is the case for linear models, a simulation study is employed for assessing whether the nominal error rate under the null hypothesis complies with the expected nominal error rate. Furthermore, a novel step within the preprocessing pipeline of two-color cDNA microarray data is introduced. The additional step comprises spatial smoothing of microarray background intensities. It is investigated whether anisotropic correlation models need to be employed or isotropic models are sufficient. A self-versus-self dataset with superimposed sets of simulated, differentially expressed genes is used to demonstrate several beneficial features of background smoothing. In combination with background correction algorithms, which avoid negative intensities and which have already been shown to be superior, this additional step increases the power in finding differentially expressed genes, lowers the number of false positive results, and increases the accuracy of estimated fold changes.
Boron foliar fertilization: impacts on absorption and subsequent translocation of foliar applied Boron
(2012) Will, Silke; Müller, Torsten
Foliar fertilization is an agricultural practice to supply plants with a specific nutrient in times of low soil availability of the nutrient or low root activity, e.g. during generative growth. The focus of this study was placed on Boron (B). Boron is an essential micronutrient for higher plants and deficiency appears in many countries on numerous crops throughout the world. B fertilization is often applied as foliar fertilizer, but the efficiency is inconsistent. The possible physiological function of B in plants is described in Chapter 1 within the general introduction. The experiments were conducted on two disparate crop species (soybean and lychee) and the impact of different parameters on foliar B absorption and subsequent translocation was studied. The first study (Chapter 2) shows the impact of plant B status on foliar B absorption and subsequent translocation in soybean. The limited absorption of foliar applied B in B deficient plants was observed in soybean and in lychee. The physiological study was developed for soybean plants pre-treated with different B root supply, ranging from deficient to B intoxicated plants. In addition, different formulations were tested in order to increase the subsequent B translocation after foliar B absorption. For this reason polyols (mannitol, sorbitol) were added to the foliar formulations, as they form stable polyol borate ester with B and these compounds enable phloem mobility in some species. Lowest absorption was observed in plants with B deficiency and B intoxication, whereas the share of subsequent B basi translocation was highest. Results correlated with measurements on stomata opening and water potential. The interruption of the transpiration stream, indicated by high water potentials in B deficient and intoxicated plants, might facilitate B phloem translocation, as it was shown in recent publications. Absorption rates were increased in treatments with polyol supplementation, probably due to a humectants effect (lowering the DRH). Subsequent translocation could not be improved by the addition of polyols. In Chapter 3 the impact of leaf side of application and adjuvant supplementation on foliar B absorption and subsequent translocation was studied on lychee and soybean. The effect of the adjuvants CaCl2 and sorbitol as humectant adjuvants and mannitol and sorbitol as B-binding adjuvants were investigated. Both plant species differed greatly in total absorption rates. Boron absorption through the abaxial leaf side was more than three-fold (soybean) or seven-fold (lychee) higher than through the adaxial side The addition of adjuvants significantly enhanced the rate of B absorption in soybean, but had no effect on B absorption in lychee. The positive results of adjuvant supplementation in soybean might be attributed to the humectants effect. Subsequent translocation could not be increased in neither of the treatments. The results on foliar B absorption via the abaxial leaf surface in both species suggest a high demand for future research, e.g. techniques to spray the abaxial leaf surface. In Chapter 4 the focus was to assess the impact of different parameters on foliar B absorption and subsequent translocation in lychee. B solutions were applied on the adaxial versus the abaxial leaf surface of mature or immature leaves. In addition, nocturnal versus diurnal application was studied. Absorption was significantly increased after application to the abaxial leaf surface. The parameters leaf age and time of application did not affect absorption. Subsequent translocation of foliar absorbed B increased significantly after foliar application of B to mature in comparison to immature leaves. Nocturnal application of B resulted in significantly enhanced basipetal B translocation. The efficacy of foliar B fertilization can be limited in lychee, especially if only the adaxial leaf surface is targeted as it commonly occurs with the spraying techniques available in many lychee orchards. The practical implications of our results clearly show that B foliar sprays should be applied nocturnally to the abaxial leaf surface. In conclusion, absorption and subsequent translocation of foliar applied B can be increased by different parameters in lychee and soybean. Plant B status and leafside of application showed a strong impact on foliar B absorption. All results are discussed in Chapter 5.
The challenge to achieve a balanced fertilization management in intensive organic vegetable production – approaches for improvement
(2024) Stein, Sophie; Möller, Kurt
The nutrient supply – especially in stockless farms – is a major challenge for organic vegetable farms. Due to the lack of animal husbandry, the nutrient cycle within the farm is limited. At the same time, the nutrient flows in vegetable growing are very high due to the high nitrogen (N) and potassium (K) requirements of the crops. If the nutrient flows are not adapted to the needs of the crops, severe nutrient imbalances, yield or quality losses can occur. Fertilization with basic fertilizers such as manure or compost, based on the N-demand of the crops, can lead to an accumulation of phosphorus (P) in the soil in the long term. Fertilization with N-rich organic commercial fertilizers, on the other hand, is to some extent contradictory to the principles of organic farming due to their origin – mostly from conventional animal husbandry. Another possibility for the exclusive N supply of the farm is the targeted use of legumes with the ability for biological N-fixation (BNF). However, since the cultivation of fodder legumes or grain legumes plays a minor role in vegetable production without livestock, their use for fertilizer management is limited. The aim of this thesis was to optimize fertilizer management in vegetable production based on balanced nutrient budgets of the three main nutrients N, P and K, as well as to increase the supply of N within the farm through the N-fixation of legumes. In a farm survey, the status quo of nutrient management was determined and analyzed using nutrient budgets. In two systemic field trials, the contribution of the strategies legume winter cover crop and living mulch to the on-farm N supply was tested. The status quo of the budgets on organic vegetable farms without livestock shows average budget surpluses of 67.5 kg N ha-1, 2.06 kg P ha-1 and 0.26 kg K ha-1. Another result is that an increase in the N content of base fertilizers such as solid manure or champost leads to an increase in the P and K balance. In the long term, such a strategy carries the risk of nutrient enrichment in the soil. Strategies based on the use of large amounts of keratin fertilizers, on the other hand, have the opposite effect, namely a long-term depletion of P and K. The integration of legumes into the vegetable crop rotation shows that both strategies – leguminous winter cover crops as a preceding crop to white cabbage and leguminous living mulch in combination with white cabbage – lead to similar or even slightly higher cabbage yields than cultivation without legumes or green cover. The direct N-effect of the leguminous winter cover crop on the first crop of white cabbage is about 2/3 of the total N-effect, the N-effect on the second crop of winter wheat is about 1/3 of the total N-effect of the BNF. In the case of the living mulch biomass, which is only incorporated after cabbage cultivation, the direct N effect of BNF on the first main crop is less than 40 %. The N effect on the subsequent winter wheat crop is over 60 %. The results of this thesis show that organic vegetable farms face at least two major challenges in terms of nutrient management: They must implement nutrient management that ensures a balanced nutrient budget in the soil and on the farm while reducing N surpluses through more efficient use of internal and external N sources. This thesis provides important figures for the characterization and balancing of nutrient management in vegetable production. These figures can be used to address the challenge of balanced fertilization management.

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