Browsing by Subject "Plant nutrition"

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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.
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.
Combined effects of drought and soil fertility on the synthesis of vitamins in green leafy vegetables
(2023) Park, Taewan; Fischer, Sahrah; Lambert, Christine; Hilger, Thomas; Jordan, Irmgard; Cadisch, Georg
Green leafy vegetables, such as Vigna unguiculata, Brassica oleraceae, and Solanum scabrum, are important sources of vitamins A, B1, and C. Although vitamin deficiencies considerably affect human health, not much is known about the effects of changing soil and climate conditions on vegetable vitamin concentrations. The effects of high or low soil fertility and three drought intensities (75%, 50%, and 25% pot capacity) on three plant species were analysed (n = 48 pots) in a greenhouse trial. The fresh yield was reduced in all the vegetables as a result of lower soil fertility during a severe drought. The vitamin concentrations increased with increasing drought stress in some species. Regardless, the total vitamin yields showed a net decrease due to the significant biomass loss. Changes in vitamin concentrations as a result of a degrading environment and increasing climate change events are an important factor to be considered for food composition calculations and nutrient balances, particularly due to the consequences on human health, and should therefore be considered in agricultural trials.
Entwicklung innovativer Pflanzenschutzprodukte und -verfahren als umweltfreundliche Alternativen zur Bekämpfung von Mehltaupilzen : Bericht im Rahmen des Forschungsprojektes: „Silizium als Aktivator bei Kulturpflanzen“
(2019) Raupp, Manfred G.; Weinmann, Markus; Arbeitsgemeinschaft industrieller Forschungsvereinigungen „Otto von Guericke“ e. V. (AiF) Projekt GmbH, Berlin; Madora GmbH, Lörrach; Römheld, Volker; Neumann, Günter; Blaich, Rolf; Merkt, Nikolaus
Powdery mildews are among the most important diseases in many crop plants. In all sectors of crop production (agriculture, viticulture, horticulture and orchards) powdery mildew fungi can cause severe damage under field as well as greenhouse conditions. Although organic synthetic fungicides have been used to combat powdery mildews in conventional and integrated agriculture for decades, organic farming lacks effective alternatives to the ecologically questionable sulfur fungicides. Yet, also for integrated or conventional crop production, alternatives or supplements for a reduction and more effective use of synthetic fungicides would be desirable to optimize the production of high quality food with the help of environmentally friendly means. Objective of the present work was the development of innovative crop protection products and application strategies to combat powdery mildew fungi with respect to the knowledge on resistance-enhancing effects of an improved silicon (Si), manganese (Mn) and zinc (Zn) supply to the plants. Furthermore, various plant extracts have recently received renewed attention. Among other active natural agents, garlic (Allium sativum L.) is known for its fungitoxic effect and at the same time high Mn and Zn contents. With the present work, an overview of possible approaches to control powdery mildew in grapevine by use of Si, Mn, Zn and plant extracts from garlic has been elaborated in greenhouse experiments. In this regard, the physiological significance of Si, Mn and Zn for the expression and strengthening of plant own resistance mechanisms was distinguished from the effectiveness of spray applications for forming passive silicate crusts as mechanical infection barriers. The physiological Si status of the plants could be clearly improved only by soil rather than foliar application of silicates. Regarding the soil application of silicates, however, no practical applications are known, how silicon fertilizers can be distributed under field conditions in the soil and brought into the rhizosphere to continuously ensure high rates of Si uptake. There is also still considerable uncertainty whether the soil application of silicates in non-Si accumulators, such as grapevines, can result in sufficient Si uptake for an effective expression of resistance mechanisms. The most impressive effects in the control of powdery mildew were achieved with the spray application of potassium silicate in combination with wetting agents to form silicate crusts on the leaf surface. The positive influence of Mn and Zn on the effectiveness of spray applications of potassium silicate and the adequate compatibility of Mn and Zn chelates with potassium silicate suggest that the interactions between Si, Mn and Zn should be considered for further product development. The application of garlic extract did not result in sufficient efficiency, although protective and curative properties could be observed. Allicin, supposed to be the active ingredient of garlic extract, has a broad spectrum of antimicrobial activity and is one of the few agents for which no development of resistance has been found in microorganisms so far. Therefore, the interest in this agent for the development of biological plant protection products is expected to increase.
