Phyllosphere microbiome, including both epiphytic and endophytic components, is an important part of forest ecosystems. Like other ecological communities, phyllosphere microbial communities are shaped by both niche-based deterministic processes and neutrality-based stochastic processes. Understanding the relative importance of these two processes in determining phyllosphere microbial assembly is essential, but has not been explored. Moreover, host plant diversity may alter the assembly of the phyllosphere microbial communities through changing the relative importance of the selection and neutral processes. How host plant diversity influences the diversity and structure of phyllosphere microbial communities is still poorly understood. In this study, we collected leaf samples from the BEF-China experiment, where tree species richness was experimentally manipulated in a replicated design ranging from one-species monocultures to 24-species mixtures. Both epiphytic and endophytic bacteria were extracted, and their diversity and community structure were quantified using high-throughput sequencing. By analyzing patterns of bacterial diversity at the plot- and sample-level, and the compositional difference in community structure among samples, we aimed to (1) identify leaf epiphytic and endophytic bacterial diversity patterns along the gradient of host plant diversity, (2) explore the ecological drivers of variation in leaf epiphytic and endophytic bacterial diversity and community structure, and (3) examine how the relative importance of deterministic and stochastic processes changes with host plant diversity.
Results/Conclusions
Our study revealed three important findings. First, plot-level diversity of both epiphytic and endophytic bacteria increased with host plant diversity, but these similar patterns were driven by different mechanisms. The increased diversity of epiphytic bacteria in higher-diversity plots was driven by increased sample-level bacterial diversity, whereas the increased diversity of endophytic bacteria in higher-diversity plots was driven by increased beta diversity among samples. Second, the identity and functional traits of host plants were most important in shaping leaf endophytic bacterial community assembly, whereas both host species identity and dispersal limitation strongly influenced leaf epiphytic bacterial community assembly. Third, the relative importance of deterministic processes increased with host plant diversity. Our study revealed different assembly mechanisms of leaf epiphytic and endophytic bacterial communities, while emphasizing the importance of host plant diversity in influencing the assembly of leaf bacterial communities.