Stabilization of organic matter in topsoils under different tundra vegetation in central Spitsbergen (High Arctic)

Bacground and aims Soil organic matter (SOM) stability in Arctic soils is a key factor influencing carbon sequestration and greenhouse gas emissions, particularly in the context of climate change. Despite numerous studies on carbon stocks in the Arctic, a significant knowledge gap remains regarding the mechanisms of SOM stabilization and their impact on the quantity and quality of SOM across different tundra vegetation types. The main aim of this study was to determine SOM characteristics in surface horizons of permafrost-affected soils covered with different tundra vegetation types (pioneer tundra, arctic meadow, moss tundra, and heath tundra) in the central part of Spitsbergen (Svalbard). Methods Physical fractionation was used to separate SOM into POM (particulate organic matter) and MOM (mineral-associated organic matter ) fractions, while particle-size fractionation was applied to evaluate SOM distribution and composition in sand, silt, and clay fractions. Results The results indicate that in topsoils under heath tundra POM fractions dominate the carbon and nitrogen pools, whereas in pioneer tundra topsoils, the majority of the carbon and nitrogen are stored in MAOM fractions. Moreover, a substantial proportion of SOM is occluded within macro- and microaggregates. Furthermore, the results obtained from FTIR analysis revealed substantial differences in the chemical properties of individual soil fractions, both concerning the degree of occlusion in aggregates and across particle size fractions. Conclusions This study provides clear evidence that tundra vegetation types significantly influence both the spatial distribution and chemical composition of SOM in the topsoils of central Spitsbergen.