Underestimation of soil respiration in a desert ecosystem

Soil respiration (Rs), conventionally considered as net soil CO2 flux, is an important link in the terrestrial carbon cycle. However, existing estimates of Rs in drylands may be erroneous, because of the abiotic soil CO2 flux. This may seriously hamper our understanding of the carbon cycle of desert ecosystems. In this study, we monitored CO2 flux of natural and sterilized soils, and obtained the net and abiotic soil CO2 flux in a desert ecosystem in Ningxia, China, and then computed Rs by using these data. Daily Rs was much larger than the net soil CO2 flux both in the growing and non-growing season. Further analysis indicated that Rs was controlled by soil temperature (Ts) over the annual cycle, and an exponential model could provide a good prediction of Rs. During the growing season, Rs increased significantly with rising soil water content (VWC) (P < 0.05). A bivariate (Ts and VWC) exponential-power model had a better performance for predicting Rs in the growing season than a Ts-only model. However, during the non-growing season, this model failed to simulate Rs. Our results suggest that Rs is greatly underestimated, and the exponential model is more applicable for annual Rs prediction.