施氮和增雨对温带草原群落水平凋落物分解及土壤有机碳形成的影响

Litter decomposition is a major determinant of carbon and nutrient cycling in terrestrial ecosystems. Most of the existing decomposition studies exploring its response to nitrogen deposition and precipitation were only based on single-species litter, which, however, could not predict the mixed litter decomposition rate at community level. Increased nitrogen deposition and precipitation can also change plant biomass and community-weighted litter quality, which will alter the quantity and quality of litter inputs to soil. However, the responses and the associated inherent mechanisms of community-weighted litter decomposition and soil organic carbon formation to nitrogen addition and increased precipitation have rarely been addressed. In this proposal, as part of a long-term global change multiple-factor experiment in Inner Mongolia, a two-factor experiment will be conducted to simulate nitrogen addition and increased precipitation. Three types of litter decomposition experiments will be established to investigate the effects of microbial and microclimates, community-weighted litter quality and their combination on litter decomposition at community level. A field incubation experiment will also be conducted by decomposing litter mixture collected from each treatment on the surface of carbon-free model soil in their ‘home’ plots. Litter decomposition rate and soil carbon content will be measured to explore the responses of community-weighted litter decomposition rate and soil carbon formation efficiency to nitrogen addition and increased precipitation. The associated inherent mechanisms and their relative importance will further be separated, which will provide us a new insight into carbon and nitrogen cycling in grasslands under future global climate change.

凋落物分解是陆地生态系统碳循环和养分循环的重要周转过程，该过程响应氮沉降和降雨变化的研究多集中于植物个体水平，但单种凋落物分解不能准确预测群落水平混合凋落物分解的响应。施氮和增雨也会改变植物生物量和群落水平凋落物性质，影响凋落物向土壤输入的数量和质量。关于施氮和增雨对群落水平凋落物分解的影响及机制和对土壤有机碳形成影响的认识仍非常匮乏。本项目拟基于内蒙古多伦长期全球变化多因子实验平台，选取施氮和增雨两因素交互处理，设置三种凋落物分解实验，探讨施氮和增雨对凋落物分解影响的微生物及环境效应、凋落物性质效应和综合效应。另将四种处理下相应的混合凋落物置于不含碳模式土壤上，进行野外原位培养。通过测定凋落物分解速率和土壤碳含量等，区分施氮和增雨调控群落水平凋落物分解的内在机制，阐明其对凋落物输入质和量的改变如何影响土壤有机碳形成，为从生态系统尺度研究草地碳氮循环响应全球变化提供科学依据和数据支持。

凋落物分解是陆地生态系统碳循环和养分循环的重要周转过程之一，其响应施氮和增雨的研究已相对较多，但大多研究仅考虑单种凋落物分解，未能准确预测群落水平混合凋落物分解对全球变化的响应。施氮和增雨可以通过改变土壤温湿度、微生物生物量及群落组成、凋落物性质等多个方面影响分解，但以往研究未能分离其影响群落水平凋落物分解的微环境效应、凋落物性质效应及其综合效应。本项目旨在探究施氮和增雨对群落水平凋落物分解的影响及其潜在作用机制。基于项目计划书，本研究在内蒙古多伦长期全球变化多因子实验平台设置三种凋落物分解实验，包括（1）将单种凋落物放置于不同实验处理下，以探究微环境效应；（2）将分别取自不同实验处理下的混合凋落物均置于对照处理下，以探究凋落物性质效应；（3）将分别取自不同实验处理下的混合凋落物均置于原位进行培养，以探究综合效应。定期取样测定凋落物干重剩余量及理化性质等。同时，连续三年测定不同实验处理下植物生物量和凋落物生物量等指标，并计算群落水平凋落物层存留时间。项目执行期间取得如下重要进展：施氮和增雨均会通过改变微环境而提高单种凋落物分解，通过改变凋落物性质而降低分解速率，最终正负效应抵消，对群落水平混合凋落物分解无影响。同时，长期施氮会显著延长凋落物层存留时间，主要因为施氮提高了相对更难分解的禾草植物的相对比例，而增雨对凋落物层存留时间无影响。研究结果对深入理解草地生态系统群落水平凋落物分解过程及机理具有重要科学意义。项目执行期间，项目负责人发表第一作者SCI论文一篇。