西南喀斯特地区地表地下二元结构明显,地表水渗漏、地下水深埋,即使降水充沛,但依然存在严重季节性干旱,土层浅薄、分布不连续,储水能力低,因此,水分亏缺是西南喀斯特地区植被迅速恢复与生态重建的主要障碍[1-3]。喀斯特地区特殊的地质背景和复杂的地形地貌,水分运移过程有别于其他地区,且不同类型喀斯特地貌类型土壤水分运移规律差异也很大[4-5]。喀斯特地区水资源的合理开发利用和生态环境保护[6],对深刻理解其生态水文过程有着极大的诉求。虽然喀斯特地区生态水文学在植被水分来源与耗散机理、坡面水文过程、环境变化的生态水文效应等方面取得了重要进展,并构建了多种模型[7-9],但在喀斯特地区植被-水分-土壤的耦合关系的响应机制方面的研究较少,无法为喀斯特地区生态治理、环境保护和水资源合理利用等提供更有利的理论依据和技术支撑。
近年来,随着研究方法和观测手段的不断改进和日趋完善,特别是由于稳定同位素技术的快速发展和应用,为深入开展水分限制生态系统中植物对水分资源的利用、混生群落中物种间对水资源的竞争和共生关系以及根系对土壤水分的调节机理的研究提供了一种新的有效途径。氢氧同位素在水循环过程中存在分馏现象而产生不同的氢氧同位素值,可以作为水分迁移的天然示踪剂[16],用于确定植物吸收土壤水分的来源[17-18],在我国喀斯特地区环境特殊,生态水文过程对改善生态环境起着不可忽视作用,喀斯特地区土层浅薄,适用于其它区域的植物与水分之间关系的研究方法,在这一区域并不适用,而稳定同位素技术解决了这一难题;生长在这一区域的植物根系发达,它们对水分利用具有季节性变化,雨季时会利用浅表层土壤水,但旱季时利用表层岩溶带水或深层土壤水[19-20]。随着生态建设的加强,人工种植植被与水资源之间需要维持一个可持续发展的关系,氢氧稳定同位素技术可为植被恢复的物种选择提供可靠的方法,使其合理利用水资源,真正改善区域的生态水文环境。
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