Environmental and farm management effects on food nutrient concentrations and yields of East African staple food crops
(2021) Fischer, Sahrah; Cadisch, Georg
Hidden hunger affects two billion people worldwide, particularly children and pregnant women. Human health and well-being are dependent on the quality and quantity of food consumed, particularly of plant-based foods. Plants source their nutrients from the soil. Essential nutrients for both, plants and humans, therefore, predominantly originate from the soil. Very little is known about the influence of environmental factors (e.g. soil types and abiotic factors, such as weather), or farm management choices (e.g. fertilisation or agrobiodiversity), on nutrient concentrations of edible crop parts. The main aim of this thesis was, therefore, to analyse the effects of soil fertility, farm management, and abiotic factors such as drought, on the quantity (yields) and quality (nutrient concentrations) of essential macro- (Mg, P, S, K, Ca) and micronutrients (Fe, Zn, Mn and Cu), of the edible parts of three East African staple food crops, i.e. maize (Zea mays L.), cassava (Manihot esculenta} Crantz), and matooke (East African Highland Banana (Musa acuminata Colla)), and discuss the resulting implications for food and nutrition security. Two research areas were selected in East Africa, one with a high fertility soil (Kapchorwa, Uganda - Nitisol) and one with a low fertility soil (Teso South, Kenya – Ferralsol). In each region, 72 households were randomly selected, and leaf and edible crop parts, and soil samples collected on three fields per household, organised by distance (closest, mid-distance, and farthest field). Maize and cassava were collected in Teso South, maize and matooke were collected in Kapchorwa. Yields, fertilizer usage and species richness (SR) and diversity (SD) were recorded per field. The total nutrient concentrations were measured in all samples collected (soils and plant parts). A drought occurring in the second rain season of 2016 provided the opportunity to analyse water stress effects on crop quantity and quality (Chapter 2). Edible part samples and yields collected in both seasons were compared. Soil chemical and physical properties, together with farm management variables, were compared to edible part nutrient concentrations and yields using a Canonical Correspondence Analysis (CCA) (Chapter 3). To understand the strength of association between the measurements routinely done by agronomists (leaf measurement) and nutritionists (edible part measurement), samples of each crop were collected, and were compared to each other and to yields, using a bivariate linear mixed model (Chapter 4). During the severe drought, nutrient concentrations in Kapchorwa decreased significantly from normal to drought season in both crops. In contrast, during the moderate drought in Teso South, nutrient concentrations increased significantly in both crops. Lacking nutrient phloem mobility is suggested to play a vital role in mobilisation of micronutrients (Fe, Mn, and Cu), as shown by their decreased concentration under severe drought in the yields of both crops in Kapchorwa (Chapter 2). Soil type had a very strong effect on food nutrient concentrations. Maize grain nutrient concentrations and yields, for example, were significantly higher for all nutrients measured on higher fertility soils. Maize grain had the highest correlations with soil factors. In contrast, corresponding correlations to management factors were much weaker (Chapter 3). Concerning the comparison of nutrient concentrations in different plant parts, low phloem mobile nutrients Ca, Mn, Fe, Zn, and Cu showed the largest differences in correlations between leaves and edible parts. In the same comparison, perennial crops (matooke and cassava) showed lower correlations between leaves and edible parts, than annual crops (maize) (Chapter 4). Environmental factors, such as drought impacted food nutrient concentrations. Severe drought caused a potential “double-burden” for consumers, decreasing both yields and nutrient concentrations, particularly of micronutrients. Considering food nutrient concentrations, apart from yield, as response variables in agronomic trials (e.g. fertilisation or soil improvement strategies) would contribute towards discounting the notion that crops growing on fertile soils always produce healthy and high-quality foods. Leaves may provide information on plant health, however, do not provide enough information to gauge both yields and food quality, particularly regarding micronutrients. The results also showed that measuring the edible part is vital to assessing food quality, particularly due to the observed effects of nutrient mobility, affecting particularly micronutrients and Ca. Ending hunger and improving food and nutrition security for all, particularly when confronted with global change issues such as degrading soils and a changing climate, requires a collaborative effort by all disciplines concerned.
