Effects Of N Addition And Tibeten-sheep Rotational Grazing On Vegetation And Soil Of Alpine Meadow On Qinghai-Tibiten Plateau

Alpine meadow is the most sensitive ecosystem for grazing and nitrogen addition in Qinghai-Tibet Plateau.In this study,we conduct with Tibetan sheep and researched the effects of 3 stocking rates(0,24 month sheep/ha,48 sheep month/ha)and 4nitrogen additions levels(0 kg/ha,50 kg/ha,100 kg/ha,200 kg/ha)on soil and vegetation of alpine meadow.Main results are as follows:(1)Effects of nitrogen addition and Tibetan-sheep rotational grazing on soil of alpine meadow in Qinghai-Tibetan Plateau.Nitrogen addition increased the soil total nitrogen content in the first year(p=0.037),but the soil total nitrogen content was decreased(p=0.079)in the following years,and the response of soil organic carbon had a similar trend.The response of soil total phosphorus to nitrogen addition treatments was not obvious.The soil total carbon and total nitrogen content were negatively correlated with stocking rates(TN:p=0.028,SOC:p=0.009),but the relationship between total phosphorus and grazing rates was not significant(p=0.311).(2)Effects of nitrogen addition and Tibetan-sheep rotational grazing on dominant populations of alpine meadow in Qinghai-Tibetan Plateau.Nitrogen addition could improve the biomass of dominant populations,but,there was no significant effect on height and density.In 2012-2014,the density Kobresia capillifolia increased first and then decreased,and the maximum value showed in 24sheep month/ha.Elymus nutans density(2012:R2=0.7967,p=0.024;2013:R2=0.812,p=0.048;2014:R2=0.9643,p=0.032),and height(2012:R2=0.6411p=0.002;2013:R2=0.5546,p=0.005)were significantly correlated with stocking rates.(3)Effects of nitrogen addition and Tibetan-sheep rotational grazing on community of alpine meadow in Qinghai-Tibetan Plateau.In 2012-2014,aboveground biomass of alpine meadow(Y)with nitrogen addition level first increased and decreased later,y=-0.0031x2+0.7954x+94.272,(R~2=0.7555,p=0.043),and peak value occurred at 128.3kg/ha nitrogen addition.Aboveground biomass reduced with increasing stocking rates(p=0.042),and caused Elymus nutans,Aster alpinus L.,Anemone rivularis var.flore-minore to disappear.Biomass of sedge and grass decreased with increased of stocking rates,but the proportion of total biomass increased with stocking rates decreased first and then increased.The evenness of grassland had the lower sensitivity in a rainy year than a drought year.Shannon-Weiner diversity index(Y)increased is correlation with stocking rates(X),y=-0.0002x2+0.0123x+2.9458,(R~2=0.874,p=0.041).Redundancy analysis show that grazing,nitrogen addition,annual average temperature and rainfall have a main influence on the productivity of alpine meadow,but annual average temperature and rainfall have a negative effect.The SEM show that nitrogen addition has a negative effect on the soil total nitrogen,soil organic carbon and species richness,but it has a positive effect on the aboveground biomass;grazing play a positive role in species richness and soil total nitrogen,but has negative effect on the soil total carbon and biomass,grazing can affect the species richness by aboveground biomass.Nitrogen addition can reduce the adverse effects of grazing on the alpine meadow,combination of nitrogen addition and grazing can conducive to the stability of soil and vegetation of alpine meadow.