Responses Of Soil Organic Carbon, Nitrogen And Phosphorus To Simulated Warming And Nitrogen Application In Songnen Grassland

This thesis focuses on Leymus chinensis (Trin.) Tzvel. grassland in Songnen plain. We simulated warming by achieving with Infrared Radiator and nitrogen (N) application by receiving ammonium nitrate. We examined soil organic carbon, soil N,P responses to manipulations of four treatments: ambient, warming, N application, and warming plus N application during the periods from 2007 to 2008.After two growing seasons, the result showed that soil organic C responded to two single-factor treatments and warming plus N application treatment haven't significant differences from the ambient, but there are certain trends. Warming treatment was decreased soil organic C by 1.6%, extra N increased organic C by 5.4%. Warming was increased the content of soil NH4+ by 13.3% and was accelerated soil net N mineralization rate (NMR). N application was significantly increased the content of soil total N by 10.4%, available N by 14.4%, NH4+ by 19.4%, and was accelerated NMR; meanwhile, it was reduced the content of soil total P by12.9%, available P by 19.4%. The combined warming plus N application was sharply decreased NO3- by 60.3%; meanwhile, it was increased soil total N and NH4+ by 9% and by 45.2%. Compared with the ambient, warming and N application and warming plus N application were all increased total soil available N accumulation (TANA) significantly amongst two years. In response 2007, the TANA of four treatments were all have increasing trends in 2008, but not significantly.Soil total N content was significantly negatively linear correlated with soil total P and available P, but was positively linear correlated with soil NMR. Soil NMR was negatively linear correlated with soil available P, but was positively linear correlated with soil temperature (0-15-cm) and the ratio of N and P.Main form of available N in 0-15cm soil was NH₄⁺-N under warming plus N application. Soil temperature is the most important factor for NMR. It was obvious that extra N promoted the release of soil available N. Our study indicated that soil N content rise declined soil P that may partly explain that the increase of available N accelerates the absorption of plant to soil available P.The ratio of C : N, whereas, had a negative correlation with soil NMR, the reduced ratio of C : N may be explained by increasing decomposition speed of SOM and accelerating the nutrient return, by a lower rate of microbial N immobilization or a higher rate of microbial activity and releasing larger available N to plant. Because N is always a restrictive nutrient, and the growing of soil bacterial would restrict by C in the condition of low ratio of C : N; if soil N was enough, and N immobilization would reduce; in contrary, the growing of soil bacterial would restrict by N, and the mineral N was immobilized by bacterial rapidly.