Scaling of phyllosphere epiphyllous bacterial diversity with tree size across temperate forests

Phyllosphere bacteria form a part of the extended phenotype of host plants, and can strongly influence plant environmental adaptability. However, little is known about whether and how phyllosphere bacterial diversity covaries with tree size, and how these relationships vary across environmental gradients. In this study, we collected 210 leaf samples from seven dominant and common tree species across five natural temperate forests throughout Northeast China. We measured leaf economic spectrum traits, the diameter at breast height, and phyllosphere epiphyllous bacterial communities of each tree. Our results showed that diameter at breast height was positively associated with phyllosphere epiphyllous bacterial richness. The influence of homogeneous selection on community assembly declined with increasing tree size and was closely linked to more conservative leaf economic spectrum traits. Latitudinal variation in mean annual temperature further modulated these relationships, with lower mean annual temperature strengthening the coupling between tree size and phyllosphere epiphyllous bacterial diversity. Our study extends the understanding of tree size-trait relationships by incorporating the perspective of the phyllosphere microorganisms. We conclude that both leaf functional traits and phyllosphere community traits should be considered when evaluating the ecological and evolutionary constraints on tree life history trade-offs.