Abstract
In this study, we determine differences in total biomass of soil microorganisms and community structure (using the most probable number of bacteria (MPN) and the number of fungal genera) in patterned ground features (PGF) and adjacent vegetated soils (AVS) in mesic sites from three High Arctic islands in order to characterize microbial dynamics as affected by cryoturbation, and a broad bioclimatic gradient. We also characterize total biomass of soil microorganisms and the most probable number of bacteria along a topographic gradient within each bioclimatic subzone to evaluate whether differences in topography lead to differences in microbial dynamics at a smaller scale. We found total microbial biomass C, the most probable number of heterotrophic bacteria, and fungal genera vary along this bioclimatic gradient. Microbial biomass C decreased with increasing latitude. Overall, microbial biomass C, MPN and the number of fungal isolates were higher in AVS than in PGFs. The effects which topographic position had on microbial biomass C varied across the bioclimatic gradient as there was no effect of topographic position in Isachsen (subzone A) and Mould Bay (subzone B), when compared to Green Cabin (subzone C, warmer site).There was no effect of topographic position on MPN counts at Mould Bay and Green Cabin. However, in Isachsen, MPN counts were highest in the wet topographic position as compared to the mesic and dry. In conclusion, PGFs seem to decouple the effect climate that might have on the total biomass of soil microorganisms along the bioclimatic gradient; and influence gets ameliorated as latitude increases. Similarly, the effect of topography on the total microbial biomass is significant at the warmest bioclimatic zone of the gradient. Thus, climate and topographic effects on total microbial biomass increase with warmer climate.
Highlights
The Arctic, far from a homogenous biome in terms of ecosystem properties and processes, exhibits a great deal of ecological variation along gradients of climate, substrate, topography, and disturbance [1]
Microbial biomass C was significantly higher in adjacent vegetated soils (AVS) than in patterned ground features (PGF) at Mould Bay (F = 5.64, P = 0.02, R2 = 0.17), and Green Cabin (F = 51.93, P < 0.0001, R2 = 0.65) in the mesic topographic position
When we analyzed the data from all topographic positions and locations together within a study site, we found that microbial biomass C was significantly higher at AVS than in PGFs at Isachsen (P = 0.05, R2 = 0.46) and Green Cabin but not at Mould Bay (P = 0.30, R2 = 0.34)
Summary
The Arctic, far from a homogenous biome in terms of ecosystem properties and processes, exhibits a great deal of ecological variation along gradients of climate, substrate, topography, and disturbance [1]. The mosaic of vegetation and associated ecosystem properties and processes is controlled at a broad scale by soil chemistry, with strong differences between acidic and nonacidic parent material [4] and at a finer scale by topographic gradients controlling soil moisture, snow depth, exposure, and soil development [5]. Superimposed over these gradients is the pattern developed by the persistent disturbance of cryoturbation or soil churning due to soil water movement and frost heave, which creates patterned OPEN ACCESS OJSS. The center portion of the PGFs is often not vegetated (See Figure 1)—so contributing to the characteristic portrayal of High Arctic ecosystems as large areas of bare ground— yet, they are important to global C budgets because they contain a large reservoir of soil C [9] as organic materials from the adjacent vegetated areas get incorporated into the soil horizons within the PGF during the seasonal freeze-thaw cycles
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