Warming reverses intersexual interactions: a shift from competition to facilitation in the dioecious mulberry tree

Abstract Understanding how global warming reshapes intraspecific interactions is critical for predicting plant performance and ecosystem stability in a rapidly changing climate. Dioecious plant species, with distinct female and male individuals, are foundation species in many forest ecosystems, yet how sexual interactions respond to climate warming remains poorly understood. Here, we conducted a greenhouse warming experiment using Morus alba as a model to examine how warming alters sexual interactions, by comparing growth, physiological traits, and nutrient acquisition in inter-sexual (female–male) and intra-sexual (female–female and male–male) plantings. Warming reversed the direction of intersexual interactions: inter-sexual combination shifted from strong competitive suppression under ambient temperature to facilitation under warmed condition, yielding higher total biomass and nutrient pools than either intra-sexual combination. This facilitative shift was associated with warming-induced changes in root growth in mixed-sex plantings, enhanced photosynthetic performance in female plants, and synergistic increases in whole-plant nutrient pools. Our findings indicate that the outcome of sex-based intraspecific interactions is highly context-dependent and provide experimental evidence that sexual interactions shift with climate warming. This study highlights the importance of maintaining sexual diversity to enhance productivity and resilience in dioecious plant populations under future climate warming.