Soil evaporation and plant water use strategy of riparian forests in extremely arid deserts, northwestern China: a stable isotope perspective

Introduction In extreme arid regions, Populus euphratica ( P. euphratica ) and Tamarix ramosissima ( T. ramosissima ) play vital ecological and landscape roles, but their survival and regeneration are severely limited by water scarcity. Since soil evaporation and plant transpiration represent the major pathways of water loss in these ecosystems, quantifying soil evaporation rates and clarifying plant water-use strategies are crucial for supporting vegetative growth and maintaining population stability. Methods This study investigated water movement in P. euphratica , T. ramosissima , and their mixed stand using multi-source isotope data collected from June to September. Results Soil evaporation exhibited consistent patterns across all stands, being most pronounced in the shallow layer (0–40 cm) and declining exponentially with depth, while the deep soil layer (>200 cm) was primarily recharged by groundwater. Although vegetation type introduced some variability in evaporation rates, these differences did not reach statistical significance. Both species primarily extracted water from the 100–300 cm soil layer and groundwater, with P. euphratica relying more heavily on soil water at 100–200 cm depth and T. ramosissima utilizing more groundwater, reflecting its greater drought tolerance. In mixed stands, this divergence in water use intensified interspecific competition, resulting in lower soil moisture and a more rapid decline in groundwater levels compared to pure stands, a phenomenon linked to differences in root distribution. Discussion To maintain the structure of desert riparian forests, ecological water conveyance must be carefully managed to sustain groundwater levels within a suitable range for vegetation. Such management would help prevent T. ramosissima dominance and facilitate the survival, regeneration, and sustainable development of P. euphratica .