Abstract: 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,P<0.01).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.

Key words: Grazing intensity, Altitudinal gradient, Net N mineralization, Qinghai-Tibetan Plateau

摘要： 通过对甘南州境内高寒草甸在4个放牧强度(禁牧、轻牧、中牧和重牧)和5个海拔梯度(3050,3180,3570,3600,3910 m)下的土壤氮矿化速率分析测定,并对室内和原位培养所得净氮矿化率进行比较,以期为确定该区合理的草地放牧管理措施,以及深入研究和系统评价高寒草甸生态系统碳、氮循环提供基础依据。结果表明:原位培养下,放牧强度的增强促进了土壤氮的矿化;室内培养所得土壤净氮矿化率大于原位培养净氮矿化速率,说明在适宜温度和湿度(22℃和40%~60%的田间持水量)条件下,氮矿化速率较高;作为土壤质量的一种度量,土壤氮矿化潜力在禁牧处理下较高(0.53 mg·kg^-1·d^-1),而在重牧处理下较低(0.36 mg·kg^-1·d^-1);随着海拔升高,氮矿化潜力呈"V"字型变化,而原位培养下的氮矿化率与海拔梯度呈显著负相关关系(R=-0.672,P<0.01)。处于强度放牧下的草地土壤氮素周转加快,造成土壤氮素水平下降;现阶段高海拔区土壤可看作养分的储存库,如果气候变化加剧,该养分库可能变成温室气体的源。

关键词: 放牧强度, 海拔梯度, 净氮矿化, 青藏高原