Evaluation of the soil microbial diversity of three raised beaches in the Devon Plateau, Devon Island, Nunavut, Canada

The Arctic region, characterised by severe temperatures and a unique ecosystem, encompasses a peculiar microbiome in its soil. The soil microbiome has a crucial function in nutrient cycling, organic matter decomposition, greenhouse gas emissions, and the general functioning of the ecosystem. Increasing the knowledge about the composition, diversity, and dynamics characterising the Arctic soils' microbiome is fundamental to better understanding the ecological processes within this threatened evolving environment. In this study, we compared the microbial profiles of three raised beaches in Devon Island (Nunavut, CA) to explore their similarities and differences. Samples were collected from each investigated site named AB1, AB2, and AB3, performing a vertical sampling from the active layer to the permafrost. Soil microbial DNA was isolated from each sample for 16S rRNA gene multi-amplicon metabarcoding sequencing using the Ion GeneStudio S5 System. Afterwards, the sequencing data were analysed using the QIIME2 pipeline to identify and compare the core microbial profile. The quantification of total DNA revealed a consistently comparable quantity of genetic material across the three beaches (AB1 µ= 4.71±2.35 µg·g-1, AB2 µ= 2.28±5.44 µg·g-1, AB3 µ= 5.44±2.91 µg·g-1), irrespective of the age of the investigated area (AB1=6,726 YBP, AB2=2,360 YBP, AB3=8,410 YBP). Regarding the 16S metabarcoding data analysis, it is noteworthy that both alpha and beta diversity analyses showed a consistent absence of significant differences among the investigated areas that can be attributed to their common location within the Devon Plateau. This shared geographical setting exposes them to identical pedoclimatic conditions, which exert consistent ecological pressures on soil microbial communities. On the contrary, the horizon clustering underscores how the physicochemical distinctions observed among the investigated horizons actively contribute to defining the composition and structure of microbial communities. In particular, the hierarchical cluster analysis based on the Bray-Curtis dissimilarity matrix vividly illustrates the distinct separation between surface and deep horizons. Eventually, the core microbiome analysis highlights that Actinobacteriota, Proteobacteria, and Firmicutes are the top three predominant phyla accounting for relative abundances of 42%, 22%, and 18%, respectively. In conclusion, (i) total soil DNA is a relatively stable molecule that can be detected and analysed after a substantial amount of time has elapsed, (ii) the physicochemical characteristics soils exert a significant influence on the composition and clustering of microbial communities, and (iii) The analysis of the core microbiome demonstrates that, even in a cryoturbated environment, evolutionary convergence appears to favor the predominance of Actinobacteriota, Proteobacteria, and Firmicutes, bacterial phyla known to be dominant in environments subject to significant environmental disturbances, such as wildfires.