The bacterial and fungal community assemblages in the Eucalyptus phyllosphere are shaped by contrasting ecological processes.

Abstract

Plant performance and ecosystem functioning are inextricably tied to the phyllosphere microbiome. However, little is known about how ecological processes influence the biogeography of various phyllosphere microbial populations. Here, we examined the biogeographic patterns of fungal and bacterial communities in phyllosphere samples of plants from the Myrtaceae family's species Eucalyptus that were taken across a distance of more than 4000 km. We examined how the two main ecosystem processes—stochastic and deterministic—affect the assembly of microbial communities in the phyllosphere. Our findings showed that 64.2% of the fluctuations in bacterial community assembly, which had a normalised stochasticity ratio of 71.8%, were described by the neutral community model, which can measure the degree of a community assembly caused by stochastic processes. These findings imply that stochastic processes play a major role in influencing the formation of bacterial communities. On the other hand, a normalised stochasticity ratio of 25.1% and a comparatively low explanation rate of the neutral community model (48.7%) indicate that deterministic mechanisms dominated the formation of phyllosphere fungal communities. The findings of random forest modelling and variation partitioning analysis showed that both bacterial and fungal bio-geographic patterns in the phyllosphere were driven by climatic parameters, especially mean annual precipitation and aridity index. Fungal community assembly was more strongly correlated with edaphic variables than bacterial community assembly, such as soil organic and mineral nitrogen concentration. The distinct characteristics of bacteria and fungus, such as the greater potential dispersion rate and broader habitat niche of bacteria compared to fungi, may be responsible for the varied reactions of bacterial and fungal populations to environmental conditions.The "size plasticity" theory, which holds that smaller organisms (bacteria) are more homogeneous across space and less affected by environmental conditions than larger organisms (fungi), is supported by our findings, which showed that phyllosphere bacterial and fungal communities followed distinct community assembly processes. These results provide fresh perspectives on the microbial ecology of microbiomes in the phyllosphere of plants.