How Useful Are Plant Traits in Explaining Variation in Phyllosphere Microbial Abundance and Composition Across Hosts?

Plant taxonomy has emerged as a key driver of plant-microbe associations, but the mechanisms underlying these associations remain poorly understood. By defining selective environmental gradients for microbial taxa, plant traits can provide more proximate explanations of microbial taxonomic turnover across plants than plant taxonomy alone. Whether key plant traits may generally predict plant-microbe associations, however, remains unknown. Here, we conducted a systematic review of the phyllosphere literature to evaluate whether specific plant traits consistently explained variation in the abundance and composition of leaf microbes within and among plant species. Drawing on results from over 100 studies, we showed that plant traits linked to development, primary metabolism and defence consistently shaped the composition of leaf bacterial and fungal communities, highlighting the relevance of these traits in predicting plant-microbe associations in the phyllosphere. Since most plant traits tested did not influence leaf microbial composition more frequently than expected by chance, our study underscores the importance of: (1) rethinking the scale and selection of plant traits used to investigate microbiome assembly; (2) refining the taxonomic resolution at which microbial communities are analysed and (3) considering alternative explanations such as stochastic processes or historical factors for improving our understanding of plant-microbe associations.