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In Arctic soils, warming accelerates decomposition of organic matter and increases emission of greenhouse gases (GHGs), contributing to a positive feedback to climate change. Although microorganisms play a key role in the processes between decomposition of organic matter and GHGs emission, the effects of warming on temporal responses of microbial activity are still elusive. In this study, treatments of warming and precipitation were conducted from 2012 to 2018 in Cambridge Bay, Canada. Soils of organic and mineral layers were collected monthly from June to September in 2018 and analyzed for extracellular enzyme activities and bacterial community structures. The activity of hydrolases was the highest in June and decreased thereafter over summer in both organic and mineral layers. Bacterial community structures changed gradually over summer, and the responses were distinct depending on soil layers and environmental factors; water content and soil temperature affected the shift of bacterial community structures in both layers, whereas bacterial abundance, dissolved organic carbon, and inorganic nitrogen did so in the organic layer only. The activity of hydrolases and bacterial community structures did not differ significantly among treatments but among months. Our results demonstrate that temporal variations may control extracellular enzyme activities and microbial community structure rather than the small effect of warming over a long period in high Arctic soil. Although the effects of the treatments on microbial activity were minor, our study provides insight that microbial activity may increase due to an increase in carbon availability, if the growing season is prolonged in the Arctic. [ABSTRACT FROM AUTHOR]

Global climate change models predict that surface temperature and precipitation will increase in the Polar Regions. Arctic tundra soils contain a large amount of carbon, which may be vulnerable to decomposition under potential climate change. However, mechanistic understanding of the decomposition process and the consequent changes remains lacking. In the present study, we conducted a manipulation experiment at an arctic soil system in Cambridge Bay, Canada, where temperature and precipitation were increased artificially by installing open top chambers and adding distilled water during growing seasons. After one and half year of environmental manipulation, we investigated extracellular enzyme activities, which are related to decomposition, and analyzed stable isotope signatures (δ 13 C and δ 15 N) in soils and plants, which are related to water and nitrogen availability. Hydrolase (β- d -glucosidase, cellobiase, N-acetyl-glucosidase and aminopeptidase) activity did not differ significantly under different treatments. However, phenol-oxidase showed higher activity under warming combined with increased precipitation than under other treatments. Stable isotope ratio (δ 13 C) in plants revealed that drought stress in vegetation was induced under warming. We concluded that in the long term, climate change may amplify the feedback of soil to climate change in arctic tundra soil. [ABSTRACT FROM AUTHOR]