黄土高原植被恢复过程中凋落物分解策略及其微生物驱动机制

Litter decomposition plays a key role in the nutrient cycle of terrestrial ecosystem, which release nutrients and affect the carbon (C) fluxes, and has gained increased attention in recent years. ‘Grain-for-Green’ project has been conducted to establish grass or tree cover by removing crops. These abandoned croplands will experience an immediate change from crop to forest or other secondary vegetation, accompany by the evolution of the plant community. Thus, understanding the mechanism of driving litter decomposition, the key progress that links plants and soil in the ecosystem, can provide valuable information for soil nutrient accumulation, ecosystem management, and greenhouse gas emissions in vegetation recovery process. In this study, to examine litter decomposition pattern differs along with vegetation succession, which affected by both soil nutrients and litter quality, we conducted in suit litter decomposition experiment, analysis the decomposition characteristic of different recovery stage, selected the most fitted model for different recovery stage. And we conduct indoor incubation experiments with removing the interference of small-scale environmental factors to detect the warming, drought, N and P addition effects on litter decomposition, to revel how litter decomposition response to climate change and nutrient availability change along with recovery process. Besides, we detected the soil microbial composition and functional diversity of different recovery stage to assess how shifts in the microbial community cause changes in microbial functions during recovery stage and in turn further influence litter decomposition and the process of recovery, and to unravel the mechanisms of nutrient cycling along with the vegetation recovery. Finally, clear the process of vegetation recovery in climate change condition and understand the theoretical basis for the carbon cycle.

凋落物分解是生态系统的核心过程，影响着生态系统碳平衡，在陆地生态系统养分循环中起着重要作用。随着退耕还林（草）工程的实施，黄土高原植被覆盖方式发生了显著改变。因此，研究不同恢复阶段植被凋落物分解策略的转变及生物与非生物驱动机制，对探究植被恢复过程中生态系统碳循环有着重要意义。本研究以黄土高原次生植被自然恢复序列为对象，通过野外原位凋落物分解实验与室内模拟分解实验相结合，分析不同恢复阶段植被凋落物分解特性，筛选不同恢复阶段凋落物分解最优模型；探讨不同恢复阶段凋落物可分解性与土壤分解者主导因素的转换策略；通过模拟气候变化与外源养分添加对凋落物分解的影响，揭示不同恢复阶段凋落物分解对气候变化的响应机制，探讨养分限制学说在凋落物分解中的适用性；同时分析不同恢复阶段土壤微生物群落结构与功能的变化，揭示凋落物分解过程中的微生物学驱动机制，为明确气候变化背景下旱区植被恢复过程中碳循环过程提供理论依据。

植被演替过程中，植被类型、土壤理化性质及土壤微生物群落结构都在发生着协同变化，然而长期演替过程中土壤微生物群落结构和功能如何改变尚不明确。本研究以自然恢复160年的次生演替序列为研究对象，探究了不同演替阶段土壤中凋落物分解能力的差异，同时利用扩增子和宏基因组测序探讨了不同演替阶段土壤微生物群落结构和功能与凋落物分解的关系。研究结果表明，凋落物分解速率随着植被恢复的进行表现出下降的趋势，氮添加促进了植被恢复早期凋落物的分解，但是抑制了顶级群落凋落物的分解速率，表明凋落物分解的养分限制模式随着植被恢复发生了改变；氮磷添加对凋落物有机氮释放没有影响，但是氮添加抑制了凋落物中氮的释放，表明植被恢复过程中凋落物的分解受到了凋落物质量，土壤养分和酶活性的共同影响；土壤细菌和真菌群落在演替前期发生了显著改变，但从先锋乔木林阶段（约110年）到顶级群落辽东栎林（约160年）变化不大，并且真菌表现出较高的变异性；相比于凋落物性质，细菌和真菌群落的变化与土壤理化性质关系更为紧密；土壤微生物功能的变化与微生物的系统发育有关，然而在演替后期微生物群落结构没有显著变化的情况下，微生物的基因功能仍可以发生了显著改变；微生物碳循环基因丰度的降低与凋落物分解能力的下降有关。研究结果意味着在营养丰富的土壤中，微生物的高呼吸作用并不一定代表微生物较高的分解能力，还取决于相关基因的丰度、酶活性和凋落物的理化性质等。在项目执行期间，发表被论文15篇，其中被SCI收录14 篇，主要发表在 Soil Biology and Biochemistry、Biology and Fertility of Soils，Catena，Ecological Engineering， Land Degradation & Development，Geoderma，Agricultural and Forest Meteorology，Journal of Plant Nutrition and Soil Science，Agriculture, Ecosystems and Environment，生态学报等期刊上，参加全国性学术研讨会16人（次），培养研究生 5名，其中博士研究生 3 名。