Responses Of Meadow Soil Nitrogen Pool To Degradation And Simulated Warming In Wugong Mountain

Wugong Mountain meadow was typical and special in the vegetation vertical zone in the south of China with its characteristics of wide area and low level of distribution. But as tourists soared in recent years, tourists trample and waste emissions caused a large area of meadow degenerated in Wugong Mountain.This paper took Wugong mountain degraded meadow soil which caused by the tourists trampled as the research object, investigated the variation trends and their relationship of soil nitrogen and physical and chemical properties, and analyzed the effects of simulated warming on Wugong mountain meadow soil nitrogen mineralization. The aim was to take nitrogen as the breakthrough point, revealed the mechanism of meadow degradation influence on soil nutrient, and as a preliminary study on the response of Wugong Mountain meadow soil to global warming.At the altitude of 1900m selected sample plots:not degradation (CK,vegetation coverage>90%)^ lightly degradation (LD,60%<vegetation coverage<75%)?medium degradation (MD,30%<vegetation coverage<45%) and heavily degradation (HD,vegetation coverage<10%) meadow area, and along the slope the ridge line at the altitude of 1600m,1700m and 1800m, selected the sample plots of not degradation and heavily degradation meadow area.Used soil drilling, cutting ring and soil column method in soil sample collection. Soil samples were used to study the chemical, physical, and nitrogen mineralization of soils. The results showed that:(1) The soil TN, AN, NH4+-N, OC, exchange of acid, hydrolysis of total acid, the soil mass water content and total porosity in Wugong mountain heavily degradation meadow area was lower than that in no degradation meadow area, but soil NO3--N content and bulk density values had increased, indicated the meadow vegetation and soil heavily degradation changed the relationship between soil physical and chemical properties compared with the non degraded meadow:The related relationship between soil TN and NO3--N?AN and NH4+-N?soil bulk density and TN, AN, NH4+-N?the mass water content and four forms of nitrogen soil total porosity and TN, AN, NH4+-N from significant correlation to no significant correlation(P>0.05). The related relationship between the soil total porosity and NO3--N from non significant correlation to extremely significant positive correlation (P<0.01). The correlation of soil acidity, organic carbon, cation exchange capacity and soil nitrogen became weakened.(2) The study found that the content of TN, AN, NH4+-N, exchange of acid, hydrolysis of total acid, OC, cation exchange capacity would first increase and then decrease with the aggravation of degradation. The water content, total porosity and pH value would decrease gradually with the increase of degradation.But the N03"-N content and soil bulk density increased gradually with the increase of degradation. The biggest influence factor in CK, LD, MD and HD of meadow degradation stage on soil nitrogen were:the quality of soil moisture content, soil exchangeable acidity, soil organic carbon and soil hydrolytic acidity.(3) Study on soil nitrogen mineralization of Wugong Mountain found that at the same temperature, the rate of net nitrogen mineralization increased with the aggravation of degradation. Under the condition of the same elevation and degradation degree, the soil net nitrogen mineralization rate was significantly increased from 15? to 25?(P<0.05),and slightly reduced from 25? to 35?,Overall performance as 25?>35?>15?. Thus, it cloud be predicted that the peak value of soil net mineralization in Wugong Mountain meadow might appear between 25??30?.In conclusion,we consider that the meadow degradation which caused by the tourists trampled will lead to the soil TN, AN and NH4+-N content decreasing, the NO3--N content increasing and accelerating the mineralization of soil nitrogen. In addition, under the trend of global change, the increase of temperature will also accelerate the occurrence of soil nitrogen mineralization, promote the release of inorganic nitrogen, and accelerate the loss of soil nitrogen, affect the absorption of nitrogen in plants, and thus hinder the normal growth and development of plants, which accelerated meadow degradation, into a vicious spiral.