Effects of warming and changing precipitation rates on soil respiration over two years in a desert steppe of northern China

Soil respiration (R (s)) has become a central issue in global carbon cycle research. In this study, we determined the seasonal changes in soil carbon efflux and the underlying mechanism with regard to the effects of abiotic and biotic factors in a degraded steppe ecosystem. A warming treatment and a control, and three watering levels were applied using a free air temperature increase facility. R (s) was measured throughout the year, and soil nutrition properties, as well as microbial biomass carbon were determined over the growing season. R (s) rates were significantly higher during the growing season than the non-growing season; however, the warming treatment led to a marked increase in R (s) in the winter. Soil temperature and R (s) were described by an exponential function with a Q (10) of 1.92 (R (2) = 0.74, p < 0.01); root respiration (21.9 %) was lower than heterotrophic respiration (78.1 %). Soil organic carbon, soil moisture, root biomass, and soil ammonium-N were determined to be driving R (s) during the growing season. The most important factor was soil organic carbon content in the 0-10 cm soil layer, with soil moisture showing little direct effect on R (s). Soil environmental variables including temperature, moisture, nutrition status, root growth, and soil microbial activity might co-regulate soil carbon emission, which would be considered critical in assessing the carbon balance under climatic change in arid areas.