Browsing by Subject "Nitrogen"

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Ammonium fertilization increases the susceptibility to fungal leaf and root pathogens in winter wheat
(2022) Maywald, Niels Julian; Mang, Melissa; Pahls, Nathalie; Neumann, Günter; Ludewig, Uwe; Francioli, Davide
Nitrogen (N) fertilization is indispensable for high yields in agriculture due to its central role in plant growth and fitness. Different N forms affect plant defense against foliar pathogens and may alter soil–plant-microbe interactions. To date, however, the complex relationships between N forms and host defense are poorly understood. For this purpose, nitrate, ammonium, and cyanamide were compared in greenhouse pot trials with the aim to suppress two important fungal wheat pathogens Blumeria graminis f. sp. tritici (Bgt) and Gaeumannomyces graminis f. sp. tritici (Ggt). Wheat inoculated with the foliar pathogen Bgt was comparatively up to 80% less infested when fertilized with nitrate or cyanamide than with ammonium. Likewise, soil inoculation with the fungal pathogen Ggt revealed a 38% higher percentage of take-all infected roots in ammonium-fertilized plants. The bacterial rhizosphere microbiome was little affected by the N form, whereas the fungal community composition and structure were shaped by the different N fertilization, as revealed from metabarcoding data. Importantly, we observed a higher abundance of fungal pathogenic taxa in the ammonium-fertilized treatment compared to the other N treatments. Taken together, our findings demonstrated the critical role of fertilized N forms for host–pathogen interactions and wheat rhizosphere microbiome assemblage, which are relevant for plant fitness and performance.
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.
Combining remote sensing and crop modeling techniques to derive a nitrogen fertilizer application strategy
(2020) Röll, Georg; Graeff-Hönninger, Simone
The crucial question in this thesis was how can remote sensing data and crop models be used to derive a N fertilizer strategy that is capable to lower the environmental side effects of N fertilizer application. This raised the following detailed objectives: The first objective (i) how N content determination via spectral reflectance is influenced by different leaves and positions on the leaf was investigated in Publication I. Different wheat plants were cultivated under different N levels and under drought stress in two hydroponic greenhouse trials. Spectral reflectance measurements were taken from three leaves and at three positions on the leaf for each plant. In total, 16 vegetation indices broadly used in the literature were calculated based on the spectral reflectance for each combination of leaf and position. The plant N content was determined by lab analyses. Neither the position on the leaf nor leaf number had an impact on the accuracy of plant N determination via spectral reflectance measurements. Therefore measurements taken at the canopy level seem to be a valid approach. However, if other stress symptoms like drought or disease infection occur, a differentiation between leaves and positions on the leaf might play a more crucial role. Publication II dealt with the second objective on (ii), how to incorporate leaf disease into the DSSAT wheat model to enable the simulation of the impact of leaf disease on yield. An integration of sensor information in crop growth models requires the update of model state variables. A model extension was developed by adding a pest damage module to the existing wheat model. The approach was tested on a two-year dataset from Argentina with different wheat cultivars and on a one-year dataset from Germany with different inoculum levels of septoria tritici blotch (STB). After the integration of disease infection, the accuracy of the simulated yield and leaf area index (LAI) was improved. The Root mean squared error (RMSE) values for yield (1144 kg ha−1) and LAI (1.19 m2 m−2) were reduced by half (499 kg ha−1) for yield and LAI (0.69 m2 m−2). A sensitivity analysis also showed a strong responsiveness of the model by the integration of different STB disease infection scenarios. Increasing the modeling accuracy even further a MM approach seems to be suitable. Assembling more models increases the complexity of the simulation and the involved calibration procedure especially if the user is not familiar with all models. To avoid these conflicts, Publication III evaluated the third objective (iii) if an automatic calibration procedure in a MM approach for winter wheat can eliminate the subjectivity factor in model calibration. The model calibration was performed on a 4-yr N wheat fertilizer trial in southwest Germany. The evaluation mean showed satisfying results for the calibration (d-Index 0.93) and evaluation dataset (d-Index 0.81). This lead to the fourth (iv) objective to use a MM approach to improve the overall modeling accuracy. The evaluation of a fertilizer trial showed an improved modeling accuracy in most cases, especially in the drought season 2018. Based on the combination of a MM approach and the incorporation of sensor data, a Nitrogen Application Prescription System (NAPS) was developed. The initial NAPS setup requires long term recorded data (yield, weather, and soil) to ensure proper MM calibration. After calibration, the current growing season conditions are required (weather, management information) until the N application date. Afterward, the NAPS incorporates remote sensing information and generated weather for running future N application scenarios. The selection of the proper amount of N is determined by economic and ecological criteria. Furthermore, in order to account for differences in in-field variabilities and to deliver a N prescription site-specifically, the NAPS concept has to be applied on a geospatial scale by adjusting soil parameters spatially. The NAPS concept has the potential to adjust the N application more economically and ecologically by using current sensor data, historical yield records, and future weather prediction to derive a more precise N application strategy. Finally, this concept exhibits the potential for reconciliation of the issue of an economic, agricultural production without harming the environment.
