Effects of long-term experimental warming on phyllosphere epiphytic bacterial and fungal communities of four alpine plants

The effects of climatic warming on phyllosphere microbial communities remain uncertain. In this study, the effects of long-term (>10 years) experimental warming on phyllosphere epiphytic bacterial and fungal communities of Carex alrofusca, Kobresia pygmaea, Potentilla bifurca and Stipa capillacea were examined in the Northern Tibet. Overall, warming increased bacterial α-diversity, but reduced fungal α-diversity across the four host plants. Warming altered the bacterial and fungal community compositions mainly by increasing Actinobacteria, Firmicutes and pathotroph-saprotroph fungi, and reducing Basidiomycota and symbiotroph fungi across the four host plants. Warming increased the relative effect of the 'drift & others' process in the bacterial community, but reduced the relative effect of the 'dispersal limitation' process in the bacterial community and the relative effect of the 'homogeneous selection' process in the fungal community across the four host plants. The overall warming effects on the bacterial and fungal communities may be due to overall warming effects on temperature, leaf morphology structure and physicochemical properties, ecological processes of community assembly and topological parameters of species co-occurrence networks of bacteria and fungi. Warming altered the bacterial species co-occurrence network mainly by increasing the vertex, clustering coefficient and heterogeneity, while reducing the average path length and network diameter across host species. Warming altered the fungal species co-occurrence network mainly by increasing the network diameter and reducing the vertex across host species. Warming effects on bacterial and fungal communities varied among host plants, which may be due to the diverse responses to warming of plant height, leaf malondialdehyde, ecological processes of community assembly and topological parameters of species co-occurrence network. Therefore, warming can alter phyllosphere epiphytic bacterial and fungal communities of alpine plants. Such changes varied among host plants and may cause adverse effects on the host plants.