Abstract
Temperature is an important factor governing microbe-mediated carbon feedback from permafrost soils. The link between taxonomic and functional microbial responses to temperature change remains elusive due to the lack of studies assessing both aspects of microbial ecology. Our previous study reported microbial metabolic and trophic shifts in response to short-term temperature increases in Arctic peat soil, and linked these shifts to higher CH4 and CO2 production rates (Proceedings of the National Academy of Sciences of the United States of America, 112, E2507-E2516). Here, we studied the taxonomic composition and functional potential of samples from the same experiment. We see that along a high-resolution temperature gradient (1-30°C), microbial communities change discretely, but not continuously or stochastically, in response to rising temperatures. The taxonomic variability may thus in part reflect the varied temperature responses of individual taxa and the competition between these taxa for resources. These taxonomic responses contrast the stable functional potential (metagenomic-based) across all temperatures or the previously observed metabolic or trophic shifts at key temperatures. Furthermore, with rising temperatures we observed a progressive decrease in species diversity (Shannon Index) and increased dispersion of greenhouse gas (GHG) production rates. We conclude that the taxonomic variation is decoupled from both the functional potential of the community and the previously observed temperature-dependent changes in microbial function. However, the reduced diversity at higher temperatures might help explain the higher variability in GHG production at higher temperatures.
Highlights
Northern permafrost soils represent the largest terrestrial organic carbon pool, and a major fraction of this carbon is stored in the near surface that is vulnerable to warming (Hugelius et al, 2014)
We have used DNA extracted from experiment samples harvested for the 2015 study (Tveit et al, 2015) to sequence 16S rRNA genes and mcrA genes. Combining this new data with reanalyses of metagenomes, metatranscriptomes and methane and CO2 accumulation data from the 2015 study, we have shown that temperature-driven shifts in the DNA-based microbial community composition are uncoupled from the functional potential of the community
The follow-up study presented here utilizes samples from the same experiment to demonstrate how broader, nonrandom, taxonomic responses to rising temperatures are not linked to the functional potential or any of the previously observed functional shifts
Summary
Northern permafrost soils represent the largest terrestrial organic carbon pool, and a major fraction of this carbon is stored in the near surface (the upper 3 m) that is vulnerable to warming (Hugelius et al, 2014). Disproportionate near-surface warming has made permafrost soil carbon increasingly vulnerable to decomposition into carbon dioxide (CO2) and methane. An important concern is whether such microbial feedbacks can in turn accelerate climate change (Mackelprang et al, 2011; Prater et al, 2007; Schuur et al, 2015). The response of microbial communities in arctic soils to global warming has important implications for the permafrost carbon feedback. The critical question centers on how microbial communities will respond to warming and how taxonomic and functional changes can influence GHG emissions. This key information is necessary to predict future carbon fluxes in permafrost soils (Graham et al, 2012)
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