Nitrification as function of nutrient limitation and stoichiometry

全球农业氮肥正在稳步增加，为植物提供氮素，但也向土壤微生物提供氮素，如亚硝酸单胞菌和亚硝酸盐氧化菌，这些微生物对硝酸盐(NO3-)和氧化亚氮(N2O)的产生产生重要影响，这些都是水圈和大气的潜在污染物。异养微生物和硝化微生物都有特定的化学计量比C：N：P要求。大多数硝化菌是自养的，能够根据二氧化碳和矿质氮(NH3)的氧化获得能量，从而进行生化活动和生长。在有机碳受限和氮磷有效性增加的条件下，硝化作用产生的N3-和N2O可能会增加。该项目的目的是评估有机碳限制和N：P化学计量比是否确实是硝化作用的重要调节因素。实验将在高度受控的实验室条件下进行。在活性有机C的逐步分解过程中，将测量NO3-、N2O、C：N：P的化学计量比、微生物营养限制和自养硝化菌丰度。预计C：N：P的化学计量比对N的动态变化有显著的影响，从而对农业氮素的利用效率产生重大影响，特别是在碳有效性有限的分解阶段。

Global agricultural N fertilization is steadily increasing, providing N to plants, but also to soil microorganisms such as ammonia oxidizers and nitrite oxidizers, e.g. Nitrosomonas and Nitrobacter, which exert an essential influence on the production of nitrate (NO3-) and nitrous oxide (N2O) as potential pollutants of the hydrosphere and atmosphere. Both heterotrophic and nitrifying microorganisms have specific stoichiometric C:N:P requirements. Most nitrifiers are autotrophic and able to gain energy for their biochemical activity and growth based on CO2 and the oxidation of mineral N (NH3). Under organic C-limited conditions and increased N and P availability, production of NO3- and N2O due to nitrification might be increased. Aim of this project is to evaluate if organic C limitation and N:P stoichiometry indeed are important regulators of nitrification. Experiments will be performed under highly controlled laboratory conditions. NO3-, N2O, C:N:P stoichiometry, microbial nutrient limitation, and autotrophic nitrifier abundance will be measured during progressive decomposition of labile organic C. It is expected that C:N:P stoichiometry has significant influence on N dynamics and consequently on agricultural nitrogen use efficiency, particularly during transition to the decomposition phase with limited C availability.