大兴安岭地区兴安落叶松林蒸散对冻土冻融的响应机制研究

The Greater Xingan Mountains is the most important water conservation sites and ecological shelterbelt of North-east China. However, with the intensification of climate change and human activities in recent years, the temperature has been increasing ,the permafrost boundary has been moving northward, resulting in an overall degradation of the regional environment and gradual change of the forest ecosystem in the Greater Xingan Mountain region. Up to present, few study has been conducted on the interaction between forest vegetation and frozen soils. Under the special climatic regimes of the cold temperate zone, the interaction/coupling mechanism between forest evapotranspiration and permafrost freezing/thawing process is still a scientific question to be elucidated. Here ,we choose the larch(Larix gmelini) forest and permafrost in Greater Xingan Mountain region as the research subject. On basis of our former established longterm observation plots located at different sites / forest stand types,we will measure and monitor the sap flow, canopy interception and soil water storage, then calculate the forest evapotranspiration in different periods according to the the water balance theory. Moreover, we will analyze the spatial and temporal variation of forest evapotranspiration and permafrost freezing/thawing. Based on the monitoring on the freezing and thawing of permafrost in different sites and forest stand types, the spatial and temporal variation of permafrost freezing / thawing processes will also be analyzed. Through correlation analysis and linear mixed regression models,we will explore the coupling relationships between the forest evapotranspiration and permafrost freezing /thawing processes, and disclose their influencing factors. After finishing this project, we expect to understand the interaction mechanism of the forest evapotranspiration to the freezing / thawing process of permafrost in the Greater Xingan Mountain region, providing a theoretical guidance to the scientific control of regional ecohydrology and ecosystem management of natural forest in this special region in China.

大兴安岭是我国东北地区最重要的水源涵养地和生态屏障，受全球气候变化和人类活动的影响，该地区气温逐渐变暖，冻土界线开始北移，区域环境和生态系统逐渐发生变化。目前，在生态水文研究中很少关注森林-冻土之间的相互作用，而在寒温带特殊的气候条件下，森林蒸散与冻土冻融耦合机制仍是一个没有探明的科学问题。本研究以大兴安岭地区的兴安落叶松林和冻土为对象，通过在不同立地和林分类型中设立观测样地，基于水量平衡原理，观测树干液流、树冠截留和土壤贮水量的变化，计算兴安落叶松林蒸散量。分析兴安落叶松林蒸散的时空变化规律。通过观测不同立地及林型冻土在不同时期的冻融特征，研究冻土冻融的时空变化规律。通过相关分析与线性回归模型等对落叶松林蒸散及冻土冻融的耦合关系及其影响因素进行分析，探讨兴安落叶松林蒸散对冻土冻融的响应规律。阐明兴安落叶松林蒸散和冻土冻融之间作用机制，为该区域生态水文管理和天然林保护与经营提供科学依据。

森林生态系统的蒸散发作为森林水文过程的主要组分，直接影响着区域水分循环和生态系统功能，植被的存在作为隔热层保护着多年冻土的稳定，冻土冻融使得植被在生长季便于吸收土壤水分。大兴安岭多年冻土区处于欧亚大陆冻土带南缘，冻土较薄，对气温升高和外界变化极为敏感，兴安落叶松林与冻土有着非常紧密的相互依存关系。从19世纪以来，大兴安岭落叶松林受全球气候变化和人类活动的影响，气温逐渐转暖，冻土界线开始北移，生态环境逐渐恶化，这使得该地区的森林水文过程和冻土的稳定性受到严重影响。.本研究以内蒙古大兴安岭森林生态系统国家野外科学观测研究站多年积累的长期定位观测的相关数据为基础，通过本项目执行期间的连续观测，系统分析兴安落叶松林蒸散的季节变化规律、年际变化规律和空间变化规律；探讨冻土冻融的时空变化规律；研究影响兴安落叶松林蒸散和冻土冻融各因子的耦合关系，阐述兴安落叶松林蒸散和冻土冻融的响应机制等三个方面的内容。.主要研究结果：（1）兴安落叶松生态系统的生长季有气候更加温暖而干旱的趋势，冻融期则更加温暖和湿润，生长季和冻融期的ET、WUE均微弱减少，VPD在生长季增加，在冻融期减少，生长季贡献了主要的ET；（2）根河流域1980-2017年ET值整体呈微弱增加趋势，ET值年内变化特征是先增大后减小的单峰型分布，主要集中在5-9月份；（3）生长期、完全冻结期、融冻期ET值均呈现增加趋势，始冻期呈降低趋势，生长期的ET值占年内蒸散量的66.19%；（4）兴安落叶松林土壤含水量与蒸散发量呈正相关关系，土壤含水量呈下降趋势。.依托课题，获得国家专利1项，完成博士后出站报告1份，共培养了1名博士、2名硕士、15名本科生，发表学术论文13篇，硕士学位论文2篇。积累了兴安落叶松林四年观测数据、野外样地调查数据，同时掌握了SWAT模型模拟分析方法。通过项目研究，为大兴安岭地区水源涵养地的生态安全提供理论支持。