Professor Université du Québec à Montréal, Quebec, Canada
Leaf-associated bacteria in the phyllosphere of plants play key roles in mediating the ecology and evolution of their hosts and in ecosystem function. Although global patterns of microbial diversity have been quantified in systems such as soils, oceans and animal guts, we lack broad-scale data on the diversity and biogeography of plant-associated bacteria, which limits our understanding of the drivers of plant-microbe interactions and ability to predict their responses to global change. Here we identified bacterial communities using high-throughput sequencing of the 16S rRNA gene for a total of 1453 leaf samples from 329 plant species from 10 forest sites across major biomes in China. We quantified the relative importance of a range of factors including host attributes, abiotic environments, neighborhood plants and spatial proximity potentially driving phyllosphere bacterial diversity using variation partitioning. We estimated bacterial host specialization and investigated the ecological and evolutionary determinants of host specificity. We constructed metacommunity-level plant-bacteria association networks, identified keystone bacteria taxa and modeled the abundance of these keystones as a function of host, environment and climate.
We showed that host plant, abiotic environment, space, and plant neighborhood effects jointly explained the majority of variation in phyllosphere bacterial diversity. With increasing latitude, the importance of host to explain bacterial diversity increased strongly while the confounding effects among variables decreased. Most phyllosphere bacteria were host-specialized, and the degree of host specificity was related to the bacteria phylogeny and traits. Host specialists were more prevalent at lower latitudes and on locally rare plant species. We revealed a set of metacommunity-level bacterial keystone taxa that structure the large-scale plant-bacterial association network, whose abundance was mainly controlled by climate, host and spatial proximity. Taken together, our findings provided the most comprehensive understanding to date of the patterns and mechanisms of plant-associated bacterial diversity. Host plant is a major control of bacterial community structure on leaves, and bacterial specialization on hosts was associated with plant local abundance, highlighting the role of plant-bacterial interactions in structuring the composition of both plant and bacterial communities. Our results suggest avenues for predicting and managing plant microbiomes in natural ecosystems under global change.