Sex-specific interactions shape root phenolics and rhizosphere microbial communities in Populus cathayana

We assessed root phenolics and rhizosphere microbiomes of Populus cathayana females and males in the replicated 30-year-old plantations, including pure female plantations (PF), pure male plantations (PM), and mixed female and male plantations (MS) to reveal sex and neighbor effects, and associations between root phenolic metabolites and root-related microbes. The phenolic composition of females varied more between intrasexual and intersexual interactions compared to that of males. Thus, sexual dimorphism was present in the metabolic composition and biochemical plasticity. MS plantations enhanced the bacterial and fungal alpha diversity of both females and males. The composition of fungal communities of females and males in MS plantations was different from that in PF and PM, while such differences were not found in the composition of bacterial communities. Bacterial and fungal diversities were correlated with concentrations of specific phenolic metabolites and were most positively responsive to root benzoic acid and pinoresinol production, respectively. Our findings indicate that sex-specific interactions affect the system of plant sex - root phenolics - rhizosphere microbes, and they may contribute to sex-specific resource utilization patterns. Knowledge of such mechanisms would be helpful when establishing plantations of dioecious plants.