Browsing by Subject "Nitrification"
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Publication Leaf gas exchange of lowland rice in response to nitrogen source and vapor pressure deficit(2021) Vu, Duy Hoang; Stürz, Sabine; Pieters, Alejandro; Asch, FolkardBackground: 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 hydroponi- cally 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 vari- eties (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− nutri- tion 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.Publication 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, FrankBiological 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.Publication Ein Vergleich zwischen Barometrischer Prozessseparation (BaPS) und 15N-Verdünnungsmethode zur Bestimmung der Bruttonitrifikationsrate im Boden(2010) Schwarz, Ulrich; Streck, ThiloBesides 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.