Abstract
Salinity is a major driver of bacterial community composition across the globe. Despite growing recognition that different bacterial species are present or active at different salinities, the mechanisms by which salinity structures community composition remain unclear. We tested the hypothesis that these patterns reflect ecological coherence in the salinity preferences of phylogenetic groups using a reciprocal transplant experiment of fresh- and saltwater wetland soils. The salinity of both the origin and host environments affected community composition (16S rRNA gene sequences) and activity (CO2 and CH4 production, and extracellular enzyme activity). These changes in community composition and activity rates were strongly correlated, which suggests the effect of environment on function could be mediated, at least in part, by microbial community composition. Based on their distribution across treatments, each phylotype was categorized as having a salinity preference (freshwater, saltwater, or none) and phylogenetic analyses revealed a significant influence of evolutionary history on these groupings. This finding was corroborated by examining the salinity preferences of high-level taxonomic groups. For instance, we found that the majority of α- and γ-proteobacteria in these wetland soils preferred saltwater, while many β-proteobacteria prefer freshwater. Overall, our results indicate the effect of salinity on bacterial community composition results from phylogenetically-clustered salinity preferences.
Highlights
Understanding if and how the evolutionary history of a species relates to its ecology is a fundamental question for biologists
A strong negative relationship was found between the abundance of methanogens and δ-proteobacterial sulfate-reducing bacteria (SRB) (r = −0.79, p < 0.01)
We investigated the effects of salinity on wetland microbial community composition and activity via an in situ salinity manipulation experiment, and assessed whether phylogenetic clades of bacteria exhibited ecological coherence with regard to their salinity preferences
Summary
Understanding if and how the evolutionary history of a species relates to its ecology is a fundamental question for biologists. Phylogeny is often an ecologically meaningful way to classify organisms, as closely related taxa frequently have similar ecological characteristics (e.g., Silvertown et al, 2006; Donoghue, 2008) and functional traits (e.g., CavenderBares et al, 2009). Most research into the ecology of microorganisms has relied on phylogenetic classification, and there is an accumulating body of evidence that shows phylogenetically-clustered taxa exhibit a substantial degree of ecological similarity, even at high levels of taxonomic organization (Philippot et al, 2010; Langille et al, 2013). Phylogenetically-clustered salinity preferences or traits that distinguish them from other clades (Philippot et al, 2010)] has been demonstrated for the orders of α-proteobacteria, where members of each order are similar in multiple regards including habitat preference and genome size (Ettema and Andersson, 2009). An increased understanding of these relationships could lead to a more predictive understanding of how environmental variables shape bacterial community composition and could help explain global patterns in bacterial biodiversity
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