Evaluation and improvement of N fertilization strategies in the wheat/maize double-cropping system of the North China Plain
(2015) Hartmann, Tobias Edward; Müller, Torsten
The North China Plain (NCP) is the main production area of cereal crops in China. The intensification of agricultural systems and the increased use of chemical N fertilizers are contributing to environmental pollution. One of the objectives of this thesis was to apply an Nmin based approach for the calculation of N application rates to a previously over-fertilized farmers field of the NCP and to evaluate the potential of reducing N inputs while maintaining the grain yield of a summer-maize/winter-wheat double-cropping system; and to evaluate fertilizer strategies, aiming to reduce N inputs and loss. Using an Nmin based approach for the calculation of fertilizer application rates, a reduction of fertilizer input by up to 50% compared to farmers practice (550 kg N ha-1 a-1) is possible without negatively affecting the grain yield of a wheat / maize double cropping system. The extreme re-supply of N during the summer-vegetation periods of maize in the first two experimental seasons resulted in high yields of the control treatment (CK: 2009: 5.7 and 2010: 5.9 Mg ha-1), which did not significantly differ from the fertilized treatments. This resulted in a reduced recovery efficiency of N (REN: 0.09 kg kg-1 – 0.30 kg kg-1). According to the results of this field experiment there was no agronomic justification for the application of fertilizer N. The grain yield of maize of the control treatment finally decreased in the third vegetation period of summer-maize. While maintaining the yield level, the optimized application of N increased REN (0.37 – 0.58 kg kg-1) significantly compared to farmers practice (0.21 kg kg-1) in this final vegetation period of maize. Wheat, in contrast to maize, is dependent on the application of fertilizer N for yield formation. In both vegetation periods of wheat, REN of the reduced treatments (0.34 – 1.0 kg kg-1) was significantly higher compared to FP (0.26 and 0.27 kg kg-1). The highest cumulated (5 vegetation periods) agronomic efficiency of N, as well as cumulated grain yield of the wheat/maize double-cropping system was observed when ammoniumsulphate-nitrate was applied in combination with the nitrification inhibitor 3,4-dimethylpyrazolephosphate (ASNDMPP: AEN: 19 kg kg-1, yield: 35 Mg ha-1) and according to crop N demand and residual soil mineral N. The highest REN was observed when urea ammonium nitrate was applied in a shallow, banded depot (UANDEP: 40 kg kg-1). The results of this field experiment further show that the N surplus (fertilized N - grain N) as well as the N balance (N Input - N output) after harvest are significantly lower when an optimized approach to fertilizer application is followed. The over-application of N for an optimized application of urea or ASNDMPP (Surplus: -25kg to 98 kg N ha-1; Balance: -36 to 102 kg N ha-1) was significantly reduced compared to current farmers practice (Surplus: 156kg to 187 kg N ha-1; Balance: 56 to 262 kg N ha-1). This leads to lower residual N in the soil horizon from 0 - 90 cm in the reduced treatments (113 kg N ha-1 at end of experiment) compared to FP (293 kg N ha-1). The results of this experiment indicate that N contained in the residues of maize is available only to the subsequent summer-crop and may sufficiently supply N for the yield formation of maize. Should the over-application of N be effectively reduced in the cropping systems of the NCP it is therefore necessary to take the N mineralization potential of soils into account. Based on the results of this field experiment and others, a crop-soil interface model (HERMES) was calibrated and validated to the conditions of the NCP. Finally, this research observed the effect of wheat straw and the urease inhibitor (UI) N-(n-buthyl) thiophosphoric triamide (nBPT) on the turnover of urea, as well as the loss of ammonia and nitrous oxide from an alkaline soil of the NCP. UI inhibit or reduce the appearance of ammonia after the application of urea and almost completely prevent the loss of N as ammonia (urea: 12 – 14% loss). nBPT effectively reduces the rate of urea hydrolysis but does not down-regulate the process enough to completely inhibit nitrification, thereby maintaining the availability of N from urea for plants. Further, the addition of wheat straw prolongs the appearance of ammonium after the application of urea while the appearance of nitrate is reduced. Wheat straw may therefore either act as a stimulant of hydrolysis or as an inhibitor of nitrification. The addition of urea increases soil respiration and the emission of N2O drastically, possibly acting as a C and N source for microbial organisms and causing a priming effect on microbial activity in soils. This effect was increased further when wheat straw as well as urea were added to soil. nBPT, in contrast, prevents a significant increase in CO2-respiration and N2O-emission. The urease inhibitor may therefore generally restrict microbial activity or shift nitrification/denitrification processes towards the emission of N2.
