水稻根系分泌耦合根际氮素转化的微生物机制

Diverse microorganisms in the rhizosphere play important roles in plant health and soil element cycling. The microorganisms involved in nitrogen cycling processes contribute largely to the nitrogen utilization and N2O emission in agricultural soils, such as paddy soil. However, knowledges about the genotype of critical microorganisms related to nitrogen turnover and the factors influencing the diversity and function of these microorganisms are limited. Focusing on nitrogen cycling in the rice rhizosphere, this project aims 1) to investigate the nitrogen turnover rates and function microbial communities in rhizosphere and bulk soils from different types of soils; 2) to determine the relationship among root exudates, nitrogen turnover rates and functional microbes via 13CO2-continuous labelling experiments. 13C-labelled low molecular weight organic acids will be measured by ion chromatography combined with mass spectrum, and the composition and abundance of critical microorganisms related to nitrogen transformation will be determined by combined 13C-DNA-SIP with Illumina sequencing of related functional gene amplicons; 3) Finally, this project will design a pot experiment amended with exudates to analyze the effect of root exudates on nitrogen cycling processes. Taken together, this project would depict the microbial mechanisms that coupling root secretion with nitrogen transformation in rice rhizosphere, which would provide theoretical basis for nitrogen application and improving nitrogen utilization efficiency in agricultural soils.

氮素转化的微生物过程是影响农田氮肥利用率及氧化亚氮排放的重要因素，根际微生物种类繁多，在植物健康及土壤元素循环中发挥重要作用。然而，根际氮素转化关键功能微生物组成及其影响因素还不明确。因此，本项目将以水稻根际氮素转化为研究核心，首先研究不同类型水稻土根际/非根际氮素转化速率和氮素转化功能微生物差异；进而通过13CO2连续标记实验，量化水稻根系分泌13C标记小分子有机酸及氮素转化速率，采用稳定同位素技术（DNA-SIP）联合Illumina高通量测序技术探明水稻根际氮素转化关键微生物丰度和多样性；最后结合添加根系分泌物培养实验阐释水稻根系分泌物对根际氮素转化过程影响，阐明水稻根系分泌耦合根际氮素转化的微生物机制。本研究成果将为农业氮肥施用、提高氮肥利用率及环境保护提供坚实的理论基础。

本项目以水稻根际氮素转化过程及微生物为研究核心，探究了水稻土中厌氧氨氧化（anammox）和厌氧铁铵氧化（Feammox）过程及其相关功能微生物组成差异；分析了氮素转化功能微生物对根际效应及干湿交替的响应机制，并且阐释了水稻根系分泌物对反硝化过程影响的微生物机制。研究结果表明：（1）不同母质水稻土anammox速率存在显著性差异，且根际anammox速率显著高于非根际；中国南方水稻土中广泛存在Feammox过程，Geobacter、GOUTA19、Nitrososphaeraceae和Pseudomonas是Feammox过程的重要相关微生物，pH和粒径是影响水稻土中Feammox相关微生物群落组成的重要环境因素；（2）水稻土中总微生物与活性微生物群落存在显著性差异，且活性微生物对根际效应响应更加灵敏，反硝化微生物比硝化微生物对根际效应响应更加灵敏；（3）干湿交替将显著影响活性微生物和总微生物群落组成，氮素转化功能微生物对干湿交替过程的响应存在不同响应；（4）水稻根系分泌物（甲酸和葡萄糖）提高土壤反硝化速率，且葡萄糖的促进作用更加强，并发现含水量是影响水稻土中反硝化速率及其功能微生物组成的重要因素。本项目的实施为提高农业生产过程中氮肥利用及环境保护提供了重要的科学依据。