Increased soil nutrient availability, and associated increases in vegetation productivity, could create a negative feedback between Arctic ecosystems and the climate system, thereby reducing the contribution of Arctic ecosystems to future climate change. To predict whether this feedback will develop, it is important to understand the environmental controls over nutrient cycling in High Arctic ecosystems and their impact on carbon cycling processes. Here, we examined the environmental controls over soil nitrogen availability in a High Arctic wet sedge meadow and how abiotic factors and soil nitrogen influenced carbon dioxide exchange processes. The importance of environmental variables was consistent over the 3 years, but the magnitudes of their effect varied depending on climate conditions. Ammonium availability was higher in warmer years and wetter conditions, while drier areas within the wetland had higher nitrate availability. Carbon uptake was driven by soil moisture, active layer depth, and variability between sampling sites and years (R2 = 0.753), while ecosystem respiration was influenced by nitrogen availability, soil temperature, active layer depth, and sampling year (R2 = 0.848). Considered together, the future carbon dioxide source or sink potential of high latitude wetlands will largely depend on climate-induced changes in moisture and subsequent impacts on nutrient availability. wetland, climate change

Previous studies in tundra ecology provide evidence for sensitivity of the vegetation-soil complex to climate. Short-term experiments (less than or equal to10 yr) suggest that climate change may have a decade-scale effect on soil moisture, decomposition and nutrient availability, plant phenology, and plant growth. In contrast, there exists little evidence to confirm or refute the role of climate in structuring tundra vegetation over longer time scales (10 to 1000 yr). This study accordingly examines similar to1500 yr in the stratigraphy of two permafrost sediment cores from a High Arctic, polygon-patterned, graminoid-moss tundra. Present-day bryophyte-environment relationships are quantified, and the radiocarbon-dated macrofossil record of bryophytes is used to reconstruct past changes in soil moisture. The paleoecological record is characterized by pronounced variability during polygon development. As the hydrology of tundra polygons is controlled by known climatic and geomorphologic mechanisms, the recurrent development of polygon vegetation (cf. hydrologic change) is compared to an independent paleoclimatic proxy for net radiation (R-n). Based on this comparison, the vegetation provides support for a pronounced shift to colder and wetter conditions during the Little Ice Age (similar to300-465 yr BP), though the long-term response to past climate change is otherwise equivocal. We suggest accordingly that autogenic geomorphologic-vegetation processes may have been generally more important than climate in the long-term development of the polygon-patterned wetland examined. A framework for such processes is presented. We caution that previous research to simulate and describe the effects of climate warming might not have properly accounted for the dynamic role of geomorphology in regulating tundra microclimate.