降水变化和氮沉降影响森林叶根凋落物分解研究进展

全球环境变化通过改变凋落物质量和产量、土壤生物以及非生物因子调控森林凋落物分解,从而对森林生态系统物质和能量循环产生重要的影响。就森林凋落物分解对当前我国面临降水格局变化和大气氮沉降增加的响应进行了回顾和系统的分析,发现降水格局改变如降水减少可能降低凋落物质量从而减缓凋落物分解,而氮沉降增加通常提高凋落物质量从而促进凋落物分解（间接效应）;降水格局改变通过调节土壤含水量和溶解氧含量进而影响微生物参与的分解过程,或通过改变可溶性组分的淋溶量来影响凋落物分解的物理过程,而氮沉降增加主要通过提高外源氮素的有效性从而促进或抑制微生物参与的分解过程（直接效应）。现有研究大多是基于地上凋落物（例如叶凋落物）来理解和量化森林凋落物分解速率与环境因子之间的关系。但目前对降水格局变化及其与大气氮沉降增加的交互作用如何影响森林地上和地下凋落物分解,以及潜在的微生物学机制仍然缺乏统一和清晰的认识。从土壤性质、凋落物质量、微生物群落结构和功能3个方面构建了环境变化对森林地上和地下凋落物分解的概念框架,并进一步阐述未来研究的重点方向：（1）亟需查明地上和地下凋落物分解的驱动机制;（2）探明降水格局变化和氮添加单因子及两因子交互作用对凋落物分解和养分释放的影响及其生物化学调控机理;（3）阐明微生物群落结构和功能对降水格局变化和氮添加单因子及两因子交互的响应机制。以期为深入探讨全球环境变化对森林凋落物分解的影响,以及环境胁迫下森林土壤"碳库"维持机制的解释提供科学依据。

Advances in the effects of precipitation regime alteration and elevated atmospheric nitrogen deposition on above- and below-ground litter decomposition in forest ecosystems

Global environmental change regulates forest litter decomposition by changing the quality and yield of litters, soil biotic and abiotic factors, which may consequently induce a large change in nutrient cycling and energy flow in forest ecosystems. Under current and future conditions, terrestrial ecosystems will be experienced to concurrently multiple global change drivers, which pose challenges for understanding and projecting terrestrial carbon-climate feedbacks. This article presented a comprehensive review and analysis of the responses of forest litter decomposition to two naturally co-occurring anthropogenic global change drivers, precipitation regime alteration and atmospheric nitrogen (N) deposition. We found that environmental changes could affect litter decomposition via direct and indirect pathways. A changing precipitation regime, such as decreased precipitation, may indirectly suppress litter decomposition by altering initial litter quality, while N enrichment usually stimulates litter decomposition by increasing litter initial quality. Precipitation regime alteration can also influence microbial catabolism processes by changing soil moisture and oxygen diffusion, and/or alter the processes of leaching, while the addition of N stimulates or inhibits the processes of microbial catabolism by directly changing the external nitrogen availability. Therefore, we infer that the interaction of precipitation regime alteration and N deposition may have multiplicative, synergistic or antagonistic effects. Although many previous studies contributed to understand how single global change factor affect litter decomposition, there have been few studies aimed at understanding how precipitation regime alteration and atmospheric nitrogen deposition interactively affect litter decomposition in forest ecosystems. Moreover, most of the existing studies focused on the characterization and quantification of environmental factors on the leaf litter decomposition rather than root decomposition. We further developed a conceptual framework of the above- and below-ground litter decomposition under the context of precipitation regime alteration and atmospheric N deposition and also took soil properties, litter quality, and microbial community structure and function into consideration. We finally proposed that future studies on forest litter decomposition should focus on: 1) explain the mechanisms driving the above- and below-ground litter decomposition; 2) explore the effects of precipitation regime alteration and N addition, and their interaction on the forest litter decomposition rate and nutrient release; and 3) elucidate how precipitation regime alteration and N addition, and their interaction influence microbial community structure and function. These studies will improve our understanding of the mechanisms of above- and below-ground litter decomposition in response to global changes, and the maintenance mechanisms of the soil "carbon pool" under global changes condition.