中文摘要：

中国南方喀斯特区气候湿润,但土层浅薄,土被不连续,储水能力差,水分成为限制因子,土层下广厚基岩为植物根系生长提供了空间,形成其独特的水分机制。采用氢氧稳定同位素技术与测定植物清晨水势的方法,选取贵州南部荔波茂兰国家级自然保护区内的喀斯特原生林、次生林及因人类砍伐退化的喀斯特灌丛,分析测定其中4种常见优势木本植物小枝木质部水分及土壤水、表层岩溶带水氢氧同位素值的相关性,确定植物水分来源,并通过相关模型计算水源贡献比;探讨喀斯特森林生态系统中植物水分利用策略。结果表明：无论雨季或旱季,表层岩溶带水是喀斯特植物的稳定水源。各植被类型都主要利用土壤水,在降水减少的10月,灌木林和原生林对表层岩溶带水的用量比例提升,而次生林对土表水的用量更高。不同物种有不同的水分利用策略,常绿小乔木香叶树利用表层岩溶带水比例最高,显示其较深的根系;而落叶乔木圆果化香表现为较浅的根系和干季表土水利用比例较高的特征。

英文摘要：

Ecosystems in the karst region of southwest China are very fragile due to thin soil layer and intensive infiltration capacity of rock fracture, which result in a very limited amount of water storage for plant uptake. Water retention in the soil zone and shallow fractured rock zone （subcutaneous） is a key factor for plant growth. Distinction of water sources taken by karst plants is a challenging task for botanists and hydrologists but is needed for ecosystem management. In this study, stable isotope analysis was used to investigate water sources for plants because of no isotopic fractionation during water uptake by terrestrial plants. We selected several dominant plant species in three forests of mostly primary forest, secondary forest and bush covers at the Maolan national nature reserve of karst ecosystem in a small catchment of Libo, south Guizhou of China. Proportions of water sources for plant uptake were determined by the 8D and δ18O values of plant stem water, and water taken from soil layers and the subcutaneous zone. The analysis reveals that water was mainly taken from the soil layers and to less degree the subcutaneous zone as well. In October with scarce precipitation, plants in the bush and primary forest were prone to take more water from subcutaneous zone, while plants from secondary forest were prone to take more water from the upper layer of soil. Different species had different water use strategies, Lindera communis took a larger proportional water from the subcutaneous zone, suggesting deeper roots. However, Platycarya longipes extracted more percentage of water from the s upper soil water because of its shallower roots.