Abstract:

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 δ D 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.

Key words: stable isotopes, woody plants, soil water, subcutaneous water