Sex matters: understanding wood–leaf hydraulic coordination in dioecious species in a drying world

Sexual dimorphism in dioecious species can shape divergent hydraulic strategies in response to environmental stress, yet integrative studies linking anatomical and physiological traits across different plant organs remain scarce. We investigated sex-specific water-use strategies in two Mediterranean shrubs, Pistacia lentiscus L. and Rhamnus alaternus L., by analyzing leaf and wood anatomy, leaf functional traits, gas exchange and chlorophyll fluorescence. Male plants of both species exhibited conservative morpho-anatomical traits, including smaller, thicker leaves, lower specific leaf area (SLA), higher dry matter content and reduced intercellular spaces, traits typically associated with drought resistance strategies. In P. lentiscus, these traits correlated with higher photosynthetic rates and Fv/Fm values, alongside greater stomatal density and vessel frequency, suggesting coordinated investment in carbon gain and hydraulic efficiency/safety. Conversely, females displayed acquisitive traits (higher SLA, wider intercellular spaces, lower vessel frequency), potentially enhancing photosynthesis under mesic conditions but increasing vulnerability to drought-induced embolism. In R. alaternus, female individuals maintained higher net photosynthesis and instantaneous water- use efficiency, while males exhibited greater Fv/Fm and a decoupled leaf-wood coordination. These findings suggest that males may adopt safer hydraulic architectures, while females, potentially constrained by reproductive demands, pursue efficiency-driven strategies, still maintaining vessel redundancy in wood. As aridity intensifies in Mediterranean regions, such dimorphism may influence population dynamics, sex ratios and species resilience. Our results underscore the ecological significance of species-specific sex-based hydraulic variation and the necessity of incorporating sex into trait-based models of plant responses to climate change.