Soil organic matter composition, transformation, and microbial colonisation of Gelic Podzols in the coastal region of East Antarctica

Abstract

During recent soil geographical expeditions to Casey Station (Coastal Antarctica), soils with the morphological features of Gelic Podzols (WRB: Spodic Haplic Cryosols) were found to be widespread. The purpose of this paper is to provide further information on these unique soils with respect to soil organic matter (SOM), microbiology, and soil formation. Antarctic Podzols develop on solid rock, outwash sediments, and abandoned penguin rookeries. A comparison of different SOM depth profiles, however, revealed carbon (C) and nitrogen (N) of unknown origin. The SOM composition was characterised by a mean C/N ratio of 10, with a high content of carboxyl-C units, probably derived from amino acids, organic acids, and oxidised carbohydrates. Pyrolysis-GC/MS and NMR showed a notable variation between SOM in depth profiles and the horizons within each profile. Microbial colonisation was affected by the surface vegetation, content of organic C, and the influence of seabirds. Correlations between selected SOM compounds and bacteria on the vegetated soils suggested that algal and moss C influence SOM to a great extent. Most of the long-chain C moieties in the antarctic Podzols appeared to contain multiple oxygen- and N-containing functional groups, cyclic ionised and heterocyclic structures, and alkylations. Data suggest that, along with the podzolisation process, organic acids, non-humified carbohydrates, and N-containing moieties migrated from the topsoil into the spodic horizons. The results are discussed with respect to (i) soil formation and (ii) microbial colonisation in the cold climate. The Gelic Podzols hold huge amounts of C and N but their origin is poorly understood. Explaining the origin of the SOM should be a focus for future research in antarctic soil biogeochemistry.