Soil bacterial community and functional shifts in response to altered snowpack in moist acidic tundra of northern Alaska

Abstract

Abstract. Soil microbial communities play a central role in the cycling of carbon (C) in Arctic tundra ecosystems, which contain a large portion of the global C pool. Climate change predictions for Arctic regions include increased temperature and precipitation (i.e. more snow), resulting in increased winter soil insulation, increased soil temperature and moisture, and shifting plant community composition. We utilized an 18-year snow fence study site designed to examine the effects of increased winter precipitation on Arctic tundra soil bacterial communities within the context of expected ecosystem response to climate change. Soil was collected from three preestablished treatment zones representing varying degrees of snow accumulation, where deep snow ∼ 100 % and intermediate snow ∼ 50 % increased snowpack relative to the control, and low snow ∼ 25 % decreased snowpack relative to the control. Soil physical properties (temperature, moisture, active layer thaw depth) were measured, and samples were analysed for C concentration, nitrogen (N) concentration, and pH. Soil microbial community DNA was extracted and the 16S rRNA gene was sequenced to reveal phylogenetic community differences between samples and determine how soil bacterial communities might respond (structurally and functionally) to changes in winter precipitation and soil chemistry. We analysed relative abundance changes of the six most abundant phyla (ranging from 82 to 96 % of total detected phyla per sample) and found four (Acidobacteria, Actinobacteria, Verrucomicrobia, and Chloroflexi) responded to deepened snow. All six phyla correlated with at least one of the soil chemical properties (% C, % N, C : N, pH); however, a single predictor was not identified, suggesting that each bacterial phylum responds differently to soil characteristics. Overall, bacterial community structure (beta diversity) was found to be associated with snow accumulation treatment and all soil chemical properties. Bacterial functional potential was inferred using ancestral state reconstruction to approximate functional gene abundance, revealing a decreased abundance of genes required for soil organic matter (SOM) decomposition in the organic layers of the deep snow accumulation zones. These results suggest that predicted climate change scenarios may result in altered soil bacterial community structure and function, and indicate a reduction in decomposition potential, alleviated temperature limitations on extracellular enzymatic efficiency, or both. The fate of stored C in Arctic soils ultimately depends on the balance between these mechanisms.

Deeper snow increases the net soil organic carbon accrual rate in moist acidic tussock tundra:210Pb evidence from Arctic Alaska

“…However, abiotic and biotic interactions may change the magnitude, extent, redistribution, and even longerterm net effect of this increased soil carbon sink. For instance, thawing of previously frozen soils may initially stimulate rates of microbial degradation of organic carbon, and as accessible carbon pools are depleted over time and soil conditions change, microbial communities may shift toward more effective decomposition and metabolic strategies (Ricketts et al 2016;Melillo et al 2017). Competing rates of soil methanogenesis versus respiration, which respectively emit CH 4 and CO 2 to the atmosphere, depend in large part on whether the soils are wet or dry (Blanc-Betes et al 2016).…”

“…Increases and decreases in snowfall and winter snowpack can lead to different ecosystem impacts (Bintanja and Selten 2014;Bintanja and Andry 2017). The effects of these changes on soil organic carbon inventories depend on soil carbon cycling processes (Schaeffer et al 2013;Ricketts et al 2016;Vitharana et al 2017) and soil active layer depth (Pattison and Welker 2014;Jespersen et al 2018). Improved understanding of the mechanisms driving the arctic carbon cycle continues to be at the forefront of research on the role of the "New Arctic" in the global climate system, especially processes that drive winter carbon emissions (Fahnestock et al 1999;Lupascu et al 2018;Natali et al 2019).…”

Mimicking climate warming effects on Alaskan soil microbial communities via gradual temperature increase

“…Only phyla with a relative abundance higher than 1% are displayed. (2020) 10:8533 | https://doi.org/10.1038/s41598-020-65329-x www.nature.com/scientificreports www.nature.com/scientificreports/ coverage 35 . Higher elevations receive higher amounts of snow and the snow melts later in the year.…”

“…Higher elevations receive higher amounts of snow and the snow melts later in the year. The increased abundance can thus be decoupled from elevation and is probably a result of reduced oxygen availability and increased soil temperatures underneath an increased snowpack 35 .…”

Evidence of Ash Tree (Fraxinus spp.) Specific Associations with Soil Bacterial Community Structure and Functional Capacity

“…Sequences were rarefied at 5900 sequences per sample for diversity analysis. More detailed methods can be found in Ricketts et al, 2016 [25].…”