The Effect of Altered Summer Precipitation on CO2 Loss from Forest and Rangeland Soils in Northern Utah

Soils represent the largest carbon (C) reservoir of terrestrial ecosystems. The ability of soils to hold on to this soil organic carbon (SOC) depends on climate and C quality. The SOC dynamics in forest and range ecosystems in montane areas of the Intermountain West are still poorly understood, as is their response to global climate change. This study addresses how C quality, influenced by vegetation type, and increased summer precipitation affect the rate of SOC losses via respiration in forest-rangeland soils in Northern Utah. We measured soil respiration from conifer, aspen, sagebrush, and grassland soils in untreated control plots and plots receiving summer irrigation in 2004 and 2005. The soil respiration rates varied with vegetation cover and with soil moisture as well as soil temperature. They were generally highest under aspen, lowest in grassland soils, and intermediate in conifer and sagebrush soils. Respiration increased in all soils immediately (1 day) after irrigation, but this response declined with time and varied among vegetation types. Our results imply that SOC in different vegetation types may vary in sensitivity to climate changes