CARBON POOLS AND FLUXES ALONG AN ENVIRONMENTAL GRADIENT IN NORTHERN ARIZONA

Carbon pools and fluxes were quantified along an environmental gradien t in northern Arizona. Data are presented on vegetation, litter, and s oil C pools and soil CO2 fluxes from ecosystems ranging from shrub-ste ppe through woodlands to coniferous forest and the ecotones in between . Carbon pool sizes and fluxes in these semiarid ecosystems vary with temperature and precipitation and are strongly influenced by canopy co ver. Ecosystem respiration is approximately 50 percent greater in the more mesic, forest environment than in the dry shrub-steppe environmen t. Soil respiration rates within a site vary seasonally with temperatu re but appear to be constrained by low soil moisture during dry summer months, when approximately 75% of total annual soil respiration occur s. Total annual amount of CO2 respired across all sites is positively correlated with annual precipitation and negatively correlated with te mperature. Results suggest that changes in the amount and periodicity of precipitation will have a greater effect on C pools and fluxes than will changes in temperature :in the semiarid Southwestern United Stat es.