Soil nitrogen cycling and vegetation dynamics associated with arctic patterned-ground features.

摘要

Patterned ground (surfaces that display ordered and relatively symmetrical morphological patterns) is common in regions of permafrost. Small patterned-ground features, such as non-sorted circles and small non-sorted polygons occur throughout arctic tundra. These features are small, between 0.1 to 3 m in diameter, with little to no vegetation, that lack a border of stones. In some areas small patterned-ground features can make up 80% of the ground surface at a local scale. Although these features are less vegetated relative to the surrounding stable tundra, vegetation can accumulate on their surfaces under favorable conditions. The availability of nitrogen is also a major limitation to the growth of arctic tundra vegetation. Few studies have examined the importance of nitrogen to growth of vegetation on patterned ground features, and instead have focused on the role of physical disturbance, such as frost heave, on the vegetation. In addition to lacking vegetative cover, these features lower amounts of soil organic matter, which cause differences in the soil properties, especially in regard to plant-available nitrogen.;In this study I examine soil nitrogen cycling and its interaction with vegetation communities associated with patterned-ground features in arctic tundra. At a regional-scale, soil N cycling is controlled by two important arctic boundaries: the pH boundary between moist acidic and moist nonacidic tundra, and the boundary between the Low and High Arctic. However N cycling in small-patterned ground features differs from that of the surrounding stable tundra, indicating that different factors may control biogeochemical cycling across very small spatial extents. N availability is limiting to plant communities on non-sorted circles. However, this response is reduced relative to the surrounding tundra, likely because of the greater frost heave that occurs in non-sorted circles. Long-term modeling simulations show that the combination of N availability and frost heave produce less plant biomass on non-sorted circles relative to stable tundra, in addition to plant communities that are dominated by plant types able to resist the disturbance associated with frost heave. Overall, this study provides insight into the importance of N as a controlling factor of the vegetation on small patterned-ground features.