Sex-specific phosphorus (P)-use and -acquisition in dioecious Populus euphratica as affected by soil moisture levels

Dioecious plants show sexual dimorphism in their phosphorus (P) availability responses. However, the understanding of sex-specific strategies for P utilization and acquisition under varying soil moisture levels remains unclear. Here, we assessed a range of root functional traits, soil P properties, total foliar P concentration ([P]), and leaf chemical P fractions – inorganic P ([Pi]), metabolite P ([PM]), lipid P ([PL]), nucleic acid P ([PN]), and residual P ([PR]) – as well as other leaf functional traits in female and male trees under different soil moisture levels (25% for high and 7% for low). Our results showed that females had larger specific root length (SRL) under well-watered conditions, resulting in greater root foraging capacity. This led to a 36.33% decrease in soil active inorganic P in the rhizosphere and a 66.86% increase in total foliar [P], along with all five foliar chemical P fractions ([Pi], [PM], [PL], [PN], and [PR]) compared to males. However, males exhibited significantly higher photosynthetic P utilization efficiency (PPUE) than females. Especially under low soil moisture levels, males exhibited a significant reduction in soil active organic P, coupled with a large increase in the exudation of soil phosphatases and carboxylates. Furthermore, the proportion of metabolite P in total foliar [P] was 41.96% higher in males than in females. Mantel and Spearman correlation analyses revealed distinct coordination and trade-offs between foliar P fraction allocation and below-ground P acquisition strategies between the two sexes. Leveraging these sex-specific strategies could enhance the resilience of dioecious populations in forest plantations facing climate-induced variability.