秸秆还田土壤丛枝菌根真菌对氧化亚氮排放的调控机制

Agroecosystem represents the largest global source of anthropogenic N2O emissions. To date, studies are active but controversial about N2O emission from agricultural soils. As one agricultural practice advocated by government, crop residue addition has great impacts on N2O emissions. However, its potential mechanism needs further investigation. Although it is a consensus that arbuscular mycorrhizal fungi (AMF) are important participants in soil nitrogen cycling, their regulative roles in crop residue mediated N2O emissions have long been overlooked. This project will target at wheat fields of a rice-wheat rotation system. Field and greenhouse experiments will be conducted by combining high-throughput sequencing and isotope tracer techniques. This project will investigate (1) responses of AMF community in wheat fields to different rice straw returning methods (straw incorporation with rotary tillage and concentrated-ditch-buried straw return); (2) effects of reduced AMF abundance on denitrification of rice straw incorporated soils; and (3) AMF-mediated mechanisms of N2O emissions from rice straw incorporated soils. This study will disentangle the mycorrhizae-regulated pathway of N2O emissions from straw incorporated soils and increase knowledge about AMF ecological functioning in agroecosystems. This study also has implications for N2O mitigations in agricultural productions.

农田生态系统是氧化亚氮 (N2O) 最大的排放源，国内外关于农田土壤N2O排放的研究与争论十分活跃。作为政府倡导推行的农作措施之一，秸秆还田对农田土壤N2O排放具有重要影响，然而，其具体调控机制有待进一步揭示。作为土壤氮素循环的重要参与者之一，丛枝菌根真菌对秸秆还田土壤N2O排放的调节作用并未引起足够重视。本项目拟以稻麦两熟制麦田为研究系统，通过设计田间试验和温室控制试验，结合高通量测序手段和稳定性同位素示踪技术，研究 (1) 麦田土壤丛枝菌根真菌群落对不同稻秸还田方式（常规粉碎旋耕和新型集中沟埋还田）的响应规律；(2) 丛枝菌根真菌多度降低（苯菌灵+尼龙网分隔）对稻秸还田麦季土壤反硝化过程的影响；(3) 丛枝菌根真菌对稻秸还田土壤N2O排放的调控机制。研究结果将揭示秸秆还田土壤N2O排放的菌根调控机制，丰富丛枝菌根真菌在农业系统中的生态功能，为农业生产实现N2O减排目标提供理论依据。

稻茬麦田AMF群落结构显著受到秸秆还田深度、还田量和还田方式的影响。其中，AMF群落物种组成对秸秆还田处理的响应较为敏感。秸秆还田深度对AMF群落组成的影响主要是通过调控SOC和TN浓度，进而影响C/N而进行。秸秆还田量是通过分别影响WC、TN和AK来调控AMF群落组成。秸秆还田方式对AMF群落组成的影响通过WC来影响SOC，进而影响C/N而进行。无论是秸秆还田深度和还田量，还是还田方式，均显著降低AMF群落多样性，其中，粉碎旋耕还田对AMF多样性的抑制效应最大。秸秆沟埋深度可以调控AMF群落构建过程由生态位过程向中性过程转化，但沟埋量和还田方式并未表现出如此现象。. AMF能调控小麦生物量在根冠之间的分配，但依赖于秸秆还田方式和剩余时期。AMF介导的根冠整合能够影响植株的氮素吸收和土壤有效氮素含量。AMF能够抑制土壤反硝化酶活性，但是，AMF对N2O排放通量的影响并未表现出一致的抑制现象。AMF是N2O排放的一个重要调控因子，但是，其调控效应依赖于小麦生育期和秸秆还田方式。经过全生育期监测，AMF能够极大促进CK条件下N2O的吸收与消耗，但促进了秸秆还田条件下的N2O排放。. 在模拟秸秆粉碎旋耕还田条件下，AMF促进了NH4+-N向NO3--N转化，却降低了植株对N素的吸收，增加了反硝化酶活性，从而驱动N2O排放。在模拟秸秆集中沟埋还田条件下，AMF对N素循环的调控依赖于土壤类型。在粘土条件下，AMF促进NH4+-N向NO3--N转化，但并未影响植株的N吸收，导致NO3--N在土壤积累，提供丰富的反硝化作用底物，从而促进N2O排放。然而，在砂土条件下，AMF显著促进植株的N素吸收，同时驱动NO3--N向NH4+-N转化，降低了反硝化酶活性，从而降低N2O排放。