黄土高原辽东栎枯落物不同界面分解过程及对土壤有机碳的贡献机制

The implementation of "Grain for Green" project promoted the increase of soil organic carbon in the Loess Plateau. The accumulation of litter is one of the main reasons for the accumulation of soil organic carbon. Due to the obvious layered structure of forest litter, the interfacial reactions between litter and humus layer or soil layer are the main mechanism to determine the decomposition rate of litter and the turnover of organic carbon. At presentation, the coupling relationship between different interface microorganisms and soil organic carbon from different sources is still unclear during the litter decomposition process. In this study, the litter bag experiment was used to study the decomposition characteristics of litter under different interfaces. The isotope labeling was used to quantify the distribution ratio of litter organic carbon in soil and microorganisms, clarifying the contributions of plant litter to soil organic carbon. The contribution of microbes to organic carbon was determined by the biomarkers at different interfaces, identifying the biomass sources of soil organic carbon. The microbial community structure, associated with biomarkers and the chemical compositions of organic carbon under different interfaces were analyzed, clarifying the relationship between microbes and soil organic carbon at different interfaces, which reveals the contribution mechanism of plant litter to soil organic carbon. Our results will improve the litter decomposition theory, verify the mechanism of microbes on soil organic carbon, and provide theoretical support for the recovery of vegetation on the Loess Plateau.

退耕还林（草）工程的实施促进了黄土高原土壤有机碳的增加，枯落物累积是土壤有机碳积累的主要原因。由于森林枯落物存在明显的层状结构，其界面反应（腐殖质层、土壤层）是决定枯落物分解快慢与有机碳周转的主要机制。目前，枯落物分解过程中，不同界面微生物与与不同来源的土壤有机碳的耦合关系尚不明确。本研究采用枯落物分解袋法研究枯落物在不同界面下的分解特征，通过同位素标记量化枯落物有机碳在土壤、微生物体中的分配比例，阐明枯落物有机碳对土壤有机碳的贡献；通过测定不同界面下的生物标志物，辨析土壤有机碳的生物质来源；分析不同界面下的微生物群落结构，结合生物标志物与有机碳的化学机构，建立微生物类群与有机碳的耦合关系，阐明不同界面下微生物群落主导的有机碳固持机理，揭示枯落物碳对土壤有机碳的贡献机制。研究结果将完善枯落物分解理论，明晰微生物与土壤有机碳的作用机制，为黄土高原植被恢复管理提供理论依据。

植物枯落物作为土壤有机碳的主要来源之一，其分解过程对植物初级生产力、生物地球化学循环至关重要，尤其是土壤有机碳周转过程。微生物作为植物枯落物分解的主要驱动力，其分解速度及分解过程显著影响土壤有机碳的形成与累积过程。结果表明，真菌和细菌对植物枯落物分解具有同等重要的地位，其群落演替是枯落物分解过程中有机碳释放与累积的主要机制。微生物一方面通过分泌胞外酶降解有机碳，导致有机碳化学结构发生明显的变化，尤其是芳香碳的累积，烷基碳的减少。同时，微生物又可通过同化代谢，合同有机小分子化合物，经过体内周转后以死亡残体形式的形成土壤有机碳。随着植被年限的增加，植物枯落物逐年累积导致植物枯落物出现层状结构，也导致枯落物分解速率发生了显著变化，由此驱动的有机碳周转机制也出现了显著差异。不同界面微生物群落差异及演替规律是枯落物有机碳释放与累积的主控因子。因此厘清枯落物分解过程中微生物群落结构及功能有助于地阐明有机碳循环过程，为精确调控陆地碳库具有重要的意义。