Acclimatization of soil respiration to warming in a tall grass prairie

The latest report by the Intergovernmental Panel on Climate Change (IPCC) p redicts a 1.4-5.8 degreesC average increase in the global surface temperatu re over the period 1990 to 2100 (ref. 1). These estimates of future warming are greater than earlier projections, which is partly due to incorporation of a positive feedback. This feedback results from further release of gree nhouse gases from terrestrial ecosystems in response to climatic warming(2- 4). The feedback mechanism is usually based on the assumption that observed sensitivity of soil respiration to temperature under current climate condi tions would hold in a warmer climate(5). However, this assumption has not b een carefully examined. We have therefore conducted an experiment in a tall grass prairie ecosystem in the US Great Plains to study the response of so il respiration (the sum of root and heterotrophic respiration) to artificia l warming of about 2 degreesC. Our observations indicate that the temperatu re sensitivity of soil respiration decreases-or acclimatizes-under warming and that the acclimatization is greater at high temperatures. This acclimat ization of soil respiration to warming may therefore weaken the positive fe edback between the terrestrial carbon cycle and climate.