秸秆还田条件下水稻根际土壤反硝化作用及其功能微生物演替机制研究

Denitrification in rice paddy rhizosphere soil is an important step in the environmental nitrogen cycle, which can can cause a loss of nitrogen (N) from soil as well as the emission of nitrous oxide (N2O), contributing to global warming. Straw return has been widely recommended as an environmentally friendly practice for recycling of agricultural resources in agricultural ecosystems. Returning straw which serves as an important carbon source into soil can potentially improve the nutrient status of agricultural soils, influencing the microbial community involved in soil denitrification. However, influence of straw return on the denitrification and succession mechanism of functional microorganisms in rice rhizosphere soil is relatively unknown. In this study, rice pot experiments combined with rhizo-bag will be performed in greenhouse simulating rice field ecosystem with addition of wheat straw. The response mechanisms of N2O emission, denitrification rate and the ratio of N2O to N2 emission to straw return will be revealed based on a greenhouse air collection device and 15N isotope technique. More importantly, a systematic research will be carried out about the abundance, community composition and diversity of denitrifying bacteria using modern microbiological molecular ecology technologies. Following statistical analyses of soil properties, microbial communities, and N2O emission, the main functional microorganisms and control factors regulating denitrification of rice rhizosphere and non-rhizosphere soils with straw return will be revealed. Above all, influence of straw return on denitrification and succession mechanism of functional microorganisms in rice rhizosphere soil will be revealed. This study will provide new insights into improving the nitrogen-fertilizer use and decreasing N2O emission in paddy soils when straw is returned into field.

水稻根际反硝化作用对稻田生态系统氮循环起到关键作用，是稻田氮素损失和N2O排放的重要途径。秸秆还田作为农业废弃物可持续利用的一种方式，在我国广为提倡，然而目前针对秸秆这类复杂碳源施用下水稻根际土壤反硝化作用及其功能微生物演替机制的研究仍相对缺乏。本项目拟选取两种类型水稻土，采用根际袋法开展麦秸还田下水稻盆栽实验。基于温室气体采集系统和同位素示踪法揭示水稻生育期内根际/非根际区N2O释放量、反硝化速率和15N2O/15N2比值对秸秆施用的响应规律；应用现代分子生态技术明确反硝化功能微生物（nirK、nirS和nosZ型）丰度、群落组成和多样性对秸秆还田的响应规律；并结合土壤性质，利用多种统计分析方法，辨析秸秆还田下参与水稻根际/非根际土壤反硝化作用的主要功能微生物及其驱动因子，揭示秸秆还田下水稻根际土壤反硝化作用的微生物学机制，为合理施用秸秆提高稻田氮肥利用率和降低温室气体排放提供理论依据。

水稻根际反硝化作用对稻田生态系统氮循环起到关键作用，是稻田氮素损失和N2O排放的重要途径。秸秆还田作为农业废弃物可持续利用的一种方式，在我国广为提倡，然而目前针对秸秆这类复杂碳源施用下水稻根际土壤反硝化作用及其功能微生物演替机制的研究仍相对缺乏。该项目围绕典型氮素循环过程-反硝化作用及其功能微生物演替机制，以水稻根际/非根际土壤为研究对象，选取两种类型稻田（高砂土和黄泥土）为供试土壤，综合应用土壤化学、微生物学及分子生物学等手段，结合室内土壤淹水培养实验和温室水稻盆栽实验研究了秸秆还田条件下水稻根际土壤反硝化作用过程及其功能微生物演替机制。研究发现，淹水培养条件下，两种类型稻田土壤中3种类型的反硝化菌（nirK、nirS和nosZ型）群落组成是显著不同的，与未施用秸秆的土壤相比，秸秆还田显著改变了两种类型土壤反硝化菌群落结构，土壤易氧化有机碳（EOC）是土壤反硝化菌群主要调控因子；基于水稻盆栽实验进一步研究发现，秸秆施用显著促进了黄泥土水稻根际土壤反硝化速率，并显著提高了黄泥土根际土壤nirS和nosZ的丰度；与黄泥土所不同，秸秆还田显著降低了高砂土水稻根际土壤反硝化速率以及nirK、nirS和nosZ丰度；基于高通量测序技术研究发现，秸秆还田显著改变了黄泥土根际土壤nirK、nirS和nosZ型反硝化菌群落结构和高砂土根际土壤nosZ型反硝化菌群落结构，但并未显著改变高砂土根际土壤nirK和nirS型反硝化菌群落结构。研究结果阐明了秸秆还田下水稻根际土壤反硝化作用及其功能微生物演替规律，为合理施用秸秆提高稻田氮肥利用率和降低温室气体排放提供了理论依据。