祁连山青海云杉林土壤呼吸及其组分对冻融变化的响应

A burst of soil respiration is often observed in high-altitude and high-latitude ecosystems during freeze-thaw period. Climate warming is expected to cause more frequent freeze-thaw events in these regions, which would enhance soil respiration and increase the contribution of soil respiration to ecosystem and regional carbon cycle. However, uncertainty still remains regarding the effect of freeze-thaw on soil respiration as well as the involved mechanisms. Therefore, the proposed project will be conducted to investigate the response and involved mechanisms of soil respiration and its components to freeze-thaw fluctuation in Picea crassifolia forests, typical subalpine forests in arid regions with high soil carbon concentration. In the forests, freeze-thaw events occur regularly. Through field observations, controlled experiments and laboratory incubations, we intend to evaluate the effect of freeze-thaw on soil respiration and the contribution of each components, explore the response of heterotrophic respiration to the change of freezing temperature, soil moisture and the duration of freezing, and determine the key factors to control them. Based on the above research, we aim to reveal the response mechanisms of soil respiration to freeze-thaw fluctuations, and provide a scientific basis for predicting the potential impacts of climate change on soil carbon cycling in subalpine forests in arid area. These findings are expected to deepen the understanding of the processes and mechanisms of soil respiration in subalpine forests.

冻融作用对土壤呼吸的“激发效应”被证实在高纬度及高海拔地区的许多生态系统普遍存在。在气候变暖背景下，这些区域将经历更为广泛频繁的冻融作用变化，并可能提高土壤呼吸对生态系统乃至区域碳循环的贡献，但有关土壤呼吸对冻融变化响应及机理的认识仍存在分歧。本项目拟以土壤碳储量丰富、冻融现象普遍发生的干旱区典型亚高山森林—祁连山青海云杉林为研究对象，采用野外原位观测、控制实验与室内模拟实验相结合的方法，开展土壤呼吸及其组分对冻融变化响应的研究，评估冻融作用对土壤呼吸的激发效应及各组分贡献，重点解析土壤异养呼吸对冻结温度、土壤水分含量、冻结时长等冻融过程中关键要素变化的响应规律，确定冻融条件下土壤呼吸组分变化的关键影响因素，揭示土壤呼吸对冻融变化的响应机理，为预测气候变化对干旱区亚高山森林土壤碳循环过程的潜在影响提供依据。研究结果有望深化对亚高山森林土壤呼吸过程及影响机理的认识。

在气候变暖背景下，高海拔及中高纬度地区将经历更为广泛频繁的冻融作用变化，并可能提高土壤呼吸对生态系统乃至区域碳循环的贡献，但有关土壤呼吸对冻融变化响应及机理的认识仍存在分歧。本项目拟以土壤碳储量丰富、冻融现象普遍发生的干旱区典型亚高山森林—祁连山青海云杉林为研究对象，采用野外原位观测、控制实验与室内模拟冻融实验相结合的方法，开展土壤呼吸及其组分对冻融变化响应的研究，得到如下主要结论：①基于沿海拔梯度原位观测观测数据，揭示了青海云杉林生长季、冻融期土壤呼吸过程的时空动态特征，阐明了青海云杉林冻融期土壤呼吸在全年土壤呼吸总量中占有重要份额（27%-36%），且随着海拔的升高这一比例逐渐增加；②采用挖壕沟断根法区分青海云杉林土壤呼吸组分，基于沿海拔梯度原位实验数据，揭示了青海云杉林土壤异养呼吸、根系自养呼吸过程的时空动态特征，阐明了冻融期土壤呼吸各组分的相对贡献（土壤异养呼吸、根系自养呼吸对土壤呼吸的贡献率分别为77%-86%、14%-23%），且随着海拔升高，根系自养呼吸对土壤呼吸的贡献率逐渐下降，而土壤异养呼吸对土壤呼吸贡献率逐渐升高；③借助模拟冻融实验，揭示了冻结温度、土壤水分含量、冻融循环次数等冻融过程中关键要素变化对青海云杉林土壤异养呼吸的显著影响，总体来讲，冻结温度越低，冻结前土壤水分含量越高，融化期土壤呼吸增加的幅度越大，但随着冻融循环次数的增加，融化期土壤呼吸增加的幅度会逐渐降低；④基于对冻融过程中青海云杉林土壤呼吸与生物、非生物环境因子之间关系的综合分析，揭示了冻融过程中青海云杉林土壤微生物群落由贫营养型（Oligotrophs）向共营养型（Copiotrophs）转变是驱动土壤呼吸变化的主要微生物学作用机制，而冻融作用下土壤养分有效性的提高是促使土壤微生物群落组成结构变化的主因。. 基于项目的研究，已在国内外主流期刊发表论文6篇，其中以第一标注发表论文4篇，高效完成了项目的预期研究目标。