Microbial Activities Responses To Simulated Warming And Nitrogen Application

This thesis focuses on Leymus chinensis (Trin.) Tzvel. grassland in Songnen plain. We simulated atmospheric warming using Infrared Radiator and simulated nitrogen (N) deposition by applying ammonium nitrate. We examined the biomass of microorganisms, the enzyme-activity , nutrient of soil which responses to manipulations of four treatments: ambient, warming, N application, and warming plus N application during the periods from 2007 to 2008.The results indicated that, to some extent, both warming and nitrogen application had various influence on the biomass of soil microorganisms. The soil bacterial biomass was increased by 15.6% due to the warming treatment and increased by 16% due to the extra N. And the extra N also made actinobacteria biomass increased by 28.8%, but made the Fungal biomass decreased by 10.8%. Both the warming and nitrogen application made Bacterial biomass increased by 11% and actinobacteria biomass by 24.1%, but made fungal biomass decreased by 18.8%. The effect on bacterial biomass from the warming and nitrogen application had great interaction. N application could inhibit the growth of fungi sharply.N application made the activity of the urease and phosphatase increased by 34.4% and 33.5%, while it inhibited the cellulase-activity and made it decreased by 15.5%.Warming made phosphatase-activity increased by 55.8%, but it had no significant effect on cellulose and urease. Both the warming and nitrogen application had significant effect on cellulose and urease, one was sharply decreased by 19.1%, the other was greatly increased by 44.1%. The effect on bacterial biomass from both the warming and nitrogen application had great interaction.The total N of soil content was significantly positively linear correlated with Bacterial biomass and actinobacteria biomass. The ratio of C/N, whereas, had a positive correlation with Fungal biomass. And the significantly positively linear correlation was also existed in urease and phosphatase of the total N of soil content, so does cellulose as the ratio of C/N.