岩土剖面构型对喀斯特坡地植物根系吸水的影响机制研究

Karst ecosystem is very fragile and sensitive to environmental change. The mechanism of coupling and response between rock-soil-vegetation and hydrology is complicated because of various microhabitats as well as dual structure of hydrological processes. At present, the theoretical research on relationships between soil water and plant transpiration is still inadequate. This project will be conducted in typical natural secondary forest lands in a karst area, using field monitoring，plot experiment and hydrogen and oxygen stable isotope technique. The purposes of this project are 1) to investigate the effects of steric configuration of rock-soil profile on root water uptake; 2) to analyze soil water dynamics and soil water availability of variform soils; 3) to determine the contributions of soil water and karstic water on plant water sources; and 4) to explore the interactions between soil water and plant transpiration in different karst profiles filled with soils and regolith materials. The results will contribute to a better understanding of plant water resources and its adaptability to various earth surface landforms, and will also provide scientific reference for the utilization of water resources and the management of rock-desertification.

西南喀斯特山区是我国主要的生态脆弱区之一。由于岩石裸露，土层浅薄，地表地下二元水文结构发育，喀斯特生态系统岩石-土壤-植被-水文耦合作用复杂，现有研究还难以阐明异质生境中的土壤-植被水分传输过程，尤其是对不同岩土环境中植物的水分适应机理尚缺乏清晰的认识。本项目拟以喀斯特坡地乔灌次生林为研究对象，通过野外定位观测、盆栽试验和氢氧稳定同位素分析等手段，研究岩土剖面构型对植物根系吸水的影响，分析沟状、面状以及裂隙土壤的水分有效性差异，确定植物根系对不同岩土剖面构型土壤水与岩溶水的吸收利用比例，探讨不同厚度土壤与基岩风化物组合剖面下的植物根系分布与耗水规律，揭示复杂岩土环境中的土壤-植被水分互馈机制。研究结果将深化对喀斯特坡地生态水文过程的认识，促进水土资源的高效利用，为石漠化的综合治理提供科学依据。

喀斯特山区地貌复杂、小生境类型多样，土壤与岩石交错分布，认识不同岩土介质土壤水分变化与植被耗水的关系、基岩风化层的水分供给能力及其对植物根系吸水的影响是植被恢复的关键。本项目针对喀斯特山区不同岩土环境植被耗水机制展开研究，明确了典型坡面岩石-土壤空间分布，获取了不同岩土类型土壤水力学参数，基于Hydrus模型阐释了基岩风化物与土壤混合介质水分运动规律，对比分析了不同介质植被生长与根系发育的特点，评价了岩土混合介质水分有效性及典型植物的水分利用效率。结果发现喀斯特坡地土石界面突变接触，不同小生境类型土壤厚度差异显著，土壤质地以壤质砂土和砂质壤土为主，土壤空间变异受随机因素影响较大。泥岩风化物在不同程度削弱土壤的持水能力，风化物在其含量不足50%时有促进土壤水入渗，超过之后的则阻碍水分入渗。岩土混合介质中风化物含量可以促进植物根系生长，但纯风化物由于养分供应不足会极大限制植物根系发育；岩土混合介质无产无效水占比最大，基岩风化物能够通过改变土壤水分有效性阈值调节水分“产”“效”水平。本研究为深入理解喀斯特山区植物对岩土介质水分变化的适应机制提供科学支撑，对区域水土资源的高效利用与植被恢复有重要意义。