Fermentations- und Syntheseleistung der mikrobiellen Gemeinschaft des Pansens in vitro bei Variation der Grobfutter- und Stickstoffquellen
(2017) Zuber, Karin Helga Renate; Rodehutscord, Markus
In the first part of this doctoral thesis five batches of maize silage (MS), five batches of grass silage (GS) and three batches of alfalfa silage were incubated in the Hohenheim gas test. The variation of silages based on in vitro gas production kinetics and ammonia-nitrogen-concentration (NH3-N-concentration) in the mixture of rumen liquid and buffer solution over time was determined. For this purpose, 10 glass syringes per silage batch were used per experimental run. 3 glass syringes were used to determine the gas volume over 72 hours. The remaining 7 glass syringes were removed from the incubator at 7 time points and the NH3-N-concentration in the mixture of rumen liquid and buffer solution was determined. Upon the incubation of the 13 silages both silage species and batch had an influence on the potential gas production and on the rate constant of gas production. The determined potential gas production was between 62.5–74.2, 56.0–64.9 and 39.9–59.6 mL/200 mg organic matter (OM) for MS, GS and alfalfa silages. The rate constant of gas production amounted to 5.5–7.3, 3.8–7.1 and 5.0–7.7 %/h for MS, GS and alfalfa silages. Both silage species and batch as well as the time point and their interactions had an influence on the NH3-N-concentration in the mixture of rumen liquid and buffer solution. In the second part of this work one MS and one GS were incubated in the rumen simulation Rusitec. The influence of the forage source without supplementation of concentrates on the NH3-N-concentration in fermenter liquids over time and the fermentation and synthesis characteristics of the ruminal microbial community were investigated in vitro. Degradation of nutrients, gas, methane and short chain fatty acid (SCFA) production as well as NH3-N in effluent and microbial protein synthesis (MPS) were measured. The NH3-N-concentration in fermenter liquids was determined at different time points within two periods. Upon the incubation of GS, degradation of OM and fibre fractions, amount of NH3-N in the effluent as well as MPS and its efficiency (EMPS) was higher than with incubation of MS. Degradation of crude protein (CP) and total amount of SCFA were unaffected by silage. N-efficiency was higher with incubation of MS than with incubation of GS. During period 1, NH3-N-concentration in fermenter liquids increased for all treatments within the first 24 hours and was not different between the treatments. For GS, NH3-N-concentration subsequently continued to rise up to a maximum value at the last time point of measurement in period 1. NH3-N-concentrations in fermenter liquids in period 2 remained on a relatively constant level for MS and GS, differing between the two silages at all five time points of measurement. Mean NH3-N-concentration in fermenter liquids measured in period 2 corresponded in level with NH3-N-concentration determined in the effluent of both silages. In the third part of this work, the influence of different N-supplements to MS compared to GS on fermentation and synthesis characteristics of the ruminal microbial community in vitro was investigated. GS and MS were incubated in a Rusitec, the latter being either unsupplemented or supplemented with urea, pea protein, pea peptone or a mixture of amino acids to adjust N-content of MS to that of GS. The NH3-N-concentration in fermenter liquids was determined 0, 2, 4, 12 and 24 hours after changing the feed bag on day 12. Results concerning degradation of OM, CP and N-free extracts showed a positive influence of N-supplementations except for MS+pea protein. Furthermore, degradation of detergent fibres were partially improved through N-supplementations. The values of MPS and EMPS were enhanced through all N-supplementations. Thereby supplementation of urea and pea peptone to MS resulted in the largest increase in EMPS. However, through none of the N-supplements the level of GS in EMPS could be achieved. The determined course of NH3-N-concentration in fermenter liquids was largely similar between the treatments. Variation in nutrient composition of MS, GS and alfalfa silages were reflected in a large variation both in gas production kinetics and curve shape of NH3-N-concentration in the mixture of rumen liquid and buffer solution. Upon the sole incubation of MS and GS in the Rusitec, GS promoted MPS and EMPS stronger than MS. Supplementation of MS with different N-sources resulted in an increase in MPS and EMPS compared to MS without N-supplementation. Thus the assumption of an insufficient N-supply of ruminal microbes during the sole incubation of MS in vitro was confirmed. However, through none of the N-supplementations level of GS in EMPS could be achieved.
The functional diversity of the high-affinity nitrate transporter gene family in hexaploid wheat: Insights from distinct expression profiles
(2023) Sigalas, Petros P.; Buchner, Peter; Kröper, Alex; Hawkesford, Malcolm J.
High-affinity nitrate transporters (NRT) are key components for nitrogen (N) acquisition and distribution within plants. However, insights on these transporters in wheat are scarce. This study presents a comprehensive analysis of the NRT2 and NRT3 gene families, where the aim is to shed light on their functionality and to evaluate their responses to N availability. A total of 53 NRT2s and 11 NRT3s were identified in the bread wheat genome, and these were grouped into different clades and homoeologous subgroups. The transcriptional dynamics of the identified NRT2 and NRT3 genes, in response to N starvation and nitrate resupply, were examined by RT-qPCR in the roots and shoots of hydroponically grown wheat plants through a time course experiment. Additionally, the spatial expression patterns of these genes were explored within the plant. The NRT2s of clade 1, TaNRT2.1-2.6, showed a root-specific expression and significant upregulation in response to N starvation, thus emphasizing a role in N acquisition. However, most of the clade 2 NRT2s displayed reduced expression under N-starved conditions. Nitrate resupply after N starvation revealed rapid responsiveness in TaNRT2.1-2.6, while clade 2 genes exhibited gradual induction, primarily in the roots. TaNRT2.18 was highly expressed in above-ground tissues and exhibited distinct nitrate-related response patterns for roots and shoots. The TaNRT3 gene expression closely paralleled the profiles of TaNRT2.1-2.6 in response to nitrate induction. These findings enhance the understanding of NRT2 and NRT3 involvement in nitrogen uptake and utilization, and they could have practical implications for improving nitrogen use efficiency. The study also recommends a standardized nomenclature for wheat NRT2 genes, thereby addressing prior naming inconsistencies.
