CLIMATE EFFECTS ON THE CARBON BALANCE OF TUSSOCK TUNDRA IN THE PHILIP-SMITH-MOUNTAINS, ALASKA

Net carbon dioxide exchange in the light and carbon dioxide efflux in the dark were observed at mid-season for tussock and intertussock tund ra plant communities over diurnal courses on a four hour basis. Commun ity carbon dioxide uptake was greater in tussock areas, but increased strongly in both areas with increasing photosynthetic photon flux dens ity (PPFD) between 0 and 500 mu mol m(-2) s(-1) and tended toward satu ration at higher PPFD due to low leaf area index. The low capacity for positive diurnal net CO2 exchange identified for intertussock areas e ven under favorable environmental conditions is an important factor in fluencing the overall carbon balance of tussock tundra. Respiratory ca pacity is determined in tussock tundra soils by fluctuations in water table and depth of aeration, while instantaneous rates over the diurna l course are a function of the prevailing soil temperature profile. Fl ux rates were similar to those from other sites in Alaskan coastral tu ndra, in Alaskan riparian tundra, and in tundra meadows in Greenland a nd Norway. Methane flux to the atmosphere was high from tussock areas with apparent transport via Eriophorum vaginatum but negligible in int ertussock areas. Due to high rates of CO2 efflux, the diurnal carbon b alance was negative on days with periods of low light, especially in i ntertussock 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 variati ons in climate and hydrology, long-term observations of CO2 balance, s patial variation in water table, and carbon transport between communit ies must be considered before general conclusions may be made about th e average carbon balance of a particular vegetation or landscape.