Microbial diversity and community–environment relationships in boreal streams

Abstract

Aim The perspective that microbial communities are controlled solely by environmental factors (‘everything is everywhere, but the environment selects’) has persisted for a long time, notwithstanding that recent studies have found that both environmental factors and spatial processes are important. We examined variation in the structure of fungal and bacterial communities in boreal streams along large local environmental gradients (e.g. stream size, acidity and nutrients) at intermediate spatial extent. Owing to the intermediate spatial extent of our study area and high dispersal rates of microbes, we expected that local environmental factors would structure stream fungal and bacterial communities. Location A set of 30 streams was sampled along a geographical transect from western to eastern Finland. Methods Leaf packs were used as sampling units in each stream. Fungal and bacterial operational taxonomic units (OTUs) were determined using pyrosequencing in the laboratory. Species accumulation curves were used to assess how well the regional species pools were sampled. Partial redundancy analysis and partial linear regression were used to determine the relative contributions of environmental and spatial variables to community structure and OTU richness, respectively. Results We found that environmental control was important in structuring fungal and bacterial communities, yet much of the variation was attributable to the shared effects of environmental and spatial predictors, or remained unexplained. The composition of fungal and bacterial communities was most strongly related to water chemistry variables (i.e. pH, aluminium and total phosphorus), whereas habitat variables (i.e. riparian deciduous trees, moss cover, substratum particle size and stream width) were clearly less important. We also found that fungal richness was negatively related to water iron concentration, whereas bacterial richness showed only a weak relationship with water pH. Main conclusions The composition and richness of stream microbial communities are mostly related to water chemistry variables at the spatial extent studied, emphasizing an important role for species sorting. This finding supports the traditional perspective that local environmental conditions are important drivers of variation in microbial communities. However, much of the variation in fungal and bacterial communities remained unexplained, suggesting that drivers of these communities are likely to be complex and not yet fully understood.

Disentangling multi‐scale environmental effects on stream microbial communities

“…(), 15% explained variation in Heino et al . ()), is presumably partly related to the very large number of OTUs. The wide variation in the overall number of OTUs and different detecting and delineating methods among studies hinders their direct comparisons.…”

Environmental degradation results in contrasting changes in the assembly processes of stream bacterial and fungal communities

“…Our study adds to this knowledge showing that disturbance can lead to very different outcomes in different taxonomic groups that likely depend on differences in the sensitivities of species to disturbances and prevailing assembly mechanisms in the initial environmental conditions. Little is still known about how niche‐based and neutral processes assemble metacommunities of microorganisms in natural environmental settings (Soininen , Heino et al , Mueller et al ). A better understanding of the environmental tolerances of microbes and the mechanisms assembling microbial communities in natural environmental settings is needed to predict how environmental alteration is likely to affect microbial communities.…”

Biogeography of aquatic hyphomycetes: Current knowledge and future perspectives

“…Different molecular tools have been applied to assess streamdwelling decomposer fungal communities (DGGE: 5 streams in Northwestern Portugal, Duarte et al, 2009;5 streams in Northeastern France, Clivot et al, 2013;9 streams in South-central Sweden, Bergfur and Sundberg, 2014;clone libraries: 5 streams in Northeastern France, Clivot et al, 2013;and 454 pyrosequencing: 30 streams in North-western and -eastern Finland, Tolkkinen et al, 2013;Heino et al, 2014;5 streams in Northwestern Portugal, Duarte et al, 2015). In these studies, aquatic hyphomycete communities were structured by similar environmental drivers, regardless of whether they were evaluated by conidium identification or genetic diversity (e.g.…”

“…To disentangle the relative importance of local versus regional factors in structuring aquatic hyphomycete communities in world freshwaters, repeated, multi-scale sampling is crucial (Heino et al, 2014). In fact, the pyrosequencing of soil samples from 365 globally distributed sites allowed, for the first time, integrating fungi into a general macroecological framework (Tedersoo et al, 2014b).…”