Improved prediction of dietary protein use and nitrogen excretion in tropical dairy cattle
(2023) Salazar‐Cubillas, Khaterine; Dickhöfer, Uta
The overall objective of the present doctoral thesis was to evaluate the adequacy (i.e., accuracy and precision) of existing laboratory methodologies and modeling tools, originally designed for temperate systems, in predicting the nitrogen (N) supply and excretion of cattle in tropical husbandry systems. It was hypothesized that the adoption of laboratory methodologies and modeling tools from temperate systems without validating and adapting them for tropical systems may result in inaccurate estimations of N supply, utilization, and excretion, which will hamper the assessment of N use efficiency. An in vitro study was conducted to evaluate the adequacy of the chemical method (Sniffen et al., 1992; Kirchhof et al., 2010; Valdés et al., 2011) to predict rumen-undegraded crude protein (RUP) of tropical forages grasses and legumes (n = 23). The adequacy of the predictions was assessed by comparing them with RUP proportions measured in situ at rumen passage rates of 2, 5, and 8% per hour. Results showed that the RUP of tropical forages estimated with the in situ method can be predicted using the chemical method. However, regression equations developed for temperate forages were not adequate enough to predict RUP proportions of tropical forages consistently for all rumen passage rates. Instead, developed equations in the present thesis can be used to predict RUP proportion of tropical forages with a similar chemical composition than the reference forage sample set. A second in vitro study was conducted to evaluate the adequacy of the chemical (Sniffen et al., 1992; Zhao and Cao, 2004) and in vitro methods (Steingaß et al., 2001) to predict post-ruminal crude protein (PRCP) supply of tropical forages (n = 23). The adequacy of the PRCP supply with the chemical and in vitro methods were tested against PRCP supply estimated from in situ measurements at rumen passage rates of 2, 5, and 8% per hour and digested organic matter. Results showed that the in vitro method can be used as an alternative method to estimate PRCP supply in tropical forages at moderate to fast rumen passage rate but not at slow rumen passage rate. Available regression equations developed for temperate forages were not adequate enough to predict the PRCP supply of tropical forages from concentrations of chemical crude protein fractions. Instead, developed equations in the present thesis can be used to estimate PRCP supply of tropical forages with a similar chemical composition than the reference forage sample set. A third study was conducted to assess the adequacy of modeling tools to predict N excretion of cattle in tropical husbandry systems. These models, namely model A (based on AFRC, 1993), model G (based on GfE, 2001), and model I (INRA, 2019), were selected to predict fecal N (FN), urine N (UN), and total N (TN) excretion as well as FN fractions of dairy cows, heifers, and steers kept under typical tropical husbandry conditions. The adequacy of the model predictions was assessed against reference values of UN (total collection and creatinine method) and FN excretion (total collection, internal and external markers) (n = 392 observations). Adjustments were made to the models with the greatest potential to predict N excretion. The adjustments were focused on the input variables driving the variability in N excretion predictions, identified through a sensitivity analysis. None of the tested models predicts adequately the excretion of UN, FN, and of different FN fractions of individual cattle kept under tropical conditions. Instead, model I in the present thesis, adjusted for increased efficiency of rumen microbial crude protein synthesis and reduced intercept of FN prediction, can be used to estimate FN and TN excretion of individual cattle kept under tropical conditions. The findings from the present thesis partially support our hypothesis. The adjustment of laboratory methodologies, such as the chemical method used to estimate the protein value of temperate forages, to tropical forages, results in more adequate estimates of the proportion of RUP and PRCP supply of tropical forages. Model I is, therefore, able to predict the N excretion of cattle more adequately in tropical husbandry systems, because it is sensitive to differences in the RUP proportion and PRCP supply. In addition to increasing the adequacy of these input variables, adjustments made to the microbial protein synthesis and intercept of the FN excretion of model I results in a more adequate prediction of N excretion by cattle in tropical husbandry systems. However, not all adjustments to laboratory methodologies and modeling tools from temperate systems yielded adequate predictions. Specifically, challenges remained in predicting RUP proportion and PRCP supply for tropical forage legume with slow rumen passage rates, as well as urinary N excretion in cattle with low N intakes. Consequently, further research is required to identify the factors contributing to their poor adequacy.
Interactions of nitrogen-related, growth promoting bacteria with Miscanthus × giganteus : impact and mechanism
(2020) Liu, Yuan; Ludewig, Uwe
The highly nitrogen-use efficient biomass grass Miscanthus is a host of the bacterial endophyte Herbaspirillum frisingense. While Herbaspirillum frisingense has the genetic competence to fix nitrogen, the plant-associated microbiome may also contribute to this nitrogen efficiency. Furthermore, the costly field establishment of the sterile perennial Miscanthus × giganteus from rhizomes is a severe constraint for expanding the production area of this commercial biomass crop. In this study, the effect of Herbaspirillum frisingense inoculation on stem-cutting sprouting, shoot biomass and other yield parameters was investigated. I studied how the inoculation impacts on the M. × giganteus associated microbiome and how the long term differences in nitrogen fertilizer amount modulated the M. × giganteus associated microbiome. This was studied in a 14 year-old field trial of M. ×giganteus fertilized with various amounts of nitrogen. Stem cutting inoculation improved the shoot sprouting and establishment success of Miscanthus × giganteus in the greenhouse. In a small field trial, plant height and biomass from inoculated sites were significantly larger in the second year after establishment, but already after one year after inoculation, the bulk soil, rhizosphere, root and rhizome microbiomes were almost devoid of Herbaspirillum. This beta-proteobacterium may colonize the shoot of Miscanthus × giganteus more efficiently. Major differences between bacterial communities were determined by plant-soil compartments and less by the plant organs, while both inoculation and nitrogen had little effects on these communities. Compared to the little effect on the soil, rhizosphere and root microbiomes, the rhizome microbiome was massively modulated by both inoculation and nitrogen level. In the rhizome, several proteobacteria, which are associated with plant growth promoting functions, were enriched by inoculation, while N2-fixing-related bacterial families were favored by long-term nitrogen-deficiency plots, but denitrifier-related families were depleted. The studies suggest that H. frisingense inoculation may improve establishment of Miscanthus stem cuttings and has long-lasting effects on the rhizome microbiome diversity, despite low rhizocompetence and low root abundance. Meanwhile, the rhizome could be a potential nitrogen fixation factory. The organ-specific, nitrogen-related bacterial communities are modulated by long-term different nitrogen supply and are mainly shaped by the plant, which provides guidance for optimizing Miscanthus sustainable cultivation.
