青藏高原“黑土滩”退化草地中秃斑块的水热空洞效应及其加速草地退化的机制

The bare patch of the alpine meadow is the core problem for the ecological process of ‘bare land’ degraded grassland’s formation and its ecological restoration on the Qinghai-Tibet Plateau. We use the new perspective of ‘hydrothermic-hole’ of bare pitch to re-address the function of bare patch in ecological mechanism of formation of grassland degradation, and put forward the hypothesis that the bare patch accelerating the speed of grassland degeneration through the mechanism of hydrothermic-hole physical effect, soil variation, biological process. In order to examine our hypothesis, we are going to carry out the following study content through investigation of field trip, fixed monitoring experiment in field, laboratory modeling, and laboratory analysis etc. They are, (1) verifying the effect of ‘hydrothermic -hole’ by bare patch in degraded grassland; (2) studying the mechanism about the bare patch led the drying process of sward layer of meadow surrounding bare patch, peeling of sward layer and soil degradation; (3) revealing the interacting effect between bare patch and burrowing activity of rodents, which promoting the bare patch extending and spreading; (4) analyzing mechanism of bare patch contribute to planting, regeneration, and creeping of the poisonous-weed by the hydrothermic variation and soil nutrition change in bare patch. During all experiments, we will use the stable istope technique of 137Cs, 15N, 13C to quantify the ecological process and mechanism of bare path’s effect accurately. Meanwhile, we will use the area of bare patch as the variables to model the relationship between the bare patch variation and ‘bare land’ formatting process through data synthesis of all experiments of hydrothermic physical mechanism, soil science, biological science in this project. The result of our research should enrich the ecological theory of alpine meadow on Tibetan plateau, and reveal the ecological mechanism of ‘bare land’ degraded grassland deeply. The more important purpose of our study is that the result can provide the basic scientific data and guideline for ecological restoration and effective control of about more than 70 million Chinese mu of ‘bare land’ degraded grassland on Tibetan plateau.

秃斑块是青藏高原“黑土滩”退化草地形成、生态恢复的核心问题。本项目以“水热空洞”新视角，通过野外调查、定位，实验室模拟、模型分析等途径，研究黑土滩秃斑块加速高寒草地退化的水热物理学、土壤学、生物学机制。主要内容包括，（1）验证秃斑块的“水热空洞”效应；（2）研究秃斑块水热空洞导致周边草甸草毡层干化、剥离，土壤退化的机制；（3）分析秃斑块与鼠洞相互激荡，促进秃斑扩张、连片的生态学过程；（4）探寻秃斑块水热变化和土壤变化促进毒杂草定植、更新、蔓延的机理。同时采用137Cs、13C、15N等同位素技术，精确量化上述生态学过程，并以秃斑块面积为变量，研究秃斑块变化与“黑土滩”形成的水热物理学、土壤学、生物学等相互关系的生态模型。课题结果，预期能够丰富高寒草地变化的生态学理论研究，深入认识“黑土滩”形成机制，并为青藏高原7000多万亩“黑土滩”的生态恢复、有效治理提供科学依据。

在青藏高原黑土滩极度退化草地形成过程中，“秃斑水热空洞效应及加速草地退化的机制”是基于高寒地区草地生态学，水热物理学，植物-土壤系统化学生态学等交叉学科角度提出并证实的理论，是青藏高原高寒草地退化研究前沿领域。.课题通过4年野外调查、实验室测试、数据分析等工作，主要得到以下结论和成果：（1）秃斑化导致壤容重、总孔隙度、导管空隙度、田间持水量、入渗率以及生长季的蒸散发变化异常，使得裸露土壤的水热属性与大气变化同步性增强，水热通量加剧，当秃斑大于2.2 m2时，水热通量呈现线性增加趋势，形成水热空洞效应，逐渐与大面积黑土滩趋同。（2）秃斑造成小生境的水热加剧流动，造成周边草甸的干化加剧，并具有显著的方向性，干化作用致使秃斑边缘的紧实度和剪切力减小，使其更容易遭到破坏和侵蚀，在秃斑边缘只需6 N的剪切力就可以将其破坏，增加了鼠类动物侵入几率，加剧了草毡层下垫面形成空层，进一步加速了草毡层干化、剥离。（3）秃斑5m2面积时秃斑内毒草群落逐渐稳定，秃斑开始主动扩张，黑土滩秃斑块开始加速草地退化进程。（4）黑土滩秃斑内退化草地土壤微生物群落均偏好利用酯类、氨基酸类及胺类碳源，毒草植物的根系分泌物与根际微生物之间直接的或间接的互作很强，毒草分泌不同的根系分泌物与土壤微生物进行互作，从而促进了其在黑土滩中的蔓延。（5）黑土滩秃斑的土壤质地为砂质壤土或粉砂质壤土，从秃斑的空间结构、土壤质地、养分的尺度性分析，黑土滩的秃斑块在扩张过程中，土壤系统稳定性逐渐下降，促使小秃斑容易向规则的大斑块发展，最终形成大面积的黑土滩。（6）该课题共发表相关论文22篇，学术会议论文1篇，专著1部；授权国家发明专利2件，科研奖励1个，参加8次国内外学术会议，毕业硕士研究生5名，在读博士生2名，研究成果支撑了青藏高原目前1.65亿亩黑土滩极度退化草地的生态恢复工程。