Effects of Grazing Intensity on N and P Content in Dominant Plants and Soil in the Northeast Regions of Qinghai-Tibetan Plateau

An experiment was carried out to determine the effect of grazing intensity on N and P content in dominant plants and soil of summer grassland in the northeast regions of Qinghai-Tibetan plateau.The results showed that the grazing increased the nitrogen content in leaves of Polygonum viviparum,the nitrogen content was the highest under moderately grazing intensity,and the nitrogen content in leaves of Kobresia capillifolia decreased.The phosphorus content in leaves of Polygonum viviparumand Kobresia capillifoliafirstly increased and then decreased as the grazing intensity increased,the phosphorus content was the highest under moderately and slightly grazing intensities,respectively.The grazing increased the N∶P value of Polygonum viviparum and decreased the N∶P value of Kobresia capillifolia,indicating that the different plants had the different use strategy for nitrogen and phosphorus.Grazing affected the soil N content in soil of 0~10cm,and the soil N content was the lowest under moderately grazing intensity and was the highest at highly grazing intensity;however the grazing did not affect the soil N content when the soil depth was below 20cm.The soil P content firstly decreased and then increased with the increase of grazing intensity,the soil P content was the highest under moderately grazing intensity.The soil N∶P value did not varied greatly in the soil of 0to 20cm,and slightly varied in 20~30cm layer.