Browsing by Subject "Nitrification"

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Leaf gas exchange of lowland rice in response to nitrogen source and vapor pressure deficit
(2021) Vu, Duy Hoang; Stürz, Sabine; Pieters, Alejandro; Asch, Folkard
Background: In anaerobic lowland fields, ammonium (NH4+) is the dominant form of nitrogen (N) taken up by rice plants, however, with the large expansion of water-saving irrigation practices, nitrification is favored during drained periods, leading to an increased availability of nitrate (NO3−). Aim: Since the uptake and assimilation of the two N-sources differ in their demand of pho- tosynthates, leaf gas exchange may be subject to adjustments in response to N-sources, particularly at high evaporative demand, when stomatal conductance (gs) is very sensitive. Methods: Three experiments were carried out to study leaf gas exchange of various low- land rice varieties in response to N-source at low and high vapor pressure deficit (VPD). In the first experiment, seedlings of 12 rice varieties were grown at high VPD for 3 weeks. From this, four rice varieties differing in gs and CO2 assimilation rate (A) were selected and grown for 2 weeks at low VPD, and after that, they were shifted to high VPD for 1 week, whereas in the third experiment, the same varieties were grown separately at low and high VPD conditions for 2 weeks. In all three experiments, plants were grown hydroponically in nutrient solution with N-sources as sole NH4+ or NO3−. Results: At high VPD, NO3− nutrition led to a higher gs and A in four out of 12 varieties (IR64, BT7, NU838, and Nipponbare) relative to NH4+ nutrition, while no effect was observed at low VPD or after a short-term exposure to high VPD. Further, varieties with a high intrinsic water-use efficiency (WUEi; IR64 and BT7) showed the strongest response to N-source. Higher gs was partially supported by increased root/shoot ratio, but could not be fully explained by the measured parameters. However, higher A in NO3−-fed plants did not always result in increased plant dry matter, which is probably related to the higher energy demand for NO3− assimilation. Our results suggest that at high VPD, NO3− nutrition can improve leaf gas exchange in varieties having a high WUEi, provided a sufficient water supply. Conclusion: Therefore, intensified nitrification under water-saving irrigation measures may improve leaf gas exchange and the growth of rice plants under high transpirational demand. However, choice of variety seems crucial since large varietal differences were observed in response to N-source. Further, breeding strategies for genotypes adapted to aerobic soil conditions should consider responses to NO3−, potentially using gas exchange measurements as a screening tool.
Metabolome fingerprinting reveals the presence of multiple nitrification inhibitors in biomass and root exudates of Thinopyrum intermedium
(2024) Issifu, Sulemana; Acharya, Prashamsha; Schöne, Jochen; Kaur-Bhambra, Jasmeet; Gubry-Rangin, Cecile; Rasche, Frank
Biological Nitrification Inhibition (BNI) encompasses primarily NH4 +-induced release of secondary metabolites to impede the rhizospheric nitrifying microbes from per- forming nitrification. The intermediate wheatgrass Thinopyrum intermedium (Kernza®) is known for exuding several nitrification inhibition traits, but its BNI potential has not yet been identified. We hypothesized Kernza® to evince BNI potential through the presence and release of multiple BNI metabolites. The presence of BNI metabolites in the biomass of Kernza® and annual winter wheat (Triticum aestivum) and in the root exudates of hydroponically grown Kernza®, were fingerprinted using HPLC-DAD and GC–MS/MS analyses. Growth bioassays involving ammonia-oxidizing bacteria (AOB) and archaea (AOA) strains were conducted to assess the influence of the crude root metabolome of Kernza® and selected metabolites on nitrification. In most instances, significant concentrations of various metabolites with BNI potential were observed in the leaf and root biomass of Kernza® compared to annual winter wheat. Furthermore, NH4 + nutrition triggered the exudation of various phenolic BNI metabolites. Crude root exudates of Kernza® inhibited multiple AOB strains and completely inhibited N. viennensis. Vanillic acid, caffeic acid, vanillin, and phenylalanine suppressed the growth of all AOB and AOA strains tested, and reduced soil nitrification, while syringic acid and 2,6-dihydroxybenzoic acid were ineffective. We demonstrated the considerable role of the Kernza® metabolome in suppressing nitrification through active exudation of multiple nitrification inhibitors.
