Permafrost as a source of mineral weathering bacteria: Implications of active layer thickening on James Ross Island, Antarctica

Abstract

Studying permafrost in Antarctica provides insights into climate history, soil and rock structure, and a unique biodiversity with potential impact on ecosystems. Although a great deal of effort has been devoted to the microbiological composition of permafrost soils, the objective pursued in this study is, for the first time, to examine soil and rock samples collected from a 350 cm deep core drilled near the Johann Gregor Mendel Czech Antarctic Station on the Ulu Peninsula of James Ross Island, to study the effect of geochemical properties on microbial composition and diversity and vice versa. We collected samples from the profile starting on the ground surface down to 350 cm depth and correlated information from metagenomic 16S rRNA gene analysis and geochemical data. The 80-cm-thick active layer had a distinct bacterial composition different from the Pseudomonadota-rich permafrost layer, with Actinomycetota, Acidobacteriota, Chloroflexota, and Verrucomicrobiota being the prevalent phyla. Throughout the core, the higher bacterial diversity was positively associated with the sand fraction and intensive weathering. The highest identified diversity in the deepest part of the active layer (transient active layer) suggests that the bacteria here have been gradually cryopreserved, possibly accumulating from the upper layers. In summary, the identified interface between the active layer and permafrost, as well as the transition within the permafrost from Holocene marine sediments to underlying Cretaceous sedimentary rocks (deeper than ∼ 260 cm), had the greatest influence on the bacterial composition. Decadal records of soil temperature and active layer thickness predict more significant interactions in the future between bacterial communities in the current active layer and mineral weathering bacteria that are typical of permafrost.