Response Of Litter Decomposition And Soil Biological Activity To Increased Temperature And Nitrogen Deposition In The Songnen Grassland

As the main feature of the global environment, global warming and nitrogen deposition gradually become the focus of attention of the public and the scientific community, and they have even more profound impacted on ecological activities of terrestrial ecosystems. Litter decomposition, soil enzymes and soil microbial systems are the most active bioactive substances for material circulation and energy flow process on land ecosystem. Northeast Songnen Leymus chinensis meadow soil as research subject, we studied that how nitrogen addition, warming or nitrogen addition+ warming impact on litter decomposition, soil microbial activity and soil enzyme activity, using simulated global warming and nitrogen deposition.The main results can be summarized as follows:1. Warming, N addition and warming + N addition all stimulated litter decomposition. As rates of litter decomposition increase with warming and N addition in temperate meadow grasslands, the turnover times of C, N and P from the litter to soil will decrease. This has the potential to increase the storage of C, N and P in the soil, and might alter the timing and availability of these nutrients for plant growth.And plant species with different litter qualities should be considered when modeling C and N cycles and nutrient dynamics in grassland ecosystems. In addition, Leymus chinensis is expected to contribute more than Phragmites australis to C and N cycling and nutrient dynamics in the semi-arid Songnen grasslands.2.Cellulase activity was redused year by year, N addition and warming inhibited the cellulase activity in some degrees, but inhibition of warming was more pronounced.Urease activity reduced year by year, N addition significantly increased the urease activity,warming increased the urease activity in spring and autumn, but inhibited the urease activity in summer, warming and N addition interaction performed to promote. Phosphatase activity increased year by year, N addition and warming both promoted the phosphatase activity, warming and N addition interaction performed to promote.3.The content of soil microbial biomass C(MBC), N(MBN) and P(MBP)showed a single peak trends change with the season change, and more in the summer,less in the spring and fall. N addition, warming and N addition + warming all increased MBC and MBC significantly, but reduced the MBP significantly.Thereforein the Songnen grassland, warming and N addition were in favor of microorganisms to fix C and N, but had disadvantage effect to fix P.4.Cellulase activity was significantly positively related to soil C, N addition,warming and N addition + warming all made the correlation between cellulose activity and soil C content lower. Urease activity was significantly positively related to soil N and available nitrogen, but the correlation between urease activity and soil available nitrogen higher. Three ways made the correlation between urease activity and soil N, available nitrogen lower. Phosphatase activity was significantly positively related to soil P and available phosphorus, but the correlation between phosphatase activity and soil P higher. Three ways made the correlation between phosphatase activity and soil P, available phosphorus lower. MBC was positively correlated with soil C, N addition made the correlation between MBC and soil C content lower, but warming and N addition + warming both made it higher. MBN was positively correlated with soil N and available nitrogen, but the correlation with soil available nitrogen higher. Three ways made the correlation with soil N lower, with available nitrogen higher. MBP was positively correlated with soil P and available phosphorus,three ways made the correlation with soil P and available phosphorus higher. MBC was positively correlated with cellulase activity, warming and N addition + warming both made the correlation higher. MBN was positively correlated with urease activity,N addition, warming and N addition + warming all made the correlation lower. MBP was positively correlated with phosphatase activity, N addition and N addition +warming both made the correlation higher.5.Litter decomposition rates of Leymus chinensis and Phragmites communis were positively correlated with soil enzyme activity and microbial mass. Warming, N addition and warming + N addition made the correlation between litter decomposition rates of Leymus chinensis and soil enzyme activity, microbial mass higher, the correlation between litter decomposition rates of Phragmites australis and phosphatase activity higher, warming made the correlation between litter decomposition rates of Phragmites communis and cellulase activity, microbial mass lower, N addition made the correlation between litter decomposition rates of Phragmites australis and cellulase activity, urease activity, microbial mass higher.