Soil Characteristics and Plant Functional Groups across Successional Stages of Ice-wedge Degradation and Re-stabilization in the Tundra of Northern Alaska

Abstract:

Recent warming has resulted in ice-wedge thaw in polygonal landscapes of northern Alaska, leading to changing topography and hydrology. Soil warming, coupled with altered hydrology, influences the availability and transport of nitrogen, with consequential impacts on vegetation. Nutrient cycling and availability can vary substantially across successional stages of ice-wedge degradation and re-stabilization. Resultant changes in plant communities and biomass can lead to feedbacks of further degradation or stabilization. This study aims to understand how carbon and nitrogen in soils and vegetation interact across ice-wedge successional stages at two sites in coastal Arctic Alaskan tundra (Jago River and Prudhoe Bay). Jago is an acidic coastal Arctic tundra site with great topographical gradient and heterogeneity, with distinct vegetation types across distinct successional stages of ice-wedge degradation. Prudhoe Bay is an alkaline, urban site with less topographic gradient, less distinct successional stages, and less distinct vegetation types across stages. We used buried bags and resin probes to measure soil moisture, total soil C and N, net N mineralization, and soil NO₃^- and NH₄⁺ at the drier ice-wedge successional sites. We harvested plant biomass from each successional stage, and Eriophorum angustifolium was used as a benchmark species to compare across sites. Jago soils had greater soil %N by mass compared to Prudhoe Bay, but due to differences in bulk density, Prudhoe Bay soils had greater total N and C. At Jago, N uptake (resin probes) was greater at sites with some degree of degradation, but the opposite was true for Prudhoe Bay. There is a clear shift in plant functional groups toward dominance by hydrophilic sedges and mosses with increasing degradation at both locations, and greater overall vegetation biomass at Jago. At Jago, the N content of E. angustifolium foliage is elevated in degrading sites, but this is less distinct at Prudhoe Bay. These data suggest that ice-wedge degradation may affect soil characteristics by increasing N availability and transport in sites that have experienced degradation, and therefore may play a key role in vegetation response to climate warming in dynamic, heterogeneous Arctic ecosystems; these trends however may be heavily dependent on specific local conditions.