农田土壤碳氮微生物转化的非专性过程及驱动机制

Non-specific transformation processes of extraneous carbon and nitrogen determine the nature of soil carbon and nitrogen cycles and in turn the sustainable management of soil fertility function and the efficient use of nitrogen fertilizer in agricultural ecosystems. However, the microbial engagement strategy and driven mechanisms involved in the processes still remain unclear in science. Hence, based on the simulated incubation and in situ long-term isotope labeling experiment, this proposal was designed to investigate systematically the non-specific microbial transformation processes of carbon and nitrogen and related driven mechanisms by the integrated application of the isotope differentiation technique of the “new” and “old” microbial residues/metabolites and the approaches of DNA-SIP and 13C PLFAs. We aimed at evaluating the engagement strategy and successive engagement processes of different microorganisms at community/genetic and functional levels. The active microbial functional groups are to be identified by substrate utilization strategy of microorganisms. The microbial transformation efficiency and functional timeliness are analyzed through the successive dynamics of microbial communities. The contributions of microbial residues to carbon and nitrogen sequestration are evaluated by the interpretation of different transformation processes of typical carbon and nitrogen substrates. The driven mechanisms of the non-specific transformation processes of carbon and nitrogen can be deduced by the interactive relationships of carbon and nitrogen coupling/decoupling effects and the protection and stabilization roles of microbial residues and/or metabolites. The objective of this study is to validate the long term significance of non-specific transformation processes of soil carbon and nitrogen and related driven mechanisms, and then provide regulating fundamentals for sustainable managements of carbon and nitrogen in agricultural soils.

土壤碳氮微生物转化的非专性过程决定农田土壤碳氮循环特征及肥力功能，但对该过程中微生物参与策略和驱动机制的认识仍是瓶颈问题。本研究以东北典型农田土壤为对象，将模拟培养、原位示踪和长期定位试验相结合，把基于基因/群落水平的微生物功能分析技术和新老微生物代谢物同位素区分技术相结合，系统研究不同活性/组成碳氮底物的微生物转化过程和驱动机制。通过分析微生物底物利用策略甄别功能微生物；通过跟踪微生物群落演替动态分析土壤碳氮转化的时效性；通过微生物增殖-死亡周转的累积效应，评价微生物功能和土壤碳氮转化过程的关联；通过解析碳氮耦合和去偶作用的底物依赖关系以及土体微域效应对微生物代谢的影响，探讨土壤碳氮同化-矿化过程的驱动机制。最后利用长期定位试验以验证土壤碳氮微生物转化的长期效应，阐明微生物过程的适应性机制，以期通过对土壤碳氮转化非专性过程定向调控的认识，为农田土壤碳氮的高效管理提供理论依据。

针对土壤碳氮微生物转化非专性过程中微生物参与策略和驱动机制认识的瓶颈问题，本项目以农田土壤为研究对象，将模拟培养、同位素原位示踪和长期定位实验相结合，综合运用从基因水平到群落水平的功能微生物系统分析技术和新老碳氮有机组分区分技术，研究了农田生态系统土壤碳氮转化的微生物过程和驱动机制。研究取得的重要结果如下：（1）在高活性底物同化过程中，发现了土壤碳氮转化过程受到微生物响应到群落（细胞）代谢周转的双重控制作用。在基因水平上，营养级策略是细菌底物选择性的主要控制因素，并具有进化保守性；真菌对底物的利用具有广谱性，并在种属水平上存在自我调控作用。在群落水平上，发现微生物饥饿效应控制的底物高效利用策略，并通过微生物增殖-死亡周转调控土壤碳可利用性，微生物群落向真菌的演替和真菌残留物积累控制着土壤有机碳稳定化过程。（2）发现了土壤微生物群落通过非专性过程同化外源底物并调控土壤有机质分子组分形成的多元化特征，以碳水化合物和含氮化合物周转为核心调控土壤有机质内循环过程。（3）在复杂底物利用过程中，微生物通过分泌胞外酶使复杂底物各组分以逐级代谢中协同共代谢的方式分解，同时调控碳氮转化过程和供需平衡。细菌对复杂底物初期分解的贡献显著高于真菌，而真菌残留物可接替细菌残留物积累在土壤中并达到平衡状态。（4）在土体微域尺度上，发现微生物和物理化学保护作用共同调控土壤氮库的积累和稳定化过程。砂粒和黏粒是肥料氮素微生物同化的“热点”，砂粒级中的肥料氮素和秸秆氮素不断向黏粒级迁移，并以微生物残体积累为核心促进了两种氮素在黏粒中的稳定化。（5）通过秸秆还田长期定位试验，验证了微生物功能和土壤碳氮转化过程的关联。发现长期秸秆还田可诱导相关功能微生物群落和功能基因变化协同增强土壤微生物的底物分解潜能，调控外源碳氮在土壤中的转化、固持和长期积累过程。本项目的研究成果可为农田土壤碳氮的高效管理及调控提供理论依据。