Unveiling the plant-associated microbiome responses and nitrification inhibition aspects of perennial intermediate wheatgrass (Thinopyrum intermedium)
(2025) Issifu, Sulemana; Rasche, Frank
Perennialization of agriculture has recently garnered attention as a nature-based solution (NBS) to complement predominantly annual cropping systems, offering a pathway toward sustainable agriculture and enhanced protection of agroecosystems. In this regard, the perennial intermediate wheatgrass, Thinopyrum intermedium, trade name Kernza®, has been proposed as a model plant for achieving perennialization of cereal cropping systems. Kernza® provides a broad range of ecosystem services, including enhanced carbon sequestration, enhanced biodiversity, and regulation of the nitrogen (N) cycle. Some studies reported regulated nitrification in Kernza® fields through reduced N2O emissions, low N leaching, and high legacy N. These traits indicate a plant-exerted control of nitrification through the secretion of bioactive metabolites, a concept known as biological nitrification inhibition (BNI). However, no study had investigated the mechanism behind these BNI traits of Kernza®. Relatedly, existing BNI studies have largely been confined to the identification and testing of single and novel metabolites. Moreover, while some studies have reported the ability of Kernza® to stimulate microbial activity and enhance microbial diversity, there is currently no study in a European context on the potential influence of Kernza® on the rhizosphere microbiome. Thus, this doctoral study aimed to fill these knowledge gaps. The first study used a metabolome fingerprinting approach to profile the metabolome of the Kernza® biomass collected from the field and root exudates collected under N sources (ammonium (NH4+) versus nitrate (NO3-)) in a hydroponic system. Multiple nitrification inhibitors, including several phenolic metabolites, were identified in higher quantities in the biomass of Kernza® than in annual wheat. These metabolites were also concurrently exuded in higher quantities by the roots of Kernza® under NH4+-N source than NO3--N source. Bioassays involving multiple ammonia-oxidising bacteria and archaea (AOB and AOA) confirmed the antimicrobial properties of crude root exudates of Kernza®, as well as individual metabolites such as caffeic acid, vanillic acid, vanillin, and phenylalanine. Soil incubation experiments further demonstrated the nitrification inhibition potential of all tested metabolites, except phenylalanine. This study presents the initial evidence elucidating the mechanisms by which Kernza® regulates nitrification and clarifies the function of Kernza’s® metabolome in mediating nitrification inhibition. In the second study, a pairwise combinatorial approach was employed to assess the interactions among biochemically distinct metabolites co-exuded by Kernza® – caffeic acid, vanillic acid, vanillin, and phenylalanine – against multiple ammonia-oxidisers and soil nitrification. It was found that the metabolites interacted both synergistically and antagonistically against the test strains and soil nitrification, with antagonism being the most predominant interaction among the metabolites. Caffeic acid exhibited single agent dominance (SAD), dominating all other metabolites in all combinations. Furthermore, nitrifiers responded differentially to the metabolites – affirming that nitrifiers are differentially sensitive to inhibitors. Both individual and paired metabolites inhibited the growth of multiple AOB and AOA, as well as soil nitrification – suggesting that both synergism and antagonism did not impair the inhibitory potentials of the metabolites. This evidence suggests that biochemically distinct metabolites exuded by Kernza® and other BNI-positive plants may be interacting in diverse ways in the rhizosphere to suppress nitrification. The third study assessed the impact of Kernza®-induced perennialization on rhizomicrobiome and root endophytes in comparison to annual wheat under an agroclimatic gradient (Sweden, France, and Belgium). The results suggest pronounced similarities in the rhizobacterial composition of Kernza® and annual wheat, with no significant difference in the alpha diversity of their rhizomicrobiome. Beta diversity analysis revealed that factors such as country (agroclimatic conditions), sampling depth (spatial), and year (temporal) rather exerted greater influence than crop type. Notwithstanding, Kernza® promoted the stability of the rhizomicrobiome than annual wheat based on year-on-year comparison – suggesting that perennialization has the ability to protect rhizomicrobiome from ecological perturbation. Moreover, Kernza® recruited and internalised a higher proportion of the rhizosphere microbiome into its root tissues compared to annual wheat, indicating a potential role of crop-associated microbiomes in the lifecycle of Kernza®. Furthermore, an environment-wide comparison with agroecologically relevant database revealed that Kernza®, compared to annual wheat, harboured a significant proportion of rhizobacterial taxa associated with the rhizosphere and grassland ecosystems – supporting the notion that Kernza® shares ecological characteristics with natural grasslands. This study adds to the growing body of knowledge on the rhizosphere ecology of Kernza® and provides further evidence for the ecosystem service potential of Kernza®.
