Seasonal Variations and Influencing Factors of Gross Nitrification Rate in Desert Steppe Soil

Nitrification plays an important role in nitrogen (N) turnover and N cycling. To date, there have been many studies on the net N turnover in grassland. However, few studies have specifically focused on the gross N turnover, which is mainly due to methodological limitations. Here, we set up an enclosed plot in a desert steppe and determined the gross nitrification (GN) rate of the soil by using the barometric process separation method. We found the seasonal dynamics of the GN in the desert steppe soil, such that the GN in the summer (117.65 +/- 24.86 mu g N kg(-1) h(-1)) was significantly greater than in the spring and autumn (65.17 +/- 7.33 mu g N kg(-1) h(-1)), and it peaked in July (213.75 +/- 44.66 mu g N kg(-1) h(-1)). Additionally, the GN was lowest in the spring, with a means of 50.52 +/- 3.95 mu g N kg(-1) h(-1). The seasonal variation in the GN was different than the seasonal variation in the net nitrification rate, and the GN was generally much higher than the net nitrification rate. We further demonstrated that the soil moisture, temperature, bulk density and NH4+-N were the main factors that influenced the seasonal variations in the GN, and that the soil moisture had the greatest impact on the GN among all the factors measured.