黄河源区沙漠化过程对土壤碳迁移/释放影响研究

Aeolian desertification changes the budget of soil carbon, decreases soil carbon storage, and promotes CO2 emission into the atmosphere by physical (wind erosion), biological, and coupled physical-biological processes, then contribute to the regional even the global climate change and environment change. The present research mainly focuses on the impact of wind erosion on the movement of soil carbon in the arid and semi-arid area. The relevant research, especially the influence of aeolian desertification biological process on soil carbon release, has not been conducted enough on the Qinghai-Tibetan Plateau, where is one of the significant soil carbon pools in the world. Therefore, the Yellow River Source Area, affected by the severest aeolian desertification, is selected as the study area for this project to stand for the Qinghai-Tibetan Plateau. In this research, the different types and grades of aeolian desertified alpine grasslands are supposed to substitute the various development stages of aeolian desertification. The wind erosion process, biological and environmental factors, and soil respiration in the different types and grades of aeolian desertified alpine grassland plots will be observed and measured. Depending on the observation and measurement, three groups of quantity relations, are expected to be set up. They are the relationships between wind erosion rate and soil carbon horizontal movement, between biomass and soil organic carbon, and between ecological factors and soil respiration, separately. Then, this project will try to understand how soil carbon moves horizontally, how soil carbon release vertically, and how soil carbon storage change. Finally, the total amount of soil carbon move and release due to aeolian desertification will be estimated basing on the remote sensor monitoring and the field observation and measurement data. This research strives to contribute to the knowledge of carbon cycle, scientifically calculate the carbon storage on the Tibetan Plateau, and provide the theoretical foundation for accurately managing the alpine grassland.

沙漠化通过物理、生物和物理-生物耦合过程改变土壤碳收支，降低土壤碳储存，并通过促进CO2释放，影响区域甚至全球气候变化。目前相关研究主要集中在干旱半干旱区风蚀过程对土壤碳水平迁移的影响。在全球重要土壤碳库-青藏高原开展沙漠化过程导致碳释放的研究则有限。本项目选择青藏高原沙漠化最为严重的地区-黄河源作为研究对象，利用空间上发展程度代替时间上发展过程的方法，对不同类型和程度沙漠化土地风蚀特征、生态特征和土壤呼吸进行定点观测和分析，通过建立不同程度沙漠化土地风蚀速率与土壤碳素迁移，生物量与土壤有机碳含量以及生态系统各要素与土壤呼吸的定量关系，揭示沙漠化过程中土壤碳水平迁移，垂直释放和储量变化的发展规律，并结合沙漠化土地的遥感监测结果初步估算近30年黄河源区沙漠化发展过程中的碳迁移和释放量。该研究不仅有助于认识青藏高原碳循环过程，科学估算青藏高原碳储量，还有助于为高寒草地的科学管理提供理论依据。

沙漠化主要通过物理、生物和物理-生物耦合过程改变土壤碳收支，减少土壤碳储存，并通过促进CO2释放，影响区域甚至全球气候变化。本项目选择黄河源不同发展程度的沙漠化土地作为研究对象，通过风沙活动长期定点观测和模型模拟，认识物理过程对土壤碳素水平迁移的影响；通过土壤和植被特征、土壤呼吸和NEE的观测及分析，揭示沙漠化生物过程对土壤碳储量变化以及物理-生物耦合过程对土壤碳释放的影响机制；以不同时空分辨率的遥感影像作为数据源，恢复黄河源区沙漠化土地时空变化过程，并结合定点观测和模型模拟结果估算黄河源区沙漠化发展过程中土壤碳素迁移和土壤碳释放量。研究结果表明：1）黄河源区沙漠化土地占总面积4.5-6.1%，主要分布在玛多县黄河乡、扎陵湖乡及共和盆地。2）轻度沙漠化草地0-50厘米深度的SOC含量显著增加了2-5%，中度、重度和严重沙漠化阶段的SOC显著下降了34-65% ；轻度沙漠化草地的SOC增加主要来自群落结构改变导致的地上生物量增加；中度沙漠化草地SOC减少是由于地表和土壤温度增加以及土壤水分减少导致分解速率增加引起的；重度和严重沙漠化草地的SOC主要受进入土壤中的有机物降低以及风蚀影响。3）高寒草地土壤呼吸随沙漠化程度加剧呈先增加后降低的变化趋势，在中度沙漠程度达到最大值；土壤温度与土壤呼吸之间呈指数关系，但不同沙漠化程度下土壤呼吸对土壤温度的敏感性不同；主要是由不同沙漠化程度的土壤温度、地下生物量以及SOC的差异造成。4）沙漠化草地水平输沙率为0.25-700kg/m2/y，相应的水平碳迁移速率分别为0-3.5 kg/m2/y；沙漠化导致黄河源区土壤碳年平均迁移量为16-21Tg/y；因沙漠化导致土壤有机碳通过垂直释放的损失量为0.007g/m2/y，整个源的总损失量为4.6-5.3Tg/y。本研究揭示了沙漠化对生态系统碳循环的影响机制，不仅有助于认识青藏高原的碳循环过程，科学估算青藏高原碳储量，还有助于为高寒草地的科学管理提供理论依据。