Evidence of Nonlinearity in the Response of Net Ecosystem CO2 Exchange to Increasing Levels of Winter Snow Depth in the High Arctic of Northwest Greenland

Winter snowfall is increasing in many Arctic regions and climate models predict this trend will persist in the coming century. We examined the effects of two levels of increased winter snow accumulation on soil microclimate, plant and soil nutrient status, plant phenology and ecosystem CO2 exchange after five years of treatment in a widespread High Arctic ecosystem. Increased snow cover resulted in greater winter CO2 efflux, altered growing season soil nutrient availability and greater leaf nitrogen concentrations during the snow-free season. Modest increases in snow cover (+0.25 m above ambient) increased gross ecosystem photosynthesis (GEP) without increasing ecosystem respiration (ER), while the deepest snow cover (+0.75 m above ambient) increased both GEP and ER. The area of intermediate snow addition was a smaller source of CO, to the atmosphere during the growing season when compared to the ambient and deep snow areas. The intermediate and deep snow areas apparently had similar effects on the functioning of the vegetation community (increased GEP), but divergent effects on the soil microbial respiration, as evidenced by the changes in ER. This nonlinear response to increasing snow depth demonstrates the potential for complex High Arctic ecosystem responses to changes in winter precipitation.