Vegetation-Associated Impacts on Arctic Tundra Bacterial and Microeukaryotic Communities

Abstract

The Arctic is experiencing rapid vegetation changes, such as shrub and tree line expansion, due to climate warming, as well as increased wetland variability due to hydrological changes associated with permafrost thawing. These changes are of global concern because changes in vegetation may increase tundra soil biogeochemical processes that would significantly enhance atmospheric CO 2 concentrations. Predicting the latter will at least partly depend on knowing the structure, functional activities, and distributions of soil microbes among the vegetation types across Arctic landscapes. Here we investigated the bacterial and microeukaryotic community structures in soils from the four principal low Arctic tundra vegetation types: wet sedge, birch hummock, tall birch, and dry heath. Sequencing of rRNA gene fragments indicated that the wet sedge and tall birch communities differed significantly from each other and from those associated with the other two dominant vegetation types. Distinct microbial communities were associated with soil pH, ammonium concentration, carbon/nitrogen (C/N) ratio, and moisture content. In soils with similar moisture contents and pHs (excluding wet sedge), bacterial, fungal, and total eukaryotic communities were correlated with the ammonium concentration, dissolved organic nitrogen (DON) content, and C/N ratio. Operational taxonomic unit (OTU) richness, Faith's phylogenetic diversity, and the Shannon species-level index (H=) were generally lower in the tall birch soil than in soil from the other vegetation types, with pH being strongly correlated with bacterial richness and Faith's phylogenetic diversity. Together, these results suggest that Arctic soil feedback responses to climate change will be vegetation specific not just because of distinctive substrates and environmental characteristics but also, potentially, because of inherent differences in microbial community structure.T he rate of increase in Arctic surface air temperatures has been twice as rapid as the average global rate (ϳ0.10°C per decade) (1, 2) over the last few decades (3); this augmented warming has impacted Arctic species and ecosystems (4). Arctic shrub cover and density have increased, the tree line has migrated in some places, and the distribution of wetland vegetation is changing in association with permafrost thawing (5, 6). Because plants supply organic matter to soils and impact belowground soil microbial communities (7,8), changes in soil vegetation cover could result in substantial bacterial, fungal, and metazoan community composition changes (9-12). These changes could alter overall biogeochemical functioning, such as the release of carbon via soil decomposition, in these ecosystems (13), which would be expected to further exacerbate climate change. A better understanding of the vegetation-associated soil microbial structures could facilitate predictions of the effects of climate change on tundra ecosystems and determine if Arctic soil feedback responses to climate change are vegetation specific.Bacterial conso...

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