覆盖作物对稻田氮素利用和温室气体排放的影响及其微生物生态学机制研究

Paddy ecosystems which are usually characterized with high nitrogen input, are important emissions sources both for CH4 and N2O emissions. Studies oriented to improve technologies and their principles to enhance nitrogen use efficiency and mitigate greenhouse gases emissions are of great importance. In our previous studies, Chinese milk vetch, a winter cover crop has been found to be effective in promoting nitrogen absorption by rice plants and decreasing N2O emission, whereas it had the potential to increase CH4 emission from paddy soils. Thus, this program will study the relationship between the amount of milk vetch incorporation and nitrogen use efficiency, CH4 and N2O emissions by a combination of field experimental and 15N isotope labeling pot estimation. The most suggested amount of milk vetch incorporation will be calculated to increase nitrogen use efficiency and decrease greenhouse gases emissions. The effect of Azolla, a summer cover crop on CH4 and N2O emissions will be estimated to find ways to decrease greenhouse gases emissions to the least level. Real-time PCR and high through sequencing technologies will be introduced to analysis changes of richness and microbial community structure of 16S rRNA, pmoA, nirK, nosZ and amoA genes which are highly related to CH4 and N2O emissions to reveal the principles of milk vetch and azolla effects on greenhouse gases emissions. The results of this program will provide theoretical guidance and technical support for the foundation of nitrogen high use efficiency and greenhouse gases mitigation rice cropping systems.

稻田生态系统不仅氮素投入量大，还是CH4和N2O的重要排放源，研究既提高稻田氮素利用效率又能降低温室气体排放的关键技术具有重要意义。我们发现冬季覆盖作物紫云英可以促进水稻氮素吸收并降低稻田N2O排放，但是增加了CH4排放。因此，本申请项目拟通过大田试验和15N同位素标记盆栽相结合监测紫云英还田量与稻田氮素利用效率、CH4和N2O排放之间的关系，确定氮高效利用而且温室气体减排的最佳紫云英还田量；以此为基础，评价夏季覆盖作物红萍对紫云英还田后稻田温室气体排放的影响，利用红萍进一步减少温室气体排放；采用定量PCR和高通量测序技术分析与CH4排放相关的产甲烷古菌16S rRNA和pmoA基因，与N2O排放相关的nirK、nosZ和amoA基因丰富度和微生物群落结构变化，揭示紫云英和红萍对稻田CH4和N2O排放的微生物学机制。旨在为构建氮素高效利用而且温室气体减排的稻作制度提供理论依据和技术支撑。

水稻是我国重要的粮食作物之一，稻田是大气中温室气体CH4和N2O的农重要排放源之一，探究如何利用绿肥促进稻田碳氮循环并实现固碳减排具有重要现实意义。在不同绿肥还田量（25%紫云英-N + 75%化学N、50%紫云英-N + 50%化学 N、75%紫云英-N +25%化学N、100%紫云英-N和100%化学N）对稻田土壤碳氮循环和温室气体排放影响的田间定位试验。以此为基础课题组采用静态箱-气象色谱法研究了紫云英还田替代化学氮肥、水稻季覆盖红萍等对稻田CH4和N2O排放规律的影响；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CH4和N2O排放相关微生物（对甲烷古菌 16S rRNA、pmoA、nirK、nosZ 和 amoA 基因微生物群落结构）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CH4和N2O排放的微生物驱动机制。.研究结果表明：.（1）紫云英替代25%化学氮肥具有最大的减排潜力，与常规试用化肥处理相比CH4和N2O排放的全球增温潜势降低了12.%，单位水稻产量的全球增温潜势降低了10.3%。这一研究结果将为紫云英还田减缓稻田温室气体排放提供关键的还田量参数参考。.（2）发现CH4排放通量较高时红萍覆盖可降低由于紫云英秸秆还田导致的CH4排放，同时对N2O排放无显著影响。该结果可在紫云英还田降低稻田N2O排放的基础上通过红萍覆盖减少CH4排放提供依据。.（3）稻田CH4排放与土壤中铵态氮、pH、Eh和氮素残留率有显著的相关关系；稻田N2O排放与铵态氮、Eh和碳、氮素残留率有显著的相关关系，是稻田土壤N2O排放的关键因子。.（4）紫云英还田降低了绿肥还田期产甲烷菌的数量，紫云英还田在氮肥替代率大于20％时增加了水稻分蘖期产甲烷菌数量。而施氮肥降低了绿肥还田期和水稻分蘖期产甲烷菌的数量和群落丰富度。田间水深和总碳是影响稻田土壤产甲烷菌群落结构的主效环境因子。.（5）紫云英还田增加了水稻分蘖期氨氧化古菌AOA和氨氧化细菌AOB数量。土壤总C和总N是影响稻田土壤AOA群落结构的主效环境因子，含水量是影响稻田土壤AOB群落结构的主效环境因子。