Soil N Mineralization of An Alpine Meadow in Eastern Qinghai-Tibetan Plateau

This study reports an understanding of the N mineralization in soil of an alpine meadow in Qinghai-Tibet Plateau(Gannan Tibetan Autonomous Prefecture,Gansu Province),the net N mineralization rates in soil under four grazing treatments(No grazing,Light grazing,Moderate grazing and Heavy grazing) were determined from both indoor and in-situ incubation.The net N mineralization rates in soil from 5 different altitudes(which are 3050,3180,3570,3600,3910 m) were also determined.Results showed that the net N mineralization rate obtained from the indoor incubation was larger than that from the in-situ incubation,which indicated that the N mineralization rate was increased under appropriate temperature and moisture.Grazing increased the N mineralization under the in-situ incubation.Soil N mineralization potential was higher under the no-grazing treatment(0.53 mg·kg-1·d-1),and lower under the heavily-grazing treatment(0.36 mg·kg-1·d-1) compared to control.The N mineralization potential showed a V type with the elevation increasing.The net N mineralization rate in soil under in-situ incubation was negatively correlated with elevation(R=-0.672,P0.01).Conclusions are that severe grazing accelerates the turnover rate of nitrogen in soil,thus causes the soil nitrogen level decreasing.Therefore,the high altitude soil may be the nutrient pool at present.