Abstract
Permafrost-underlain tundra soils in Northern Hemisphere are one of the largest reservoirs of terrestrial carbon, which are highly sensitive to microbial decomposition due to climate warming. However, knowledge about the taxonomy and functions of microbiome residing in different horizons of permafrost-underlain tundra soils is still limited. Here we compared the taxonomic and functional composition of microbiome between different horizons of soil cores from a moist tussock tundra ecosystem in Council, Alaska, using 16S rRNA gene and shotgun metagenomic sequencing. The composition, diversity, and functions of microbiome varied significantly between soil horizons, with top soil horizon harboring more diverse communities than sub-soil horizons. The vertical gradient in soil physico-chemical parameters were strongly associated with composition of microbial communities across permafrost soil horizons; however, a large fraction of the variation in microbial communities remained unexplained. The genes associated with carbon mineralization were more abundant in top soil horizon, while genes involved in acetogenesis, fermentation, methane metabolism (methanogenesis and methanotrophy), and N cycling were dominant in sub-soil horizons. The results of phylogenetic null modeling analysis showed that stochastic processes strongly influenced the composition of the microbiome in different soil horizons, except the bacterial community composition in top soil horizon, which was largely governed by homogeneous selection. Our study expands the knowledge on the structure and functional potential of microbiome associated with different horizons of permafrost soil, which could be useful in understanding the effects of environmental change on microbial responses in tundra ecosystems.
Highlights
About a quarter of the Northern Hemisphere terrestrial ecosystems are covered by permafrostunderlain soils (Zhang et al, 2008), which are key components in the global carbon cycle (McGuire et al, 2009), and stored approximately 50% (~1,700 Pg) of the global below-ground soil organic carbon (Tarnocai et al, 2009)
As soil microbiome plays a crucial role in decomposition and mineralization of organic matter in terrestrial ecosystems, it is important to have a better understanding of permafrost soil microbial ecology in order to improve our prediction of the potential consequences of climate warming on permafrost ecosystem function
Electrical conductivity, Water content (WC), Total carbon (TC), total nitrogen (TN), carbon-to-nitrogen ratio (C:N), NO3−-N, water extractable carbon (WEC) and WEN content were highest in top soil horizon (Oi) (Supplementary Table S1), whereas pH and NH4+-N, WEC-to-TC (WEC:TC) and WEN-to-TN (WEN:TN) ratios were highest in sub-soil horizons (Supplementary Table S1)
Summary
About a quarter of the Northern Hemisphere terrestrial ecosystems are covered by permafrostunderlain soils (Zhang et al, 2008), which are key components in the global carbon cycle (McGuire et al, 2009), and stored approximately 50% (~1,700 Pg) of the global below-ground soil organic carbon (Tarnocai et al, 2009). There has been increasing interest in understanding the diversity and functional potential of microbiome residing in permafrost soils (Yergeau et al, 2010; Mackelprang et al, 2011; Gittel et al, 2014a; Deng et al, 2015; Woodcroft et al, 2018; Tripathi et al, 2018a). The taxonomy and functional potential of microbiomes associated with different horizons of permafrost soils are still relatively poorly understood
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