氮添加对农田土壤碳氮排放与作物残体分解转化的微生物驱动机制

Farmland ecosystems is an important part of terrestrial ecosystem, which are the most active carbon (C) sinks, and have a far-reaching impact on global climate change. In order to obtain higher crop yield, farmland in China receives excessive nitrogen (N) fertilizer for a long time. However, it remains controversial about the mechanism of farmland C and N emission and fixed strategy under N addition. Thus, understanding the effect of N addition on soil C and N emission and crop residues decomposition, the key progress that links plants and soil in the ecosystem, can provide valuable information for soil nutrients cycle. In this study, we continuously monitor the soil C and N emission in farmland planted with winter wheat (Triticum aestivum L.) , which has been fertilized with different N addition rates, to clarify the effect of N addition on soil C and N emissions. To examine the decomposition pattern of crop residues under different N addition rates, we plan to conduct both in suit and indoor residues decomposition experiment, and analysis the residues decomposition characteristic in different N addition, and discuss the effect of N addition on crop residues nutrient release. Besides, to assess the effect of N addition on soil microbial community, we plan to detect the soil microbial composition and functional diversity of different N rates, and links the correlation between soil microbes with crop residues decomposition and C and N cycle, which can help us reveal the microbial mechanisms on soil C and N cycles under long-term N addition and provide important information for understanding the C and N cycles of farmland ecosystem.

农田生态系统作为陆地生态系统的重要组成部分，其碳库平衡对全球气候变化有着深远影响。由于片面追求粮食产量，我国农田长期处于氮肥过量的状态，生态系统碳氮循环密不可分、相互影响，而目前农田生态系统碳氮循环过程对氮添加的响应机制尚存在争议，仍需加强氮添加对农田土壤碳氮排放与作物残体分解转化的驱动机制研究。本研究以不同氮添加水平的旱作麦田为研究对象，通过连续定位监测生育期土壤碳氮排放及其生物与非生物因子动态，明确土壤碳氮排放对氮添加的响应及其生物学驱动机制；通过田间原位与室内模拟作物残体分解实验相结合的方式，阐明作物残体分解与养分释放过程，探讨不同氮添加水平对作物残体养分释放策略的影响机制；通过分析不同氮添加水平对土壤微生物群落结构和碳氮代谢功能的改变，揭示氮添加调控碳氮排放与作物残体分解的微生物学驱动机制，为进一步明确氮添加下农田生态系统碳氮循环过程提供理论依据。

我国农田长期处于氮肥过量的状态，因此研究农田生态系统碳氮循环过程对氮添加的响应机制有重要意义。本研究以不同氮添加水平的旱作麦田为研究对象，通过连续定位监测生育期土壤碳氮排放及其生物与非生物因子动态，田间原位作物残体分解实验，以及土壤和秸秆表面微生物群落结构和功能的分析，明确了氮添加对农田生态系统碳氮排放与转化及其微生物驱动机制。主要取得以下进展：一是明确了不同氮添加水平下旱作麦田土壤碳氮排放的动态变化特征，氮添加促进了土壤碳氮排放且表现出季节性与年际变异，合理施氮对减少温室气体排放具有重要意义；二是揭示了不同氮添加水平下小麦残体碳氮分解转化的策略，结果表明施氮促进了秸秆的分解，土壤碳排放与秸秆失重之间存在显著的线性正相关关系，秸秆的化学性质对施氮量的敏感性不同，土壤温度与水分及秸秆氮含量和秸秆碳氮比是影响秸秆分解的主要因素；此外，施氮对秸秆分解具有阈值效应，过量施氮不仅不会促进秸秆分解过程中养分的归还，还可能增加农田土壤的碳排放，加剧温室效应。三是阐明了不同施氮处理小麦残体分解过程中表面微生物群落结构与功能的变化，结果表明氮添加虽然没有显著改变秸秆表面微生物的群落结构组成，但是通过调控秸秆的理化性质，进而通过秸秆表面微生物的分解功能调控着秸秆的分解速率，进而影响着农田生态系统养分循环过程。我们的研究为进一步明确合理施氮对农田生态系统碳氮循环过程的重要性提供理论依据。