Microtopography and Plant-Cover Controls on Nitrogen Dynamics in Hummock Tundra Ecosystems in Siberia

Abstract Earth hummocks constitute the most common surface structures of Arctic regions. In hummock tundra ecosystems, small mounds of earth alternate with depressions, the so-called interhummock areas. This study aimed at elucidating how differences in microtopography and associated variations in abiotic and biotic factors control biogeochemical cycles in hummock tundra soils. We assessed N pools and N transformation rates in hummocks and interhummock areas in the southern tundra subzone and along a soil-moisture gradient in the typical tundra subzone of the Taymyr Peninsula, Siberia, Russia. On a regional scale, N pools and transformation rates were positively related to latitude and therefore to temperature. Generally, wetter or waterlogged soil conditions tended to decrease gross mineralization rates and soil microbial N at least in interhummock areas. In contrast, at small spatial scales, soil microclimatic conditions were not the main determinant of the observed nitrogen cycling pattern. We found hi...