Effects Of Experimental Nitrogen Addition On Soil Enzyme Activities In Temperate Grassland Of Inner Mongolia

Under the background of global change, soil carbon sequestion abilityenhancement is helpful to reduce CO2in the atmosphere and alleviate global warming.Atmospheric nitrogen (N) deposition has been increased rapidly due to fossil-fuelburning and fertilizer application. China has become the third largest N depositionarea after Europe and North American. Elevated nitrogen deposition resulted in soilnitrogen inputs has been increased significantly, moreover, excessive nitrogen inputsmay have an impact on global warming, grassland vegetation growing and its litterdecomposition. Besides, excessive nitrogen imputs may lead to soil acidification,biodiversity decreasing and a series of negative effects. At present, the effects ofnitrogen deposition on forest and field ecosystem have been studied in popular,however, little is known about the relationship between nitrogen deposition and soilenzyme activities in temperate typical grassland in Inner Mongolia.In this paper, nitrogen addition experiments was conducted to investigate theinfluence of different nitrogen rates (0,56,112,224,392,560kg N ha-1.yr-1) on soiland microaggregates enzyme (βG, NAG, LAP, AP) activities of temperate typicalgrassland in Xilinguole Inner Mongolia, China. During the6-year experimental period,the results are as follows:1. In bulk soil, increasing nitrogen rate decreased βG, NAG, LAP activity, butdid not have significant effect on AP activity. Besides, βG, NAG, LAP activity hadthe lowest values at the N560(560kg N ha-1.yr-1) nitrogen addition treatment.2. In bulk soil, increasing nitrogen rate decreased pH, but increased ammoniumnitrogen content. pH is positive related to βG, NAG, LAP activity, but negativelyrelated to AP activity and ammonium nitrogen is positive related to AP activity, butnegatively related to βG, NAG, LAP activity.3. In bulk soil, increasing nitrogen rate increased soil organic carbon contentssignificantly when nitrogen addition is over112kg N ha-1.yr-1.4. In microaggregates, increasing nitrogen rate did not have significant effect onβG, NAG and AP activity, but decreased LAP activity significantly at392kg N ha-1.yr-1nitrogen addition treatment.5. In microaggregates, increasing nitrogen rate decreased pH but increasedammonium nitrogen content, and pH is positive related to βG, NAG, LAP, APactivity, but ammonium nitrogen is positive related to βG, NAG, AP activity,negatively related to LAP activity. 6. In microaggregates, organic carbon contents decreased significantly whennitrogen addition is over56kg N ha-1.yr-1, making a negative effect on soil carbonstorage.