草灌植被转变对草地生态系统及其水碳过程的影响研究进展

气候变暖和过度放牧的共同作用使全球草地出现明显的灌丛化现象，灌木去除是草地灌丛化控制的重要方式，识别这些草灌植被转变对生态系统、生态水文、土壤侵蚀和侵蚀碳流失的影响对草地可持续管理具有重要意义。综述了草地灌木入侵及其控制对植物群落和土壤功能(如土壤有机碳)的影响，以及这些草灌植被变化对生态水文、土壤侵蚀和土壤侵蚀碳流失等水碳耦合过程的影响机制。针对目前草地灌木入侵和去除对植物群落、植被格局、水土过程和功能影响研究的薄弱环节，对未来相关研究提出以下建议：(1)需深化草灌植被转变对碳、氮等生物地球化学循环的影响机制研究，(2)需重视核磁共振光谱、生物标志物、同位素等新技术和植被格局的指数与连通性等新方法在草灌植被转变的水、碳等生态效应研究中的应用，(3)需加强草灌植被格局和生态水文、土壤侵蚀与土壤侵蚀碳等水碳过程的多要素、多过程和多尺度的综合研究。本文旨在为灌丛化草地科学有效的生态恢复与多目标的土地利用管理提供理论支撑。

Research progress on the effect of the transition between shrub and grass vegetation on grassland ecosystem and its water-carbon processes

The combined effects of overgrazing and climate warming drive shrubs to encroach into grassland ecosystems worldwide, while removal of the shrub is an important controlling measure for shrub encroachment. It is meaningful for sustainable grassland management to identify the impacts of transitions between grass and shrub vegetation on the ecosystem, eco-hydrology, soil erosion, and soil erosional carbon loss. In this paper, we reviewed the effects of shrub encroachment and its removal on the plant community and soil function (e.g., soil organic carbon), and the impact mechanism of these transitions between grass and shrub vegetation on the water-carbon coupling processes such as the ecohydrological, soil erosional, and erosional carbon loss processes. According to the weakness of previous research on the impacts of shrub encroachment and its removal control on plant community, vegetation pattern, and soil-water processes and functions, we provided several suggestions for future research directions:further studying the influence mechanism of transitions between grass and shrub vegetation on biogeochemical cycles such as carbon and nitrogen cycle, paying more attention to applying new techniques such as nuclear magnetic resonance (NMR) spectroscopy, biomarker, isotopes, and methods (e.g., indicators and connectivity of vegetation pattern) to determine the ecological effects of water and carbon for transitions between grass and shrub vegetation, and strengthening the multi-factor, multi-process and multi-scale comprehensive study among grass-shrub vegetation pattern and water-carbon processes such as eco-hydrology, soil erosion and soil erosional carbon loss. These can provide theoretical support for scientific and practical ecological restoration and multi-objective land-use management of shrub-encroached grassland.