稻田土壤硝酸根还原过程动态特征及影响因素研究

Nitrate reduction process consists of denitrification, anaerobic ammonium oxidation (Anammox) and dissimilatory nitrate reduction to ammonium (DNRA), accounting for 50% of the N fate in the rice field ecosystem. Due to methodological difficulties, precisely quantifying N loss and gain caused by nitrate reduction process is still not achieved. Previous studies related to nitrate reduction process are mainly focusing on one or two independent processes (e.g., denitrification and Anammox), whereas simultaneously investigating the occurrence rate and relative contribution of denitrification, Anammox and DNRA in the same system is lacking. The interactions and relationships among denitrification, Anammox and DNRA in the same system are also obscure. In the present project, the occurrence rate, interactions, key influencing factors and microbial mechanisms of denitrification, Anammox and DNRA in the same system will be studied in typical paddy soils using Membrane inlet mass spectrometer (MIMS) method in combination with 15N tracer technique. Results of this investigation are not only helpful to improve our understanding of N loss processes in rice field ecosystem and to reliably evaluate the environmental effects of the nitrate reduction process, but also have crucial implications for exploring potential regulating strategies.

反硝化、厌氧氨氧化（Anammox）和硝酸根异化还原成铵（DNRA）三个过程主导的硝酸根还原途径是稻田土壤氮素转化的核心途径之一，决定了稻田生态系统约50%的氮肥去向。然而，由于方法的限制，对这些过程造成的氮损失和盈余还无法准确的定量，同时，以往研究多只针对硝酸根还原的某一或某两个过程独立开展，同一体系中反硝化、Anammox和DNRA的速率、各自贡献及相互关系尚不清楚。本申请拟采用基于膜进样质谱法（MIMS）的15N同位素示踪手段，在同一体系下，同时量化稻田土壤反硝化、Anammox和DNRA的发生强度，研究其相互关系、关键影响因素和作用机理，并结合大田实验，研究水稻不同生育期稻田土壤硝酸根的消耗过程与水稻氮素需求的动态匹配关系。研究结果对于深化理解基于硝酸根还原途径的稻田土壤氮素转化过程、更加可靠的评价稻田生态系统硝酸根还原过程的环境效应以及寻找潜在氮素调控措施具有重要的理论指导意义。

本项目首选建立和完善了基于膜进样质谱法(MIMS)的稻田土壤硝酸根还原过程测定方法体系，可以获取近似原位情况下的脱氮速率，并能在同一体系中量化反硝化、Anammox和DNRA的速率和各自贡献；利用上述方法体系，系统研究了我国典型水稻土中硝酸根各还原过程的速率、各自贡献和影响因素，并比较了室内泥浆15N加标法和土柱近似原位培养法的差异；进一步结合大田实验，明确了水稻生育期硝酸根还原过程主导途径的损失动态和调控措施。研究结果表明，反硝化是稻田土壤硝酸根还原过程的主导途径，对硝酸根还原过程的贡献达76.75%−92.47%，而Anammox和DNRA同样不可忽视（占比分别为4.48−9.23%和0.54−17.63%），土壤NO3−浓度、SOC含量和nosZ丰度是影响反硝化和Anammox的主要因素，而土壤碳氮比、DOC/NO3−和硫酸根含量是DNRA过程的关键影响因素，室内泥浆15N加标法可以一定程度上反应原位情况下稻田土壤的脱氮速率，但会显著低估原位情况下的净脱氮速率。两年的田间观测显示，整个水稻生育期土壤脱氮速率介于0.10−0.91 kg N ha-1 d-1，脱氮速率峰值出现在施肥后的1-2天内，生物质炭施用显著提高水稻生育期的土壤脱氮速率（3.3%−9.7%），而硝化抑制剂施用显著降低土壤脱氮速率（9.7%−19.4%），从降低氮素损失和提高氮肥利用率角度，硝化抑制剂施用更值得推荐的调控措施。本项目共发表SCI论文6篇，项目成员入选中科院创新促进会，培养研究生3名，组织召开了两届“氮素生物地球化学循环：过程、方法与展望”青年学术论坛，向同行介绍了本项目的成果。