Seasonal Variations in Water Use Strategies in a Karst Region

ABSTRACT Karst regions exhibit heterogeneous water distribution attributable to their unique topographical features. Research concerning water absorption, efficiency dynamics and the underlying mechanisms within commercial plantation forests remains limited, which constrains our understanding of ecohydrological processes. In this study, three typical commercial forests ( Juglans regia , Prunus salicina and Prunus persica ) were selected as research subjects. We investigated seasonal variations in water uptake patterns and water use efficiency (WUE) of each species by combining stable isotopes (δ 2 H, δ 18 O and δ 13 C) with the MixSIAR model. We hypothesise that these forests adjust their water absorption depth in response to seasonal variations in water availability, consequently influencing WUE. Our results showed that the most important water source for J. regia and P. salicina was 0–30 cm soil water, contributing 55% and 41.6%, respectively. Groundwater provided the next highest contributions, at 25.2% and 30.6%, respectively. In contrast, P. persica mainly used groundwater in spring and autumn (51.2% and 42.3%), 30–60 cm soil water and 0–30 cm soil water in summer (39.5% and 39.1%). Groundwater is an indispensable water source for commercial forests, with a minimum use proportion of 18.8% in summer and a maximum that can reach 51.2% in spring, highlighting the ‘stabiliser’ role groundwater provides during seasonal droughts in karst areas. The WUE of P. persica is significantly higher than that of J. regia during the spring and autumn seasons ( p < 0.05). These results suggest groundwater is a crucial water source for commercial forests in humid subtropical zones, and vegetation with a greater dependence on groundwater exhibits a higher WUE. This study elucidates the ecological strategies employed by subtropical karst commercial forests to adapt to variations in soil moisture by flexibly adjusting their water absorption depth. The findings provide a scientific basis for the rational allocation of water resources within commercial forests in this region.