Ein Vergleich zwischen Barometrischer Prozessseparation (BaPS) und 15N-Verdünnungsmethode zur Bestimmung der Bruttonitrifikationsrate im Boden
(2010) Schwarz, Ulrich; Streck, Thilo
Besides the carbon cycle, the nitrogen cycle plays a central role in soil. A key process of this cycle is nitrification. In practice, nitrification is measured as gross or net nitrification. Net nitrification rates are measured by determining the net change in the nitrate or ammonium pool over a period of time. Net rates are difficult to interpret, because the net nitrification rate is the sum of nitrate producing and consuming processes. In contrast, gross nitrification quantifies the total production of nitrate via nitrification. There are two methods for measuring gross nitrification: the 15N-Pool dilution technique and Barometric Process Separation (BaPS). In the 15N-Pool dilution technique, nitrate en-riched with the heavier isotope 15N is added to soil, and the dilution of the 15N pool and the change in the nitrate pool are measured over time. The BaPS method measures changes in pressure and the oxygen- and carbon dioxide concentration of the atmosphere in a closed chamber. The gross nitrification rate can then be computed by a step-by-step solution of the gas balance equations. In the present study, 15N enriched nitrate was added to soil and then put into the BaPS-incubation chamber. By this procedure gross nitrification rates were measured simultaneously with both the 15N-Pool dilution technique and the BaPS method. The aim of the present study was to find out under which conditions the two methods yield similar results and under which conditions different results. In the latter case, the thesis aimed at elucidating the cause for the disagreement between both methods. For this purpose extensive research on two agricultural soils from North China and three soils from Southwest Germany was undertaken. The two methods were compared under the following conditions: 1) application of ammonium fertilizer, 2) addition of nitrification inhibitors, 3) varying soil wa-ter contents, and 4) different soil temperatures. Moreover, a new methodological approach was tested: the 13CO2-Pool dilution technique. Combining this method with the 15N-Pool dilu-tion technique and the Barometric Process Separation made it possible to exactly determine the pH and respiration coefficient in situ. Both techniques corresponded well in soil with pH<6. In soil with higher pH, both methods led to very different results. The reason is that pH has a strong impact on the calculation of the nitrification rate in the BaPS method. In nearly all experiments with neutral to alkaline soils, the BaPS technique yielded higher nitrification rates than the 15N-Pool dilution technique if pH was determined in 0.01 M CaCl2. With pH determined in water, there was good agreement or nitrification rates were too low. Fertilization with ammonium did not in-duce an increase of nitrification in a sandy soil with pH<6. A decrease in nitrification to less than 60% was achieved by the application of the nitrification inhibitor DCD. For both techniques a positive correlation between temperature and nitrification rates was found. There was no correlation between water filled pore space and nitrification rate.