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.
Microbial consortia versus single-strain inoculants as drought stress protectants in potato affected by the form of N supply
(2024) Mamun, Abdullah Al; Neumann, Günter; Moradtalab, Narges; Ahmed, Aneesh; Dupuis, Brice; Darbon, Geoffrey; Nawaz, Fahim; Declerck, Stephane; Mai, Karin; Vogt, Wolfgang; Ludewig, Uwe; Weinmann, Markus
This study investigated the drought protection effects of six fungal and bacterial inoculants and ten consortia thereof on vegetative growth, nutritional status, and tuberization of potato under controlled and field conditions. It was hypothesized that microbial consortia offer improved drought protection as compared with single strains, due to complementary or synergistic effects, with differential impacts also of N fertilization management. Under NO3− fertilization, a 70% reduction in water supply over six weeks reduced shoot and tuber biomass of non-inoculated plants by 30% and 50%, respectively, and induced phosphate (P) limitation compared to the well-watered control. 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 fungus (AMF) inoculant Rhizophagus irregularis MUCL41833 (five cases) and stimulation of root growth (five cases). Additionally, Bacillus amyloliquefaciens FZB42 and AMF + Pseudomonas brassicacearum 3Re2-7 significantly reduced irreversible drought-induced leaf damage after recovery to well-watered conditions. However, the microbial inoculants did not mitigate drought-induced reductions in tuber biomass, neither in greenhouse nor in field experiments. By contrast, NH4+-dominated fertilization significantly increased tuber biomass under drought stress (534%), which was further increased by additional AMF inoculation (951%). This coincided 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, involved in drought stress signaling and tuberization, and (iv) reduced irreversible drought-induced leaf damage. Additional application of bacterial inoculants further improved ROS detoxification by increasing the production of antioxidants but stimulated biomass allocation towards shoot growth at the expense of tuber development. The results demonstrated that microbial consortia could increase the probability of drought protection effects influenced by the form of N supply. However, protective effects on vegetative growth do not necessarily translate into yield benefits, which can be achieved by adequate combination of inoculants and fertilizers.
Nitrous oxide emissions and mitigation strategies in winter oilseed rape cultivation
(2019) Kesenheimer, Katharina Anne; Müller, Torsten
After carbon dioxide and methane, nitrous oxide, is the third most important greenhouse gas in the atmosphere. Nitrous oxide contributes to the greenhouse gas effect as well as to ozone depletion. The major portion of anthropogenic N2O emissions are stimulated by the use of nitrogen fertilizers in agriculture. The main processes for N2O production in soils are nitrification and denitrification. Various environmental and management factors such as precipitation, soil type, tillage, and crop residues affect these processes. N2O emissions can occur substantially in the post-harvest period. In Germany, approximately 50 % of the annual N2O emissions can occur during winter. This exhibits the importance and necessity of annual data sets which prevent misinterpretations instigated by investigations limited to the vegetation period. Winter oilseed rape is the most important raw material for biodiesel in Germany. As of 2018, the framework of the European Renewable Energy Directive requires that the use of biofuels achieve GHG savings of at least 50 % compared to fossil fuels. Feedstock production for biodiesel contributes more than half of the total GHG emissions. To close the nutrient cycle with renewable energy, digestate from biogas plants can be used as a substitute for mineral N fertilizer permitting the reduction of GHG emissions in the production process of synthetic fertilizers. When compared to other crops, OSR has a high N demand. The low N removal by the seeds results in inefficient use of nitrogen and therefore a high N surplus in the soil which is susceptible to gaseous or leaching losses to the environment. Another potential risk for N2O losses are crop residues after harvest. The type of soil cultivation can have both positive and negative implications on N2O emissions which depend, among other things, on tillage depth, soil type and moisture. Results from studies measuring N2O emissions from different tillage systems are contradicting and site dependent. This study aims to investigate the effect of (a) N fertilization (mineral and organic), (b) nitrification inhibitors, (c) crop residues and (d) tillage on direct N2O emissions and, inter alia, yield and soil nitrogen dynamics in OSR production. N2O emissions were monitored for three years over a range of N fertilization levels at five study sites chosen so as to best represent typical winter oilseed rape production in Germany. Furthermore, the effect of the nitrification inhibitor (NI) TZ+MP (1H-1,2,4-triazole and 3- methylpyrazole) with digestate is investigated. Additional experiments for 15N labelled crop residues, nitrification inhibitor DMPP (3,4-dimethylepyrazole phosphate) with mineral fertilizer and soil tillage were implemented. A high spatial and temporal variability in N2O fluxes over all sites was observed. At each site, increased N2O fluxes were often detected after N fertilization in conjunction with rainfall events. During the first six weeks after harvest we frequently observed increased N2O fluxes following rainfall. In this postharvest period of winter oilseed rape, nitrate contents in the top soil were generally elevated. There were no considerable N2O pulses observed during thawing of frozen soil. Winters were mild without any severe frost periods in all three surveyed years which could be a reason for the generally low N2O winter fluxes observed in this study. On all examined sites, increasing N fertilization significantly enhanced N2O flux rates. Data obtained during the study were used to augment an existing model, wherefrom a new emission factor for OSR can be calculated. Assuming a quantity of 200 kg N ha-1 the global fertilizer-related emission factor derived from the exponential model was 0.6 %. This factor is within the uncertainty range of the EF1 IPCC emission factor (0.3 % – 3.0 %), but about 40 % lower than the 1 % IPCC default. The nitrification inhibitor (NI) TZ+MP combined with digestate mitigated the N2O fluxes significantly across all study sites and experimental years. As already noted in the fertilizer experiment, a high spatial and temporal variability in N2O fluxes over all sites was observed. The magnitudes of the N2O fluxes also showed similar trends. Over the entire investigation, the application of the NI significantly reduced annual N2O emission by a factor of three. During the fertilization period this mitigation effect was six times significant. This clearly emphasizes the importance of annual data sets to avoid overestimating NI effects.
