Interspecific competition alters water use patterns of coexisting plants in a desert ecosystem

Background and aims Water is fundamental to the growth of plants by participating in plant metabolism, and nutrient transport and maintaining the integrity of the hydraulic system. Knowledge of water use characteristics among co-occurring plant species is crucial for understanding the ecohydrological processes and community assemblages. However, interspecific interactions with respect to water sources and physiological activity remain poorly understood. Methods The stable oxygen isotope values of xylem and soil water, and leaf physiological characteristics were measured in three communities in the Mu Us Desert, northwest China: a mixed shrub and grasses community; a pure shrub community; and a pure grasses community. Results In mixed communities, the main water source for shrubs shifted to deeper soil layers than in pure communities, whereas grass water use switched to shallower soil layers. Leaf photosynthetic rates, stomatal conductance, transpiration, and water potential of both species were significantly lower in mixed communities than in pure communities. These results suggest that interspecific interactions influenced plant water use patterns. The water-use efficiency of shrubs increased in mixed communities, whereas that of grasses decreased, indicating that grasses exacerbated water stress on shrubs, while shrubs relieved water stress on grasses. Additionally, leaf physiological activity was positively correlated with shallower water sources and negatively correlated with deeper water sources. Conclusion Our findings show that plants responded to interspecific interactions under drought conditions through the coupling of plant water sources with leaf physiologies. The present study provides important insights into water-related reforestation and ecological management in dryland ecosystems.