旱地红壤N2O排放的真菌反硝化作用和微生物介导机制

N2O emissions from agricultural soils are important parts of global N2O emissions. Because bacterial nitrification and denitrification process are well known, the emission of N2O from agricultural soils has been studied mainly by focusing on these contributions. However, some recent studies have demonstrated that fungal contributions to N2O emissions in terrestrial environments are larger than the contributions of bacterial denitrification and/or nitrification. Fungi contributed more to soil N2O production under sub-anoxic and acidic conditions and following the addition of complex substrates. Thus, fungi might play a vital role in N2O production from upland red soils, which pH is relatively low, especially when accompanied with complex substrates amendment. In this study, we will conduct incubation experiments to determine the N2O emissions in upland red soils. 15N tracing experiment will be conducted to determine soil nitrogen transformation rates and the contribution of different nitrogen transformation processes to N2O production. Site preference (SP) and substrate-induced respiration inhibition experiment will be applied to study the contribution of fungal denitrification to soil N2O production. Real-time quantitative PCR, amplicon sequencing and metagenomic sequencing will be used to determine the copy number of functional genes and microbial community structure and then verify the underlying microbiological mechanisms of fungal denitrification. The key fungi which conduct fungal denitrification will be isolated and determine their N2O production activities. These results contribute data and knowledge on the understanding of fugal denitrification and N2O mitigation in upland red soils.

农田土壤是重要的N2O人为排放源，长期以来细菌被认为是农田土壤N2O排放的主要驱动者，但新近发现真菌也可能起着重要作用，可以在好氧、强酸性和含有复杂有机物质的土壤中反硝化产生N2O。那么旱地红壤尤其是有机肥长期施用红壤是否是真菌反硝化发生的热点区域。本项目以有机无机肥长期定位试验红壤为研究对象，拟通过室内培养试验，利用15N同位素示踪技术，研究红壤氮素初级转化速率，明确不同氮素转化过程对N2O产生的贡献；采用N2O SP值和抑制剂方法，研究真菌反硝化过程及其对水分和外源碳的响应，明确真菌反硝化作用对N2O排放的贡献和关键影响因素；利用定量PCR、扩增子测序和宏基因组技术，研究氮素转化功能基因丰度和群落结构，解析N2O产生的关键微生物；利用分离纯培养技术，甄别驱动真菌反硝化的关键物种，测定其N2O产生能力，阐明旱地红壤真菌反硝化过程的微生物介导机制，为旱地红壤N2O减排措施提出提供科学依据。

农田土壤是氧化亚氮（N2O）的重要排放源，长期以来细菌被认为是农田土壤N2O排放的主要驱动者。然而，真菌也可以产生N2O，但真菌在农田红壤N2O排放中的相对贡献尚不清楚。本项目通过采集中国科学院鹰潭红壤生态实验站不同施肥模式的长期试验地土壤，建立室内培养试验，定期监测N2O排放通量，在N2O排放高峰期采集土壤测定氮循坏微生物功能基因丰度，解析真菌反硝化功能基因fungal nirK在N2O排放中的作用；进行团聚体分级，研究真菌反硝化功能基因在团聚体中的分布特征；利用研究团队先前建立的田间原位试验定期采集的土壤，测定氮循环功能基因丰度，阐明真菌反硝化在旱地农田红壤N2O排放中的作用。取得如下成果：（1）结合室内培养试验和田间原位试验，明确了真菌反硝化功能基因fungal nirK是解释土壤N2O排放通量的重要因子，表明真菌反硝化在旱地农田红壤N2O排放过程中发挥重要作用；（2）阐明了添加秸秆显著提高旱地农田红壤真菌反硝化功能基因fungal nirK丰度，真菌反硝化在施用秸秆的农田红壤中对N2O排放的相对贡献可以达到96%；（3）揭示了fungal nirK基因丰度不仅受施肥影响，还受团聚体影响，fungal nirK基因在微团聚体和粉砂黏粒中的丰度比大团聚体和小团聚体高，表明了微团聚体可能更有利于真菌反硝化的发生。本项目深化了我们对旱地农田红壤真菌反硝化过程的认识，并可为旱地农田红壤养分管理和温室气体减排措施制定提供理论依据和实践指导。