Managing crop health by mineral nitrogen fertilization and use of different chemical nitrogen forms
(2023) Maywald, Niels Julian; Ludewig, Uwe
Maintaining plant health is one of the most difficult but crucial challenges in crop production to realize plants’ full genetic potential. It is lowered by a variety of abiotic and biotic stresses that are becoming more severe and unpredictable due to climate change and its consequences. In addition, the use of chemical synthetic pesticides is increasingly criticized for endangering sensitive natural resources and possible pesticide residues in food and environment. Avoiding or reducing the use of chemical synthetic plant protection products makes the control of phytopathogenic pests even more difficult. Therefore, in addition to optimizing various management measures such as tillage, sowing time, row spacing or crop rotation, mineral nitrogen (N) fertilization and the targeted application of N forms must be utilized to reduce abiotic stress factors and the infestation pressure of certain pests to ensure high yield performance. Consequently, several experiments were conducted to better understand how mineral nitrogen fertilization and forms can improve plant health by increasing plant resistance to abiotic stressors, particularly repeated drought stress and nutrient (P) deficiency, and to biotic stressors, such as relevant phytopathogenic fungi. It was found that with respect to repeated drought stress, maize plants receiving supplemental nitrogen during the recovery period after an early drought stress were better able to cope with late drought stress. In this context, N fertilization could help the plant to maintain its photosynthetic activity under drought stress. Additionally, plants repeatedly exposed to drought stress recovered faster with N fertilization due to transiently higher antioxidant levels and higher production of reactive oxygen species. A further experiment revealed that depending on the maize genotype, ammonium as a form of nitrogen has a positive effect on the availability and uptake of phosphorus compared to nitrate, depending on the maize genotype. This observation could be attributed not only to the acidifying effect on the pH of the rhizosphere, but also to the increased abundance of various phosphorus-solubilizing bacteria and arbuscular mycorrhizal fungi under ammonium nutrition. Together this could provide an enhanced P availability, which ultimately reduces plant stress and improves physiologically resistance leading to a reduction in disease risk. Nevertheless, studies revealed that high N fertilization in most cases promotes disease attack and makes the plant more susceptible to pathogens. Scrutinization of this observation indicated that N fertilization enhances infestations of biotrophic pathogens, especially in wheat, while necrotrophic fungi were attenuated. Overall, the complex relationship between plant pathogens and nitrogen nutrition appears to be highly variable due to dynamic factors such as the soil, microorganisms in the rhizosphere, environmental factors, and the host plant, making it difficult to give definite statements about the effects of nitrogen nutrition on pathogen occurrence. Thus, the form of nitrogen could be a promising way to target nitrogen fertilization against individual pathogens. With regards to the previous research, experiments on the influence of N form on pathogen infection, revealed that wheat leaves inoculated with the foliar pathogen Blumeria graminis f. sp. tritici (Bgt) were comparatively less infested when fertilized with nitrate or cyanamide compared to ammonium. After contact with the pathogen, an enhanced defense response in form of increased production of protective substances, indicated by increased concentrations of hydrogen peroxide and superoxide dismutase, and increased antioxidant potential, was detected. Further, it was observed that ammonium fertilization resulted in lower bacterial richness in the plant rhizosphere and higher fungal richness compared to nitrate supplementation. Additionally, a pronounced effect of ammonium fertilization on rootcolonization by important fungal pathogens such as Gaeumannomyces graminis var. tritici (Ggt) and Bgt was found. Regarding the experiment with maize under low P conditions, it appears that ammonium is able to promote both pathogenic and beneficial fungi in cereal crops. Thus, nitrate fertilization appears not only to suppress the occurrence of fungi, but may also promote pathogen-antagonistic bacteria, which in turn have a positive effect on fungal disease suppression.
Molecular regulation of components of root development and nutrient uptake in white lupin (Lupinus albus L.)
(2023) Olt, Philipp; Ludewig, Uwe
White lupin (Lupinus albus L.) is specially adapted to sites with low availability of plant-available phosphorus (P), which is of particular agricultural importance because of chemical P fixation in the soil and limited reserves of P fertilizer resources. With special root structures, the cluster roots (syn. proteoid roots), it considerably increases the root surface area and excretes root exudates such as anions of organic acids, which make it possible to release phosphate ions from poorly soluble phosphate compounds in the soil and make them available to plants. The characteristic structure of these cluster roots usually consists of a lateral root with certain sections that have a significantly higher density of further lateral roots (rootlets) than the rest of the lateral root. In addition, the rootlets are evenly limited in length and, as they grow bundled in the cluster sections, the structure of cluster roots is reminiscent of a bottle brush. Cluster roots are also formed by other plant species such as some species from the Proteaceae family, but in contrast to these slow- growing and perennial woody plants, white lupin with its short life cycle and small size is an ideal model organism for the study of these special root structures. In addition to the mechanisms involved in the function of cluster roots, the regulation of formation and development of cluster roots is also of great importance for basic research in this field. Three studies were carried out