秸秆还田条件下蚯蚓-菌根互作对麦田N2O排放的驱动机理

Agroecosystem represents the largest global source of anthropogenic N2O emissions. To date, studies are active but still controversial for N2O emission from agricultural soils. However, it is necessary to elucidate the effects and mechanisms of N2O emissions from residue-amended soils. As two important components for N-cycling in agroecosystems, the regulative roles of earthworm and mycorrhizae interactions have long been overlooked for N2O emissions from straw incorporated soils. This project will target at the 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 to earthworm additions in the wheat fields under different straw incorporation methods; (2) Effects of earthworm-mycorrhiza interactions on nitrification, denitrification and their relative contribution to N2O emissions in the straw amended soils; and (3) Effects of earthworm-mycorrhiza interactions on the mineralization of 15N in rice straws and the uptake of 15N by wheat plants; and (4) Effects of earthworm-mycorrhiza interactions on microbial transformation of ammonium and nitrate. This study will disentangle the soil biota-regulated pathway of N2O emissions from straw-incorporated soils and increase knowledge about the ecological functioning of soil biodiversity in agroecosystems. This study also has implications for N2O mitigation in agricultural production.

农田系统是氧化亚氮(N2O)最主要的排放源。目前，国内外关于农田土壤N2O排放的研究与争论十分活跃。然而，秸秆还田对N2O排放的影响及机制有待阐明。作为农田土壤N素循环的重要参与者，蚯蚓与菌根的功能互作对秸秆还田土壤N2O排放的调控作用及机制并未引起足够重视。本项目拟以稻茬麦田为研究对象，结合田间试验和温室受控试验，使用高通量测序和稳定性同位素示踪技术，研究：(1)蚯蚓对稻茬麦田秸秆还田土壤AM真菌群落的影响；(2)蚯蚓-菌根互作对稻茬麦田秸秆还田土壤硝化-反硝化过程的影响及二者对N2O排放的相对贡献；(3)蚯蚓-菌根互作对稻秸15N矿化与小麦15N素吸收的影响；(4)蚯蚓-菌根互作对稻茬麦田秸秆还田土壤矿质氮素生物转化过程的影响。研究结果将揭示秸秆还田土壤N2O排放的土壤生物调控机制，丰富土壤生物多样性在农田系统中的生态功能，为农业生产实现N2O减排目标提供理论依据。

AMF对N2O的排放和作物氮同化受秸秆还田和土壤类型的影响。在秸秆还田条件下，AMF抑制了砂土条件下N2O的排放，但不影响粘土砂土条件下N2O的排放。在砂土条件下，AMF促进了作物氮的吸收和向籽粒的转移，提高了籽粒生物量;而在粘土条件，AMF虽然提高了作物氮的吸收，但抑制了氮向籽粒的转移。蚯蚓对AMF群落结构和功能的影响依赖于秸秆还田方式；秸秆管理及其与蚯蚓互作通过改变AMF的优势种影响菌根介导的植物氮吸收。秸秆还田条件下，蚯蚓-菌根互作显著促进作物氮吸收；蚯蚓-菌根互作对N2O的排放依赖于作物生育期；在拔节期显著降低N2O的排放，而在孕穗期显著提高N2O的排放。 AMF对土壤氮转化和植物氮吸收依赖于秸秆还田方式；不同秸秆还田深度导致蚯蚓活动的变化进而影响菌根介导的氮转化。在不同还田方式下，蚯蚓-菌根均显著促进作物对秸秆源15N的吸收，但是在模拟旋耕还田条件下的效应大于模拟沟埋还田。