Diversity and sources of floral microbial communities

Flowers serve as a key ecological interface where microorganisms, plants, and pollinators interact, yet the processes shaping flower microbiota remain insufficiently synthesized. In this review, we summarize the current literature on the assembly and distribution of floral microbiota across floral organs through three major transmission pathways: insect vectors, bird visitation, and aerial deposition. We assess the organ-specific distribution and transmission pathways of microbial taxa across nectar, stigma, petals, pollen, and anthers, and estimate the relative importance of each of these vectors in microbial dispersal. Our analysis reveals a strong research bias toward nectar and stigma, which collectively dominate the studies of floral microbiota. Based on the currently available literature, insect pollinators, especially the honeybees and bumblebees, emerge as the most frequently reported agents of microbial transfer by repeated deposition of microbes onto floral organs. Bird-mediated transmission, despite its geographic restriction, plays a key role in ornithophilous systems, whereas aerial deposition appears to have a comparatively limited influence. We also emphasize the effect of floral microbes on flower attractiveness, phenotypic changes, and the systemic microbial movement within plants. This review incorporates flower ecology, microbiology, and pollination biology, and points out how flowers act as microbial gateways between the aboveground and belowground parts of plants, and how flowers remain underappreciated for their role in systemic interaction between plants and microbes.