紫云英还田条件下稻田N2O排放的微生物学机制研究

Paddy fields are important emission sources of N2O, which has been titled as a great radioactively active greenhouse gas. The study of key technologies in reducing N2O emission from paddy fields and their mechanisms are of important significance in the construction of greenhouse gas mitigation rice cropping systems. The application of nitrogen fertilizer is a main factor causing N2O emission. The incorporation of Chinese milk vetch, a familiar leguminous green manure, could replace or partly replace nitrogen fertilizer to provide nitrogen nutrition for rice growth. However, little studies have systemically evaluated its effects on N2O emission from paddy fields and the action mechanisms. Based on a 7-year continuous field experiment with three treatments (milk vetch, half milk vetch and half urine, and urine), this program will monitor N2O emission flux; measure soil physical and chemical properties and analysis the richness and community structures of three most important genes associated with N2O emission including nirK gene, nosZ gene and amoA gene by using fluorescence quantitative PCR and T-RFLP, respectively. The aim of the program is to evaluate the effects of milk vetch incorporation on N2O emission from paddy fields and clarify its action mechanisms from the perspective of soil physical and chemical properties and molecular ecology. The results of this program will improve the paddy soil nitrogen cycling theories associated with N2O emission and provide theoretical guidance and technical support for the foundation of greenhouse gas mitigation rice cropping systems.

稻田是强效应温室气体N2O的重要排放源，研究能够减缓稻田N2O排放的关键技术及其过程机理对构建温室气体减排的稻作制度具有重要意义。施用氮肥是导致稻田N2O排放的最主要原因，豆科绿肥紫云英可替代或部分替代氮肥为水稻提供氮素营养，但紫云英还田对稻田N2O排放的影响及作用机制尚缺乏系统深入研究。本申请项目以连续7年田间定位试验（设紫云英替代全部氮肥、紫云英替代半量氮肥、单施尿素三个处理）为基础，通过监测田间N2O排放通量和土壤理化性状，使用荧光定量PCR和T-RFLP技术分别分析N2O释放密切相关的nirK基因、nosZ基因和amoA基因的丰富度和微生物群落结构组成，明确紫云英还田对稻田N2O排放规律的影响，从土壤理化性状和分子生态学角度阐明紫云英还田对稻田N2O排放的作用机制。研究结果将有利于完善稻田N2O排放相关的氮素循环理论，为构建温室气体减排的稻作制度提供理论指导与技术支撑。

本研究在长达7年的田间定位试验上开展了紫云英还田全量和半量替代化学氮肥对稻田N2O 排放动态规律的影响极其与土壤理化性状的关系，采用荧光定量PCR和高通量测序法研究了紫云英还田对稻田土壤N2O排放相关微生物（nirK 基因、nosZ 基因和amoA 基因）群落结构和数量的影响，深入探讨了紫云英还田对稻田土壤N2O排放的微生物驱动机制。研究结果表明：（1）双季稻区紫云英替代化学氮肥具有较大的N2O 减排潜力。施用尿素在早稻和晚稻晒田后出现明显N2O 排放峰，但紫云英替代和半量替代化学氮肥后没有出现明显N2O 排放峰。说明紫云英替代化学氮肥具有一定的N2O 减排潜力。（2）稻田土壤N2O排放与土壤铵态氮呈极显著正相关，与土壤温度、土壤pH、Eh、土壤硝态氮等相关性不显著。（3）紫云英还田降低了早稻稻田土壤氨氧化古菌（AOA）和氨氧化细菌（AOB）数量，土壤总碳是影响稻田土壤AOA群落结构的主效环境因子，土壤铵态氮是影响稻田土壤AOB群落结构的主效环境因子。（4）与施用尿素相比，紫云英还田显著降低了早稻分蘖期nosZ基因丰度，但增加了晚稻分蘖期nosZ基因丰度。紫云英还田改变了早稻nosZ基因细菌的多样性指数，紫云英还田或施氮不会改变稻田土壤的反硝化nirK基因细菌的群落多样性及丰富度。土壤总氮和土壤碳氮比分别是影响nirK基因与nosZ基因型反硝化微生物群落结构的主效因子。上述研究结果证实了紫云英还田替代或部分替代化学氮肥具有减少N2O 排放潜力，探明了影响稻田 土壤N2O排放的相关微生物作用机制。