The Effect of Environmental Perturbations on the Plant Phyllosphere Microbiome

Applying ecological concepts to microbial communities has proved to be challenging, often revolving around the relative importance of stochastic and deterministic processes applied heterogeneously across the habitat in time or space. The phyllosphere is the aboveground surface of plants on which microbial communities, composed primarily of Bacteria, but also including Archaea and microbial eukaryotes, exist and is characterized by stochastic immigration balanced with strong selective forces. Variation in bacterial community composition was characterized across space and time, with special attention given to the exposure of phyllosphere communities to rain as a plausible mechanism of ecological disturbance. Bacterial communities were characterized through targeted Illumina sequencing of the 16S rRNA taxonomic marker gene. Biogeographic patterns of bacteria in the phyllosphere were found to be evident from southern magnolia (Magnolia grandiflora) trees 1-452 m apart in a small forest plot. A significant relationship between canopy cover and tree elevation and differences in bacterial abundances but not in bacterial incidence, suggesting that bacterial abundance and incidence in the phyllosphere is shaped by different assembly mechanisms. More broadly, this suggests that environmental parameters and neutral forces may influence spatial patterns in the phyllosphere, even at small spatial scales. Separately, the effects of rain were investigated in both short-term and long-term contexts. First, rain as a short-term disturbance was contrasted against long-term seasonal changes to the phyllosphere bacterial community of broadleaf cattail (Typha latifolia) plants collected across an entire year, specifically targeting days before rain events and up to five days after. Secondly, the effect of rain throughout the tree canopy of M. grandiflora was investigated. Across both studies, rain did not appear to have any effect on bacterial community richness, evenness, novel species accumulation, or composition. Instead, longer seasonal trends determined diversity and compositional patterns in T. latifolia, while canopy structure had the strongest influence on M. grandiflora. These findings suggest that rain does not act as an ecological disturbance towards the phyllosphere bacterial community and that short-term abiotic disruptions may exert minimal influence on its composition and development in comparison to longer trends or spatial heterogeneity which likely influence the plant host as well