Vegetation Community, Foliar Nitrogen, and Temperature Effects on Tundra CO2 Exchange across a Soil Moisture Gradient

Abstract

Soil moisture has both direct and indirect effects on carbon dioxide (CO2) exchange in tundra vegetation. It directly affects vegetation distribution and functioning, thus CO2 exchange at the leaf level, and it controls microbial decomposition influencing soil respiration. In this study we investigated CO2 exchange on a heterogeneous tundra landscape in the Canadian low arctic with the primary purpose of exploring the relationship between moisture variability and community level fluxes. CO2 exchange was measured with a portable chamber system, along with soil and air temperature. Biomass, leaf area, and foliar nitrogen were determined from harvested vegetation. Fluxes were compared in birch, tussock, heath, and sedge communities under different moisture regimes. Respiration and productivity were typically highest in wet or mesic groups, with fewer differences in net CO2 exchange. Across the soil moisture gradient, productivity and net CO2 exchange per unit leaf area and foliar nitrogen showed a significant negative linear trend. Respiration was limited in very dry and saturated soil, and soil temperature effects on respiration were seen only in mesic moisture conditions. These findings indicate that nutrient and temperature affects on fluxes can be at least partially explained within the framework of soil moisture availability.