CO₂ Flux in Arctic and Alpine Dry Tundra: Comparative Field Responses Under Ambient and Experimentally Warmed Conditions

Abstract

We compared growing season CO₂ flux patterns between botanically similar arctic and alpine dry tundra ecosystems in Alaska and Colorado under ambient and experimentally warmed conditions. Measurements were taken during the 1997 growing season, 3 yr after the warming treatments were begun. Under ambient weather conditions, arctic dry tundra at Toolik Lake, Alaska was a net source (4 g CO₂-C m²) of CO₂ to the atmosphere, while alpine dry tundra at Niwot Ridge, Colorado, was a net CO₂ sink (7 g CO₂-C m⁻²) during the growing season. Experimental warming of arctic tundra by 1 to 3°C, resulted in a sevenfold (32 g CO₂-C m⁻²) increase in this ecosystem's carbon source activity. Similar warming in alpine tundra changed this ecosystem from a net carbon sink to a net carbon source of 8 g CO₂-C m⁻² over the growing season. In the Arctic, increased CO₂ efflux with warming was largely the result of increased rates of ecosystem respiration throughout the entire growing season, while in the alpine ecosystem respiration increased only early in the growing season. Rates of photosynthesis were generally not affected by experimental warming at either site. These data suggest that global warming will accentuate the carbon source activity of dry tundra in the northern foothills of Alaska and will change the net CO₂ exchange of alpine dry tundra in the northern Rocky Mountains from a net CO₂ sink to a source.