Environmental factors controlling soil respiration in three semiarid ecosystems

Previous research suggests that soil organic C pools may be a feature of se miarid regions that are particularly sensitive to climatic changes. We inst ituted an 18-mo experiment along an elevation gradient in northern Arizona to evaluate the influence of temperature, moisture, and soil C pool size on soil respiration. Soils, from underneath different free canopy types and i nterspaces of three semiarid ecosystems, were moved upslope and/or downslop e to modify soil climate. Soils moved downslope experienced increased tempe rature and decreased precipitation, resulting in decreased soil moisture an d soil respiration las much as 23 acid 20%, respectively). Soils moved upsl ope to more mesic, cooler sites had greater soil water content and increase d rates of soil respiration las much as 40%), despite decreased temperature . Soil respiration rates normalized for total C were not significantly diff erent within any of the three incubation sites, indicating that under ident ical climatic conditions, soil respiration is directly related to soil C po ol size for the incubated soils. Normalized soil respiration rates between sites differed significantly for all soil types and were always greater for soils incubated under more mesic, but cooler, conditions. Total soil C did not change significantly during the experiment, but estimates suggest that significant portions of the rapidly cycling C pool were lost. While long-t erm decreases in aboveground and belowground detrital inputs may ultimately be greater than decreased soil respiration, the initial response to increa sed temperature and decreased precipitation in these systems is a decrease in annual soil C efflux.