Stable Isotopic Study on Water Utilization Sources of <i>Pinus yunnanensis </i>Plantations in the Central Yunnan Karst Plateau

Abstract

In order to explain the water utilization mechanism of Pinus Yunnanensis plantations in the Central Yunnan Karst Plateau, SW China, and their adaptive strategies to arid karst habitat, the authors collected and analyzed the stable 18O isotope values of stem water of Pinus Yunnanensis in Bajiang valley, and their accompanying trees and bushes and their potential water sources. The IsoSource model was applied to compute the probable contribution of multiple potential water sources to total plant. The results show that in the ecosystem of Pinus Yunnanensis plantations, there exists significant evaporative isotopic fractionation during the process of hydraulic infiltration from precipitation to ground water and soil water and that of hydraulic redistribution in the soil profile. Water utilization positions and proportions of Pinus Yunnanensis and its accompanying trees and bushes vary from season to season, and they are evident competitors for water. During dry seasons, mature Pinus Yunnanensis uses 68.6% of 0-55cm soil water while the contribution of 30-110cm soil water and groundwater to the young Pinus Yunnanensis reaches 55.8% and 31.7% respectively. In rainy seasons, the use ratio of 0-55cm surface soil water by young Pinus Yunnanensis, Pistacia weinmannifolia and Rhododendron spiciferum are 63.1%, 56.3% and 86.2% respectively while the mature Pinus Yunnanensis uses rainfall, groundwater and fog droplets of canopy interception.