Profiling of physiological responses and quality aspects in Vitis vinifera L. as influenced by aspects of N application
(2019) Lang, Carina Paola; Zörb, Christian
Viticulture and the vinification of vines (Vitis vinifera L.) to wine is an important branch in agriculture world-wide. Berry quality and the associated wine quality are the driving factors here. Nitrogen (N) is the most important plant nutrient for the grapevine. In addition to its influence on vegetative and generative growth, it determines significantly the metabolite composition and the oenological parameters of the grape berry. Nitrogen is present in various forms, such as nitrate, ammonium or amino acid, in the individual plant organs and is used differently by the grapevine. Grapevines are believed to have the ability to assimilate N in various forms, which in turn may affect the quality of berries and the resulting wine. For a better understanding of the effects of N on berry and wine quality, knowledge of which N-form can be assimilated by the vine and the way that this affects oenological parameters and quality-giving metabolites is essential. To this end, several investigations were carried out at various test levels, starting with hydroponic experiments, a pot experiment and a further field experiment, and on the matured wine. The various N-forms of nitrate, ammonium, urea and the amino acids arginine and glutamine were applied, following which the plant-physiological reactions of the grapevine and quality-determining parameters in berry and wine were measured. Furthermore, a metabolite profile with a focus on phenolic components was prepared and a sensory analysis of the wine was performed. The grapevines in the hydroponics and pot experiments were treated with 4 mM total N. The grapevines in the field experiment were fertilized with 60 kg N ha-1, calculated in relation to the block size. The rootstocks SO4 and RU140 showed similar patterns of N assimilation with respect to the N-form but differed significantly with regard to the level of growth and N content among all N-forms. The N-sensitive rootstock SO4 reacted more strongly than the rootstock RU140 and, therefore, SO4 was used for further experiments. This suggests that grapevines are able to assimilate the amino acids glutamine and arginine, as also shown by the enzymatic nitrate reductase activity and the increased abundance of the transcripts of nitrate reductase and nitrite reductase. Nevertheless, the N-forms NO3- and NH4+ were preferentially assimilated. The assimilation under urea treatment was significantly reduced. In addition to the N-form, the amount of N applied had an influence on N assimilation in the grapevine. With increasing amounts, the vegetative and generative growth increased up to a threshold. However, if this threshold was exceeded, both were significantly reduced. If the grapevine is overfertilized, the sink : source ratio changes, which will lead to a change in the biomass production and furthermore to a saturation and storage of N. In addition, competition for assimilates occurs, this alters the N distribution and N availability within the plant and the berries. The N-form has no influence on berry yield. The oenological and chemical parameters of the must and the wine are of enormous importance for product quality. The key components include pH and acidity, which contribute significantly to the organoleptic properties of wine. Both factors are influenced by the N-form and the amount of N offered. As the amount of N increases, the pH increases and the acidity decreases. The N-forms NO3- and urea and, the zero application (without additional N) show the highest influences. The must weight is a defining factor reflecting the berrys maturity and thus the time of harvest. As the amount of N increases, the must weight decreases. On the one hand, an increased N amount leads to lower acidity in the berry, indicating that more sugar is being stored and that the berry is in an advanced stage of maturity. On the other hand, an increased N amount leads to a decreasing must weight, which leads further to a maturation delay. The total phenolic content increases with increasing N amount, but is highest following zero N application. Tentative phenols measured in the metabolite profile are markedly down-regulated after urea treatment and are upregulated with NO3- following NH4+ treatment. This result might arise from reduced N assimilation in the root and thus reduced N availability for the berries. The influence of N on the aroma and sensory aspects of wine is controversial. The individual aroma attributes show both an increase and a decrease in their intensity attributable to N, mainly urea and NO3-. A marked influence between N-treated vines and the zero application is also apparent. However, these contrasting results clearly show that aroma and thus the sensory characteristics of wine can be influenced both positively and negatively. The results of the aroma and sensory evaluation in the agroforestry system underline once again the controversial influence of N on the sensory features of wine; no significant influence was measured. In summary, N has a significant influence on the vegetative and generative growth of the grapevine. The influence of N can be both positive and negative and is in part directly or indirectly linked to wine quality and should therefore not be ignored.
