Non-structural carbohydrates (NSC) are essential for the osmotic adjustment and maintenance of the hydraulic functioning of trees, but knowledge about the relationship between NSC dynamics and hydraulics during drought stress is still limited, especially in dioecious plants.

We investigated photosynthetic carbon assimilation, xylem hydraulics and related functional traits, and explored whether hydraulics are linked to NSC dynamics in the leaves and branches of Populus euphratica females and males along an aridity gradient in the Xinjiang Province, China.

Both sexes of P. euphratica had increased intrinsic water use efficiency (WUE), percent loss of conductivity (PLC) and xylem pressure inducing 50% loss of hydraulic conductivity (P₅₀), but decreased net photosynthetic rate (P_n), sapwood-specific hydraulic conductivity (K_s) and hydraulic safety margin (leaf mid-day water potential-P₅₀, HSM₅₀) associated with the reduction in the soil water content. Furthermore, females and males have different hydraulic strategies related to NSC dynamics under low soil water content conditions. Males had higher K_s, wood density (WD), HSM₅₀, P_n, WUE, leaf dry mass per area (LMA) and leaf soluble sugar levels, and lower branch soluble sugar levels, PLC and P₅₀ values than females under extreme drought conditions, indicating that males had a more resistant xylem and can maintain water flow and leaf turgor probably due to the greater availability of soluble sugars to be used for osmotic adjustments. In addition, females had a lower K_s, WD and LMA and higher branch soluble sugar levels and PLC, implying that females were more vulnerable to cavitation and required higher branch soluble sugar levels for embolism repair under extreme drought conditions.

Synthesis. Due to the spatial sexual segregation across resource gradients, dioecious plants are more vulnerable to rapid climate change. The different hydraulic strategies linked to NSC dynamics between females and males may result in a situation that one sex is more prone to an increasingly long and intense drought than the other one. This study improves our predictions for future climate change impacts on dioecious P. euphratica and provides theoretical knowledge for restoration and afforestation in P. euphratica forests.