Dioecious plants present sexual dimorphism, but how the root traits and nutrient uptake of female and male plants in dioecious species response to the sexual identity change of the neighbor plants are poorly understood.

Mulberry (Morus alba L.), a dioecious plant widely distributed in China, was employed in our study. Male and female plants were grown with neighbors of the same and opposite sex for 3 months. At harvest, the root anatomy, root morphology, nutrient concentrations and biomass accumulation were measured.

When grown with the opposite sex, the males showed decreases in root xylem size, biomass of root and stem and increases in root N, P and K concentrations compared with grown with the same sex. By contrast, females showed significant increases in xylem size, fine root system (e.g. fine root length, root surface area and root volume), root carbon isotope composition (δ 13C) and root N, P and K concentrations. The changes in the δ 13C and N, P and K concentrations in male and female plants were associated with the changes of root traits. These results demonstrated that the sexual identity of the neighboring plants affected root anatomy and morphology of female and male mulberry plants. Meanwhile, the responses of female and male plants to the sex change of the neighboring plants showed sexual dimorphism, which influenced water-use efficiency and resource acquisition. These findings are important for understanding the population dynamics of other dioecious species in forestry and natural systems.