土壤氮磷比调控秸秆腐解的微生物学机制

Straw return has been considered as an important soil carbon sequestration measure to ensure soil sustainability and increase crop productivity. However, there remain notable knowledge gaps regarding straw decomposition and its microbiological mechanism under different soil nitrogen phosphorus ratios. This project would primary focus on the microbial transformation process and characteristics of rice straw in paddy soil. By using modern microbial molecular ecology methods, such as real-time quantitative PCR and high-throughput sequencing, and combining with soil enzymology and carbon metabolic fingerprint, the succession rules of microbial community composition and function during straw decomposition would be studied. The relationships between microbial community succession rules and straw decomposition would be explored as well. Meanwhile, stable isotope probe technology (13C-DNA-SIP) would be used to identify the key microbial species involved in the assimilation and utilization of rice straw from two aspects of 16S rRNA and ITS gene. The project tries to test the following questions: (1) how do soil nitrogen phosphorus ratios affect the straw decomposition and the priming effects caused by the decomposition process, and (2) the roles and mechanisms of soil microbial community composition and function on regulating straw decomposition and priming effects. This project will improve the understanding of microbial mechanism related to soil organic carbon mineralization, explore the mechanism of soil fertility improvement under straw return, and provide a theoretical basis for maintaining sustainable agricultural production through nutrient management.

秸秆还田被认为是重要的土壤碳封存措施，用以保障土壤可持续性与提高作物生产力。然而，目前关于不同土壤氮磷比例下秸秆腐解及其微生物学机制尚缺乏足够的理解。因此，本项目以水稻秸秆在水稻土中的微生物转化过程与特征为主要研究内容，利用实时定量PCR和高通量测序等现代微生物分子生态学方法，结合土壤酶学、碳代谢指纹图谱，研究微生物群落组成与功能的演替规律，并探讨它们与秸秆腐解的关系；同时，利用稳定同位素探针技术（13C-DNA-SIP），从16S rRNA 和ITS 基因两方面，鉴定参与秸秆同化利用的活跃微生物类群。项目拟阐明（1）土壤氮磷比如何影响秸秆腐解以及腐解过程中引发的激发效应；（2）土壤微生物群落组成及其功能在调控秸秆腐解与激发效应发生过程中的作用与机制。项目将完善对土壤有机碳矿化相关微生物机制的理解，探明秸秆还田影响下的农田土壤肥力变化机制，为通过养分综合管理保障农业可持续生产提供理论依据。

土壤碳封存被认为是缓解全球气候变化、保障土壤可持续性与提高作物生产力的核心战略。长期氮肥偏施导致土壤氮磷供应比例失衡，进而影响土壤微生物群落及其对秸秆碳等外源有机碳周转的调控。本项目以长期不同施氮水平的水稻土为试验土壤样品，剖析其土壤微生物资源限制特征及主要驱动因素，并以秸秆等为外源有机物材料，研究土壤微生物群落组成及其功能在调控秸秆腐解、碳激发效应等过程中的作用与机制。主要研究进展如下：1. 随着施氮水平的增加，土壤 C：N 化学计量失衡减弱，而 N：P 化学计量失衡增强。土壤微生物群落具有严格的 C：N 和 N：P 化学计量内稳态以及弱的 C：P 化学计量稳态。土壤微生物群落普遍受到碳、磷资源的共同限制，且随着施氮水平的增加，微生物群落的相对碳限制增强。土壤可溶性有机碳含量是预测微生物相对碳限制的最主要因素，微生物量氮磷比和微生物量氮是预测微生物氮或磷限制的最主要因素。2. 外源添加不稳定有机碳后，土壤产生正激发效应，且激发效应强度随着历史施氮水平的增加而增强。外源不稳定有机碳的添加提高了土壤胞外酶活性，缓解了高氮水平处理土壤的碳限制。K策略微生物变形菌门是消耗土壤本底碳的优势菌群，而r策略微生物厚壁菌门是同化利用外源有机碳的主要菌群。微生物胞外酶活性和群落丰富度是预测土壤碳激发效应强度的重要指标。3. 在秸秆腐解过程中土壤微生物群落组成受到历史施氮水平和培养时间的显著影响。细菌中的变形菌门、酸杆菌门、绿弯菌门以及真菌中的子囊菌门是作物秸秆腐解过程中的主导菌群。在秸秆腐解前期，细菌关键类群相对丰度与CO2-C释放量呈正相关，而在秸秆腐解后期，真菌关键类群相对丰度与CO2-C释放量呈正相关。项目明确长期施氮下农田土壤的微生物资源限制模式，完善对外源碳同化相关微生物学机制的理解，探明施肥影响下的农田土壤肥力变化机理，为通过制定科学合理的施肥策略保障农田生态系统土壤有机碳储量、促进农业可持续生产提供理论依据。