as part of this thesis to examine these aspects in more detail. In order to better understand the functional mechanisms involved in the excretion of exudates, the hypothesis that the METAL AND TOXIN EXTRUSION (MATE) transport proteins LaMATE and LaMATE3 transport citrate was tested in the first study. The similarity of the gene sequences of these white lupin proteins with proteins from the MATE/DTX family, of which citrate transport is already known, as well as the increased gene expression of LaMATE and LaMATE3 in mature cluster roots led to this assumption. However, electrophysiological studies of the proteins with 13C- labeled citrate showed that LaMATE and LaMATE3 probably do not transport citrate and also the analysis of root exudates from transient loss-of-function mutants could not confirm the involvement of LaMATE in the transport of citrate. However, the excretion of the isoflavonoid genistein was found to be significantly reduced in the transient loss-of-function mutants, leading to the hypothesis that LaMATE may be involved in the exudation of isoflavonoids in mature cluster roots. As a result of the mobilization of phosphates through the excretion of organic acids, other cations such as manganese (Mn) also dissolve, which leads to increased Mn concentrations in the soil solution. As manganese uptake in the roots is not actively regulated, Mn accumulates in the plant, which has a toxic effect in higher concentrations. For this reason, white lupin needs a strategy to counteract toxic manganese accumulation, which was investigated in more detail in the second study. The observation that a greater increase in Mn concentration could be measured in the leaves than in the roots after elevated Mn exposure of white lupin indicates an actively regulated transport of excess Mn in the plant. The METAL TOLERANCE PROTEIN (MTP) AtMTP8 is involved in the detoxification of excess Mn in Arabidopsis and the increased gene expression of the corresponding white lupin homolog LaMTP8.1 in plants exposed to elevated Mn concentration suggested that LaMTP8.1 also fulfills a detoxification function. In further experiments, the ability of the LaMTP8.1 protein to transport Mn was demonstrated by heterologous expression of LaMTP8.1 in yeast cells. Furthermore, the high Mn concentrations in the leaves already indicated that the sink of Mn sequestration is located there and since AtMTP8 transports Mn into the vacuole, it was assumed that LaMTP8.1 could be localized in the tonoplast of the leaf cells to transport excess Mn into the vacuoles. This hypothesis was confirmed by homologous expression of LaMTP8.1 combined with a fluorescent marker in white lupin protoplasts. In summary, this study demonstrated that LaMTP8.1 is a vacuolar Mn transporter that mediates the transport of Mn into the vacuoles of leaf cells to detoxify excess Mn. While the first two studies addressed functional and physiological aspects of cluster roots, the third study focused on the mechanisms of formation and development of these root structures. To this end, the main focus was on the CLAVATA3/ EMBRYO SURROUNDING REGION (ESR)- RELATED (CLE) peptide family, of which some members regulate root growth in other plant species and enable more precise control of regulation compared to the known growth regulators auxin and cytokinin. In a comprehensive analysis, 30 known and further 25 new, putative CLE peptides were identified in Lupinus albus. Several of the CLE peptides were tested in a hydroponic system on young white lupins for their effects on root development and cluster root formation. The two CLE peptides LaCLE35 (RGVHyPSGANPLHN) and LaCLE55 (RRVHyPSCHyPDPLHN) showed striking inhibitory effects and altered both root growth and cluster root development in an inhibitory manner. The peptide LaCLE35 stood out in particular because it was the only CLE peptide detected in white lupin xylem sap and was therefore investigated in more detail. It was shown that LaCLE35 influences both the density and the length of cluster rootlets, and thus has an effect on the two crucial factors of cluster root formation. The inhibitory effect of CLE35 could be attributed to a suppression of cell elongation and further experiments with split-root setups showed that the externally added synthetic peptide LaCLE35 has a local but not a systemic effect. The investigations of the LaMATE transport proteins and LaMTP8.1-mediated Mn detoxification as well as the overview of the detected CLE peptides in white lupin and the analysis of the inhibitory influences of LaCLE35 on cluster roots form the basis of this thesis and aim to contribute to the understanding of the function, effects and formation of these special root structures.
Nitrogen improves the recovery of maize plants under repeated drought stress
(2022) Maywald, Niels Julian; Hernández‐Pridybailo, Andrés; Ludewig, Uwe
Background Modern high-yielding crops, such as maize, are characterized by extensive yield stability across various environments and can cope with repetitive periods of moderate water shortage. However, there is conflicting evidence on how the nutritional status of the plants contributes to stress resilience and whether farmers have management options via nitrogen fertilization. Aims We aimed at identifying factors relevant for improved growth recovery of maize after repeated water deficit stress (WDS). Methods A pot experiment with maize and repeated WDS was conducted. Growth and recovery from stress and physiological parameters were measured. Results The growth penalty of juvenile maize plants exposed to a moderate WDS was lost after additional exposure to a 2-week WDS. Primed plants transiently contained more osmolytes and performed superior in the second recovery phase when nitrogen fertilization was applied directly before the second WDS. Nitrogen fertilization did not affect the osmolyte quantity, and primed plants had transiently higher antioxidant levels, higher reactive oxygen species production and recovered more quickly with N addition. Conclusions Pot experiments suggest that nitrogen fertilization may be an option to improve maize resilience to repeated WDS, a hypothesis that should be tested more rigorously in the field.