Sexual dimorphism in root exudation mediates belowground neighbor recognition and shapes rhizosphere soil microbial assembly

Summary Sexual dimorphism in physiological traits is a hallmark of dioecious plants, yet whether these differences extend belowground to mediate neighbor recognition and rhizosphere microbiome assembly remains largely unexplored. Using split‐root experiments, 13 C‐pulse labeling, and multi‐omics with dioecious Populus cathayana , we dissected the interactions between plant sex, root exudation, and microbiome assembly. We demonstrated that male and female plants discriminate neighbor sex by modulating their root exudation. Females perceiving same‐sex neighbors upregulated defense‐related metabolites, whereas under inter‐sexual interactions they shifted toward growth‐promoting pathways. Males significantly increased the allocation of newly fixed photosynthetic carbon to the rhizosphere. Specifically, 13 C incorporation into bacterial and fungal phospholipid fatty acids (PLFAs) was markedly higher when males grew in female‐conditioned soil compared to male‐conditioned soil. This male‐driven carbon investment fostered highly interconnected cross‐kingdom microbial networks with a significantly higher proportion of positive associations. Consistently, females grown under inter‐sexual interactions exhibited greater nitrogen contents and higher photosynthetic rates than those under intra‐sexual interactions. Our findings demonstrated that sexual dimorphism in root exudation drives the assembly of more complex and positively connected microbial networks, providing a transformative framework for understanding how belowground sexual recognition enhances the ecological resilience and productivity of mixed‐sex plant populations.