Seasonal pattern of soil respiration and gradual changing effects of nitrogen addition in a soil of the Gurbantunggut Desert, northwestern China

- High midday temperatures in the summer could repress soil respiration.
- Precipitation could dramatically increase soil respiration.
- C sequestration was affected by the rate of N added and number of exposed years.

Evaluating the responses of soil respiration in desert ecosystems to varying rates of added N is of great significance for understanding their carbon (C) budgets under increasing nitrogen (N) deposition. In this study, the diel and seasonal patterns of soil respiration through out the growing season were examined over a three-year period after adding a gradient of N to soil in the Gurbantunggut Desert. N was added at five rates: 0.5, 1.0, 3.0, 6.0 and 24.0 g N m−2 y−1 (denoted as N0.5, N1, N3, N6 and N24, respectively), plus a control without N addition: N0. Soil respiration showed both a distinct diel and seasonal dynamics. Soil temperature was the dominant factor influencing diel changes in soil respiration. High summer temperatures could reduce soil respiration due to the probable decrease of microbial respiration. Soil moisture was the driving factor that affected the soil respiration seasonal pattern. Precipitation pulses elicited an intense CO2 release after the pulse ceased. Although soil respiration showed an increase with enhancing N rates in the first year, the positive effects of N24 treatments weakened in the second year and became negative, and effectively toxic in the third. The total carbon production in the growing seasons among different N treatments in 2010 and 2011 also followed this model. In addition, soil respiration was also consistent with fine root biomass in the growing seasons. The results indicated that as soil temperature interacted with soil moisture, it affected temporal changes in the soil surface C flux and C sequestration, with C sequestration being affected differently based on the rate of N added and number of exposed years.