Soil microbial diversity across a Greenlandic glacial chronosequence

Accelerated glacial retreat in Greenland drives increased development of glacial outwash plains. These newly exposed soils provide an opportunity to study microbial dynamics during soil development. We explore soil microbial diversity, community assembly, and biogeochemical cycling across the Kiattuut Sermiat glacial chronosequence (southern Greenland) via 16S rRNA gene amplicon analysis paired with microbial abundance, soil physicochemical parameters, and gas flux data. Microbial diversity varied with soil depth, with more acidic topsoils abundant in Cyanobacteriota and Armatimonadota taxa. While lower soils represented an oxygen transition zone, hosting aerobic nitrifiers such as Nitrospirota, low oxygen associated Planctomycetota taxa, and less characterised Gemmatimonadota. Microbial diversity varied across the chronosequence following distance-decay principles, as communities were predominately dispersal limited and shaped by heterogenous selection, with greater heterogeneous conditions in older soils. Soil CO2 fluxes (-0.02 to 0.83 µmol m-2 s-1) increased in more developed soils, following a shift from autotrophic sulfur- and iron-oxidising taxa towards heterotrophic members. CH4 fluxes (-0.84 to 0.15 nmol m-2 s-1) demonstrated greater uptake in older soils and CH4-oxidation was associated with the methanotroph Methylocapsa. Considering the climatic relevancy of Greenlandic proglacial environments, we describe the largely unexplored microbial diversity and biogeochemical cycling of greenhouse gases in these developing soils.