Abstract
Ongoing climate change involves increasing snow scarcity, which results in more frequent freeze-thaw cycles (FTCs) in polar and alpine soils. Although repeated FTCs have been shown to alter the structure and functions of soil microbial communities, a thorough understanding on the influence of FTCs frequency on polar and especially alpine soil microbiomes is still elusive. Here, we investigated the impact of repeated weekly vs. daily FTC frequencies on the structure and functions of prokaryotic and fungal communities from north- and south-exposed soils from two mountain ridges, one in the Arctic and one in the High-Alps. FTCs affected prokaryotic communities more strongly than fungal communities, where mainly cold-tolerant and opportunistic fungi (e.g., Mrakia, Mortierella) were responsive. Prokaryotic communities were more affected by weekly FTCs than by daily FTCs. Daily FTCs favored fast-growing bacteria (e.g., Arthrobacter), while oligotrophic and largely uncultured taxa (e.g., Verrucomicrobia) benefited from weekly FTCs. FTCs negatively affected microbial respiration but had minor impacts on C-, N- and P-acquiring enzymatic activities. Plausible pre-adaptation of the microbial communities to naturally occurring frequent FTCs at their site of origin did not show a clear influence on the microbial responses to the tested FTCs. Altogether, our study provides an integrative overview on potential structural and functional changes of soil microbial communities in polar and alpine regions in response to the projected increase in FTCs; therefore advancing our understanding on the impact of climate change in these rapidly changing ecosystems.
Highlights
Climate change scenarios predict an increase in air temperatures worldwide of up to 3.7◦C by 2100, along with greater variation in air temperature and precipitation (IPCC, 2014)
By comparing the highly frequent daily freezethaw cycles (FTCs) with the infrequent weekly FTCs and including compositional and functional data, we provide an integrative overview of potential dynamic responses that arctic and alpine soil microbiomes might undergo in the future, as snow becomes scarce and FTCs become more frequent
Our integrative investigation of the impact of FTC frequency on the structure and functionality of microbial communities of arctic and alpine soils suggested a trait-based response of prokaryotic communities to FTC frequency, where repeated short and frequent FTCs seemed to benefit copiotrophic bacteria while longer and less frequent FTCs seemed to promote oligotrophic bacteria
Summary
Climate change scenarios predict an increase in air temperatures worldwide of up to 3.7◦C by 2100, along with greater variation in air temperature and precipitation (IPCC, 2014). These climatological changes might have important consequences on soil ecosystems, where fluctuations in soil temperatures and moisture might alter microbial diversity (Balser et al, 2010), microbially mediated ecological functions (Steinweg et al, 2013; Karhu et al, 2014) and, the. Soil temperature oscillations around 0◦C cause freezethaw cycles (FTCs), which are common in polar and alpine regions, especially during late fall and early spring when the absence of snow means a closer coupling between air and soil temperatures (Henry, 2013). Snow-free soils, on the contrary, respond to hourly air temperature variations and undergo daily FTCs when night temperatures fall below 0◦C (Freppaz et al, 2007)
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