Rahmenbedingungen für eine vereinfachte „gabenreduzierte“ N-Düngung zu Winterweizen (Triticum aestivum L.)
(2018) Makary, Thomas; Müller, Torsten
The split N-fertilization with CAN in three or four doses was considered a measure to improve the nitrogen supply of winter wheat in the past and still is considered a guarantor for good yield and quality. The split N-fertilization with CAN is also recommended to synchronize and harmonize N-demand of the plants as well as soil N-content. The aim of the current study was to analyze simplified (reduced number of N-servings) CAN strategies to winter wheat and the necessity of split nitrogen servings in order to achieve yield and quality aims. This interest was occasioned by impressive results of experiments on farmers’ fields using simplified N- strategies with CAN. Simplified CAN fertilization strategies are able to produce high grain yield and protein contents with winter wheat when the N-supply is ensured. Therefore, the common split N-servings with CAN are not necessary. Simplified strategies with UAN seem to be possible, but this requires further research on application techniques to reduce NH3 losses. Simplified CAN fertilization strategies were tested based on modern wheat varieties and the high plasticity in the development of the yield compounds. Modern wheat varieties show low harvest-indices which is important to reduce the risk of lodging. Furthermore, these varieties are able to overcome omitted N-servings through remobilization of N in the plants. Suboptimal conditions during the development within one important growing stage can be compensated during later growing stages when the growing conditions are better. These properties in combination with a late first application (BBCH 29/31) of N turned out to be the “gold standard” in our experiments. Reduction processes during the tillering (BBCH 25/27) period when N is applied confirm these findings. In addition, the application date for the heading stages (BBCH 49/51) when temperatures are high and conditions very dry have to be considered. Simplified N-fertilization systems can also be applied on Luvisols if the soils are not long-term fertilized by liquid manure. The positive soil characteristics of these soils and the high soil-borne fertility support the approach with simplified CAN strategies. In this situation, N-leaching into deeper soil layers is not likely as high precipitation rates in a short time would be necessary to cause this. In fact, a long term liquid manure application with high rates is not necessary when simplified CAN treatments are applied. Moreover, high N amounts in soils caused by long term liquid manure applications are a risk for N-losses and environmental pollution. Notwithstanding the above, organic fertilizers like liquid manure show positive effects on the soil chemistry and the physical properties of the soil. It is important to apply a system to better include the N fertilization effect of liquid manure during the vegetation period. Additionally, simplified CAN fertilization reduces the work effort on the farms. Currently, especially for livestock farms, which rely on N-fertilization, simplified CAN treatments are a good alternative to the common practice. Whereupon on shallow or sandy soils the approach with simplified CAN treatments should be restricted since these soils mostly show low water holding capacities and high percolate water rates. Under suboptimal growing conditions with high precipitation rates simplified CAN treatments can be a risk for the environment and the groundwater. Apart from that, the volatile weather conditions are the most important factor for yield and quality outcome. Mild conditions during the early winter lead to prolonged growing of the plants. In spring the number of tillers per m-2 is already determinated. Therefore, a combination of N doses at the beginning of the growing season in order to promote the number of tillers doesn´t yield the aimed results. The properties of modern wheat cultivars, tested soils, weather conditions and constraints of simplified CAN treatments show the complexity of N fertilization of winter wheat. Standard measures like the common split CAN fertilization are neither wrong nor ideal to create high yield and protein contents with a minimum of input. The most important items for a successful wheat production are high knowledge and attention levels for the plants and growing conditions. Combining the fertilizer requirement calculation and the knowledge on the field yield potential, the yield and quality of winter wheat can be optimized with a minimum of input.
Soil water status shapes nutrient cycling in agroecosystems from micrometer to landscape scales
(2022) Bauke, Sara L.; Amelung, Wulf; Bol, Roland; Brandt, Luise; Brüggemann, Nicolas; Kandeler, Ellen; Meyer, Nele; Or, Dani; Schnepf, Andrea; Schloter, Michael; Schulz, Stefanie; Siebers, Nina; von Sperber, Christian; Vereecken, Harry
Soil water status, which refers to the wetness or dryness of soils, is crucial for the productivity of agroecosystems, as it determines nutrient cycling and uptake physically via transport, biologically via the moisture‐dependent activity of soil flora, fauna, and plants, and chemically via specific hydrolyses and redox reactions. Here, we focus on the dynamics of nitrogen (N), phosphorus (P), and sulfur (S) and review how soil water is coupled to the cycling of these elements and related stoichiometric controls across different scales within agroecosystems. These scales span processes at the molecular level, where nutrients and water are consumed, to processes in the soil pore system, within a soil profile and across the landscape. We highlight that with increasing mobility of the nutrients in water, water‐based nutrient flux may alleviate or even exacerbate imbalances in nutrient supply within soils, for example, by transport of mobile nutrients towards previously depleted microsites (alleviating imbalances), or by selective loss of mobile nutrients from microsites (increasing imbalances). These imbalances can be modulated by biological activity, especially by fungal hyphae and roots, which contribute to nutrient redistribution within soils, and which are themselves dependent on specific, optimal water availability. At larger scales, such small‐scale effects converge with nutrient inputs from atmospheric (wet deposition) or nonlocal sources and with nutrient losses from the soil system towards aquifers. Hence, water acts as a major control in nutrient cycling across scales in agroecosystems and may either exacerbate or remove spatial disparities in the availability of the individual nutrients (N, P, S) required for biological activity.
