Environmental Context Mediates the Relationship between Leaf Traits and the Foliar Fungal Microbiome

Leaf traits impact the colonization and growth of microbes in and on leaves, and thereby influence the process of foliar microbiome assembly. However, most studies on this topic are conducted under controlled environmental conditions, limiting the understanding of the role of leaf trait plasticity for microbial community assembly outcomes. Uncovering how both leaf traits and microbes respond to environmental variation is critical to unlocking the relationship between plant genotype and phenotype relationships for the plant microbiome and ultimately to improve our ability to manage the microbiome in agriculture. We characterized leaf traits and used DNA metabarcoding to examine the fungal leaf microbiome in the model tree, Populus trichocarpa, planted in climatically contrasting reciprocal common gardens. We found that the relationship between leaf traits and P. trichocarpa foliar fungal diversity and community composition varied across environments. Stomatal length was more positively correlated with fungal diversity and composition in the mesic garden than in the xeric garden, with greater trait plasticity in genotypes originating from mesic environments contributing to this shift. Overall, our study highlights the necessity of integrating environmental variation into our understanding of how plant traits influence the microbiome.