Soil Organic Matter Mineralization and Transformation in Inner Shelf Oases of East Antarctica: Laboratory Assessments and Role of Environmental Drivers

Soils of ice-free regions (oases) in East Antarctica have been rarely investigated via the prism of combined detailed biological and chemical methods. The main purpose of this work is to assess the influence of environmental factors, including microrelief and local features of the accumulation of biogenic material on the mineralization and humification of the organic matter in topsoils from Bunger Hills and Schirmacher Oasis. We used multiple techniques to analyze soil basal respiration and mineralization rates, extract humic acids, and investigate their molecular structure by ¹³C-NMR spectroscopy. The results reveal that soil formed under moss cushions exhibits the highest levels of organic carbon (up to 2.43%), alongside elevated basal respiration rates, which reached up to 2.979±0.015 mg g −1 day −1 in moist conditions. Soil pH ranged from slightly acidic to alkaline, influenced by salt accumulation, which adversely affects plant communities and limits biomass production. Using 13 C-NMR spectroscopy, although in a limited number of samples, we identified a predominance of aliphatic structures in humic acids with carboxylic functional groups, indicating significant vegetation influence on organic matter complexity. The sp²/sp³ carbon ratios (0.724 for Bunger Hills and 0.408 for Schirmacher Oasis) indicate a balance between potentially decomposable aliphatic and stable aromatic structures. Mineralization rates were significantly higher in soils with greater moisture retention, with cumulative CO 2 release reaching up to 150 mg CO 2 /kg -1 soil day¯¹ over a 30-day period. Overall, our work revealed complex relationships between the environmental conditions and soil characteristics that significantly influence biological activity, carbon storage, and organic matter structure.