Everything is “not” everywhere, but the environment “still” selects

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Sarah Piché-Choquette, Vojtěch Tláskal and Petr Baldrian, Laboratory of Environmental Microbiology, Institute of Microbiology of the Czech Academy of Sciences, Prague, Czech Republic

Background/Question/Methods
Covering 30% of the Earth’s surface, forests represent the largest terrestrial ecosystem on Earth. They represent a highly heterogenous niche hosting organisms from all domains of life. Environmental heterogeneity is an important factor governing the distribution of species within and across ecosystems. To understand and maintain the integrity of natural landscapes, ecologists have documented the distribution of species across ecosystems and time scales using explanatory variables comprised within niche or neutral processes. Here, we aimed to determine which of these processes could best predict the heterogeneity of microbial communities in the temperate primeval forest Zofínský prales by performing an extensive systematic sampling at a scale of 10m to 80m. First, we quantified the importance of niche processes, as environmental filters, and neutral processes, as spatial patterns, in shaping microbial diversity and community structure within and across microhabitats. Second, we evaluated the niche overlap between microhabitats, expecting that most microbial species would be found everywhere, albeit in varying proportions. Seven terrestrial microhabitats were selected, including soil, twigs, branches, tree trunks, litter, senescent leaves, and roots (N=357). Microbial diversity and community composition were assessed using a metabarcoding survey of highly conserved genes in Fungi and Bacteria.
Results/Conclusions
Preliminary analyses of the fungal data showed that most microhabitats were clearly separated on the distance-based redundancy analysis ordination, while some had a much higher within-microhabitat homogeneity than others. The distribution of fungal “species” (amplicon sequence variants) was also distinct between microhabitats when clustered into ecophysiological guilds. Additionally, within-microhabitat spatial patterns, as assessed using Moran’s eigenvector maps, were significant drivers of microbial community composition, but in fewer than half of the microhabitats (3/7) and to a lower extent than expected (6.6% or less). Niche processes were better predictors of fungal community composition, especially between microhabitats, where the combination of carbon content, nitrogen content, pH, tree species and gravimetric water content could explain 35.03% of the total variance. Furthermore, the vast majority of “species” were not found in all nor most microhabitats, in spite of the small size of the sampled area. Taken together, those results show that despite the low limitation of dispersal at such a fine scale, forest microhabitats harbor distinct microbial communities, and the homogeneity of their community composition seems linked to the homogeneity of some of their abiotic features.