How vegetation patches drive soil development and organic matter formation on polar islands

As Antarctica is strongly affected by climate change and global warming, the factors that mainly determine soil development might also shift from the dominance of physical to biochemical processes. Vegetation is restricted to the margins of the Antarctic continent with the Antarctic Peninsula being a region of patchily distributed vegetation. While on James Ross Island in the Weddell Sea only cryptogams can be found, on King George Island in the Southern Ocean also vascular plants are present. As rates of soil development and the build-up of soil organic matter are very low in these polar conditions, it can be hypothesized that vegetation patches comprise hot spots for biogeochemical soil processes. To analyze the effect of vegetation on soils in maritime Antarctica, we investigated vegetated and vegetation-free soils from both islands. On both islands, we found clearly higher carbon and nitrogen contents in vegetated soils. Using physical fractionation, we could demonstrate that the amount of free and occluded particulate organic matter is also higher in soils under vegetation, but at the same time, that clay-sized mineral-associated organic matter contributes most to carbon storage in all soils. The dominance of aromatic compounds in vegetation-free soils was disclosed by ¹³C NMR spectroscopy as well as a larger proportion of compounds with a lower molecular weight in vegetated soils. Thus, vegetation patches lead to soil organic matter containing higher amounts of bioavailable substrates that can be assumed to foster microbial activity and thus drive further soil development in a warmer future. However, in the cold arid environments a propagation of aridity might result in vegetation dieback and thus in a ceasing of biological soil activity driving a slowing of soil development.