Rain is composed of a diverse microbial community that may originate from near or distant sources. These microbes may be an important source for the leaf (phyllosphere) microbiome of terrestrial plants, but the extent rain microbes colonize terrestrial plants and contribute to variation in composition is unknown. We aimed to determine if rain communities are sources of phyllosphere microbes by asking 1) Does rainfall pattern influence the composition and abundance of rain microbial communities? 2) How do microbial colonizers from rain influence terrestrial phyllospheres? To address (1), we characterized the rain microbial community of August 2015–February 2016 (12 dates) using barcoding genes and measured the abundance of fungi in rain using microscopy. We addressed question (2) by testing the ability of rain microbes to colonize the phyllosphere by inoculating switchgrass seedlings with a mock rain fungal community at a concentration equivalent to rain. Next, we tested the overlap between rain and phyllosphere microbial communities by comparing the community from rain samples described above to phyllosphere metagenomes of switchgrass and miscanthus collected May 2016–September 2016 (n=136 across nine dates) from the KBS in southwest Michigan. Finally, we characterized the effect of rain extremity on the composition of phyllosphere microbes.
Results/Conclusions
Rain microbes colonized the phyllosphere and both rain and phyllosphere communities shifted with increase extremity of rain. Large rain events tended to correlate with reduced rain fungal abundance and reduced fungal:bacterial of reads though the correlations were non-significant (P > 0.3). Concentration of fungal colonists has a large effect on colonization rate because though our mock rain fungal community was able to colonize 31% of the switchgrass seedlings, the same strains were able to colonize 63% of the seedlings when inoculated at a higher concentration. Further supporting the negative effect of rain event size on colonization, fungal:bacterial of reads in the phyllosphere decreased with greater precipitation in the days preceding leaf sampling (P < 0.0001). We also found that though the rain and phyllosphere datasets were from two different years, the composition of reads matching rain fungi in the phyllosphere reached the highest relative abundance August to November (1% to 7% of the fungal reads) corresponding to the portion of the growing season in which rain was collected. Current work involves paired sampling of the rain and phyllosphere communities to examine whether shifts in rain amount and community composition correlates with the phyllosphere microbial community.