Effluxes of nitrous oxide, methane and carbon dioxide and their responses to increasing nitrogen deposition in the Gurbantunggut Desert of Xinjiang, China
Aims Desert soils play an important role in the exchange of major greenhouse gas (GHG) between atmosphere and soil. However, many uncertainties existed in understanding of desert soil role, especially in efflux evaluation under a changing environment. Methods We conducted plot-based field study in center of the Gurbantunggut Desert, Xinjiang, and applied six rates of simulated nitrogen (N) deposition on the plots, i.e. 0 (N0), 0.5 (N0.5), 1.0 (N1), 3.0 (N3), 6.0 (N6) and 24.0 (N24) g·m~(-2)·a-1. The exchange rates of N_2O, CH_4 and CO_2 during two growing seasons were measured for two years after N applications. Important findings The average efflux of two growing seasons from control plots (N0) were 4.8 mug·m~(-2)·h~(-1),-30.5 mug·m~(-2)·h~(-1) and 46.7 mg·m~(-2)·h~(-1) for N_2O, CH_4 and CO_2, respectively. The effluxes varied significantly among seasons. N0, N0.5 and N1 showed similar exchange of N_2O in spring and summer, which was relatively higher than in autumn, while the rates of N_2O in N6 and N24 were controled by time points of N applications. The uptake of CH_4 was relatively higher in both spring and summer, and lower in autumn. Emission of CO_2 changed minor from spring to summer, and greatly decreased in autumn in the first measured year. In the second year, the emission patterns were changed by rates of N added. N additions generally stimulated the emission of N_2O, while the effects varied in different seasons and years. In addition, no obvious trends were found in the emission factor of N_2O. The uptake of CH_4 was not significantly affected by N additions. N additions did not change CO_2 emissions in the first year, while high N significantly reduced the CO_2 emissions in spring and summer of the second year, without affected in autumn. Structure equation model analysis on the factors suggested that N_2O, CH_4 and CO_2 were dominantly affected by the N application rates, soil temperature or moisture and plant density, respectively. Over the growing seasons, both the net efflux and the global warming potential caused by N additions were small.