Transcriptional and proteomic responses towards early nitrogen depletion in Arabidopsis thaliana
(2016) Menz, Jochen; Ludewig, Uwe
Plant roots acquire nitrogen predominantly as ammonium and nitrate, which besides serving as nutrients, also have signaling roles. Re-addition of nitrate to starved plants rapidly and di-rectly transcriptionally re-programs the metabolism and induces root architectural changes, but the earliest responses to nitrogen deprivation are unknown. In this thesis, the early transcriptional response of developed roots to nitrate or ammonium deprivation were analyzed in two Arabidopsis ecotypes contrasting in their nitrogen use efficiency: the inefficient genotype Col-0 and the efficient Tsu-0. The rapid transcriptional repression of known nitrate-induced genes proceeded the tissue NO3- concentration drop, with the transcription factor genes LBD37/38 and HRS1/HHO1 among those with earliest significant change. Some transcripts were stabilized by nitrate, but similar rapid transcriptional repression occurred in loss-of-function mutants of the nitrate response factor NLP7. In contrast, an early transcriptional response to ammonium deprivation was almost completely absent. In Col-0, the analysis was extended with the proteome and phospho-proteome resulting in a rapid and transient perturbation of the proteome induced by ammonium deprivation and a differential phosphorylation pattern in proteins involved in adjusting the pH and cation homeostasis, plasma membrane H+, NH4+, K+ and water fluxes. Fewer differential phosphorylation patterns in transporters, kinases and other proteins occurred with nitrate deprivation. The deprivation responses are not just opposite to the resupply responses, identify NO3--deprivation induced mRNA decay and signaling candidates potentially reporting the external nitrate status to the cell. Transcrip-tome comparison revealed only few N-nutrition related genes between both ecotypes contributing the increased NUE of Tsu-0, which probably relies on higher biomass accumulation. Besides, Tsu-0 confirmed the transcriptional depletion response of Col-0.
Untersuchungen zur Abundanz der Reblaus (Dactylosphaera vitifolii Shimer) und zur Nodositätenbildung in Abhängigkeit von Umweltfaktoren
(2000) Kopf, Andreas; Blaich, Rolf
The aim of the examinations was to investigate the abundance of Phylloxera (Dactylosphaera vitifolii Shimer), the occurrence of different biotypes of Phylloxera, the reaction of rootstocks to the infestation by Phylloxera and the influence of abiotic environmental conditions on the interaction between insect and plant. To investigate this interaction galls on rootlets (nodosities) and leaf galls were examined. The abundance of Phylloxera and the issue of the holocyclical reproduction in the wine region palatinate were evaluated in a field monitoring. In a special field trial the occurrence of different stages of Phylloxera and their damages on the rootstock were registered. With a dual aseptical in vitro system Phylloxera of different origins were examined on their aggressiveness to different varieties of rootstocks. In pot trials the influence of the type of soil and the effect of N-fertilization on the development of nodosities were investigated. The results of the examination show that Phylloxera can be found in nearly every part of the palatinate and that the improper cultivation of grafted rootstocks promotes the spreading of Phylloxera. Through shoots of rootstocks ? as they can be found in vineyards run wild - a holocyclical development of Phylloxera is made possible under appropriate climatical circumstances. Fitness, population dynamics of Phylloxera and the number of nodosities caused by the insects are correlating with their adaptation to a host rootstock. Pot studies have demonstrated that Phylloxera populations develop better in clay soil than sandy soil. High densities of Phylloxera in combination with a lack of N-supply increase a growth depression on grafted roots. It could also be proved that N-fertilization reduces the Phylloxera populations and the development of nodosities up to 98 %.
The wheat AMT2 (AMmonium Transporter) family, possible functions in ammonium uptake and pathogenic/symbiotic interactions
(2023) Porras‐Murillo, Romano; Zhao, Yufen; Hu, Jinling; Ijato, Toyosi; Retamal, Joseline Palafox; Ludewig, Uwe; Neuhäuser, Benjamin
Ammonium uptake into wheat roots relies primarily on two AMmonium Transporters of subfamily one, while the wheat genome comprises 4 to 6 AMT2 type transporters. Plant AMT2s generally show functions in root‐to‐shoot translocation or pathogenic and symbiotic plant–microorganism interactions. We addressed the activity of TaAMT2s in ammonium transport. Nitrogen‐dependent expression implicated a physiological function in ammonium uptake for TaAMT2;1 and in ammonium distribution for TaAMT2;2‐6.