Climate effects on the carbon balance of tussock tundra in the Philip Smith Mountains, Alaska

Abstract

Summary Net carbon dioxide exchange in the light and carbon dioxide efflux in the dark were observed at mid-season for tussock and intertussock tundra plant communities over diurnal courses on a four hour basis. Community carbon dioxide uptake was greater in tussock areas, but increased strongly in both areas with increasing photosynthetic photon flux density (PPFD) between 0 and 500 μmol m − 2 S −1 and tended toward saturation at higher PPFD due to low leaf area index. The low capacity for positive diurnal net CO 2 exchange identified for intertussock areas even under favorable environmental conditions is an important factor influencing the overall carbon balance of tussock tundra. Respiratory capacity is detertnined in tussock tundra soils by fluctuations in water table and depth of aeration, while instantaneous rates over the diurnal course are a function of the prevailing soil temperature profile. Flux rates were sitnilar to those from other sites in Alaskan coastral tundra, in Alaskan riparian tundra, and in tundra meadows in Greenland and Norway. Methane flux to the atmosphere was high from tussock areas with apparent transport via Eriophorum vaginatum but negligible in intertussock areas. Due to high rates of CO 2 efflux, the diurnal carbon balance was negative on days with periods of low light, especially in intertussock areas. However, carbon dioxide exchange in tussock tundra communities will vary strongly from year to year due to differences in rainfall, irradiance, and temperature. Because of interannual variations in climate and hydrology, long-term observations of CO 2 balance, spatial variation in water table, and carbon transport between communities must be considered before general conclusions may be made about the average carbon balance of a particular vegetation or landscape.