Plant-associated microbes play a vital role in host health and evolution, but a fundamental understanding of their community dynamics through space and time is lacking. This gap in the knowledge hinders our ability to predict how plant microbiota will shift in response to climatic changes and perform in applied settings. We addressed this deficiency by examining how microbial communities change spatially and temporally in both the phyllosphere and rhizosphere. Specifically, we sought to determine (i) the dynamics of aboveground fungal communities over an entire growing season, (ii) how microbial communities are spatially structured across a gradient that varies sharply in abiotic conditions, and (iii) how belowground microbial communities respond to nitrogen deposition. Utilizing culture-independent techniques, we first examined the temporal turnover of fungal microbiota by sampling a population of plant hosts monthly for an entire growing season. We then assessed the community composition of microfungi in the same host species across four unique ecological habitats spanning 250 km. Finally, we extended our focus to grass-associated rhizospheric bacteria and monitored their temporal dynamics and variation across six common-garden sites spanning a climatic gradient, examining their shift in community composition in response to nitrogen addition across this temporal and spatial range.
Results/Conclusions
An examination of foliar fungi over an entire growing season reveals that colonization of newly-emerged plant tissue is patchy with heterogeneous communities between hosts. As a result, greater richness is found early in the season, yet priority effects are unable to counteract significant temporal turnover that occurs within the first three months. On a larger spatial scale, we find that plants host highly localized microbial communities, which is likely an effect of the functional redundancy of unique taxa at each site. Additionally, we find a subtle overlap of taxa in sites closer in proximity with little overlap in distant sites. Finally, when examining the response of microbes to nutrient addition, we find that temporal turnover plays a greater role in structuring microbial communities than nitrogen addition, but that geographic site has the highest influence on community composition. These results provide evidence that microbial communities are highly dynamic and that naturally-occurring temporal changes can exceed changes that result from anthropogenic perturbations. Since microbial communities can differ drastically between two time points or locations, it will be critical in future studies to report shifts in plant microbiota as occurring to a greater or lesser extent than their natural temporal and spatial variation.