短期增温对祁连山北部多年冻土生态系统二氧化碳交换及土壤微生物的影响

The permafrost regions are sensitive to climate change. The hydro-thermal conditions of soils in permafrost regions will change along with the increasing temperature, and therefore, have effects on carbon cycle. However, it is remains unknown about the effects of increasing temperature on the CO2 exchanges between ecosystems and air, and also little is known about the response of soil microbial communities to temperature changes in permafrost regions. This project will select the wet meadow, meadow and steppe ecosystems in the permafrost regions in the Qilian Mountain area as studying area. The ecosystem respirations and CO2 net ecosystem exchanges of the ecosystems under 3 years experimental warming using open top chamber (OTC) will be compared with those of controls to study the effects of warming on the CO2 exchange in permafrost regions. The bacterial and fungi population and diversity of the soil samples will be analyzed using high throughput sequencing, thus the effects of short term warming on microbial communities will be investigated. The hydro-thermal conditions of soils under experimental warming and controls will be monitored continuously. In addition, the soil physio-chemical variables will be analyzed. Based on these data and the mechanisms of CO2 exchange and soil microbial process, the statistical analysis will be used to study the mechanisms of possible hydro-thermal conditions in the changes of CO2 exchanges and soil microbial communities under experimental warming. The results will provide useful parameters for models of global warming and carbon cycle, as well as shed light on the carbon sink-source relations in permafrost ecosystems under global warming scenarios. In addition, the results will also be helpful for the study of environment protection and grassland management in permafrost regions.

多年冻土区对气候变化敏感，温度增加会改变多年冻土区土壤的水热过程，进而影响到碳循环。但到目前为止，增温对多年冻土区生态系统呼吸及其与大气CO2净交换和土壤微生物有何影响还不清楚。本项目选择祁连山地区沼泽草甸、草甸和草原三种生态系统类型，对比增温3年和未增温样地的生态系统呼吸及CO2净交换量，研究短期增温对生态系统碳的源汇效应的影响；采集土样，利用高通量测序技术研究微生物群落，分析细菌和真菌的群落结构多样性特征，研究不同生态系统类型下土壤微生物对温度升高的响应。研究同步监测增温和未增温样地的土壤水热情况，分析土壤pH等理化指标，通过统计分析，讨论增温对多年冻土区生态系统CO2交换和土壤微生物产生影响的可能水热作用机制。研究结果可为区域气候变化和碳循环模型提供参数，有助于认识气候变化背景下多年冻土区生态系统碳的源汇效应及微生物的响应过程，还可为多年冻土区生态环境保护及草地资源管理提供科学依据。

多年冻土区对气候变化敏感，温度增加会改变多年冻土区土壤的水热过程，进而影响到碳循环。但到目前为止，温度增加对多年冻土区碳循环和土壤微生物有何影响还不清楚。本项目按照申请书计划，选择野外不同的多年冻土和植被类型的样地为研究区，结合开顶式增温手段，开展了多年冻土区土壤碳含量与动态、生态系统呼吸、生态系统碳净交换、土壤细菌群落的结构动态及其与环境因子关系的研究。结果表明：1）多年冻土区温度升高会促进植被生长，生态系统吸收更多的碳，目前整体上祁连山多年冻土区在气候变暖情况下碳汇能力会增强；2）气候变暖和多年冻土退化会导致多年冻土区碳的分解速率加快，多年冻土退化导致的水分降低和温度升高是主要的物理机制，同时，多年冻土退化不仅会引起热喀斯特地貌而直接导致地表土壤侵蚀加剧，多年冻土退化和植被退化还会降低多年冻土区河流中碳的浓度，但是产流效应增加，会增加碳的流失，且这部分碳可分解性很强。因此，气候变暖和多年冻土退化整体上会减少多年冻土区土壤碳储量减少；3）多年冻土区各不同植被类型下细菌的优势种主要为变形菌门、酸杆菌门和拟杆菌门等常规种群，增温和多年冻土会改变壤pH和水分会发生变化而土壤细菌群落结构发生变化。此外，热融滑塌不仅改变土壤中碳含量，还会破坏土壤的垂直结构而改变土壤中细菌群落结构的垂直分布。这些微生物的改变也会进一步影响多年冻土碳循环的过程。在本项目的支持下，研究结果发表了18篇学术论文，其中SCI论文10篇，中文核心8篇；培养了4名硕士生。两名硕士生毕业论文被评为校优秀硕士毕业论文，一名被评为甘肃省优秀硕士论文。