Increased carbon inputs alter soil microbial genetic potential for biogeochemical cycling in Arctic ecosystems

Global warming is transforming High Arctic ecosystems, yet the effects of northward vegetation expansion on soil microbial functions remain unclear. A four-year field experiment in northern Greenland was conducted to study these impacts. We investigate how plant litter affects the active layer and thawing permafrost soils by transplanting the latter from deeper soil layers and supplementing active layer soils with Arctic shrub litter. Litter amendment altered the soils’ functional potential, including the enrichment of genes linked to ion and lipid transport, metabolism and secondary metabolite production, ultimately enhancing microbial growth and respiration. Significant alterations were observed in carbon (C) and nitrogen (N) cycling genes, marked by an enhancement of CAZymes related to the breakdown of specific C substrates such as cellulose, hemicellulose, pectin, murein and chitin. Litter amendment also shifted the microbial N-cycling potential towards increased N mineralization and assimilation of organic and inorganic N, suggesting an increased incorporation of N into microbial biomass. Without litter amendment, few C- and N-metabolism pathways changed, mainly affecting auxiliary activities and lignin breakdown due to permafrost thawing. These findings highlight the importance of monitoring High Arctic vegetation expansion, as it may impact C degradation and greenhouse gas emissions more than permafrost thaw alone.