Soil microbial biomass, nutrient availability and nitrogen mineralization potential among vegetation-types in a low arctic tundra landscape

Arctic plant communities vary greatly over short distances due to heterogeneities in topography and hydrological conditions across the landscape. Recent evidence suggests substantial changes in vegetation including increasing shrub cover and density in the Arctic over the past three decades that may be in response to climate change. We investigated soil microbial biomass, nutrient availability, nitrogen (N) mineralization potential and nitrification potential in four of the principal vegetation-types across the low Arctic: dry heath, birch hummock, tall birch and wet sedge. Soil total carbon (C) and N contents, microbial biomass C, dissolved organic C (DOC) and N (DON), mineral N, and N mineralization potential differed considerably among vegetation-types. Tall birch and wet sedge soils had significantly higher DON, mineral N, and N mineralization potential than birch hummock or dry heath soils. Soil N mineralization potential across all soils was positively correlated with soil available C and N, and negatively correlated with soil total C:N ratios. Nitrification potential was negligible in all soils. These results demonstrate close relationships between soil biogeochemical properties, mineral N supply rates, and vegetation-types across an arctic landscape. Our soil N mineralization data suggest that climate warming may enhance N availability in tall birch soils more than in birch hummock soils, and therefore that increases in shrub densities across the landscape are most likely within and directly around current tall shrub patches.