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The grassland in Inner Mongolia,one of the largest remaining grassland ecosystems in the world,is extensive and covers an area of up to 68% of the entire region.Recently,with the increasing needs of livestock products,the ecological function of the grassland is severely degraded by overgrazing.The effect of grazing has become an urgent and crucial issue in the study of grassland ecology.The early researches mainly focused on the effects of grazing on the productivity,community structure and biodiversity of the grasslands through the browsing,trampling around and excretion of livestock.Focusing on C4 soil or plants,only a few studies have considered the effects of grazing on the stoichiometry traits of soil and plants.The mechanism by which grazing affects the stoichiometry traits of soil and plants is far from clear.For this issue,we carried out a study considering the role of grazing on the stoichiometry traits of soil and plant at both population and community scales.We determined the C,N,P content and the C/N ratios of plant and soil to explore how grazing affects the stoichiometry traits and nutrient cycling rates in an ecosystem.We found that:(1) On community scale,C,N,P content of the leaves had no-significant difference between the grazed and the exclosure grassland;however,on species scale,the N content in the grazed grassland was significantly higher than that in the exclosure.(2) Grazing significantly decreased soil total carbon(TC),total nitrogen(TN),soil organic carbon(SOC) and available phosphorus,increased the nitrate nitrogen,with no effects on total phosphorus(TP) and ammonium nitrogen.(3) The C/N ratio of the plant in grazed grassland was significantly lower than that in the exclosure,suggesting higher decomposition rate of litter and quicker nutrient cycling rate of the ecosystem.In conclusion,our study indicates that plants can adapt to varied environments caused by grazing through choosing suitable strategies of nutrient using.

In large scale,plant stoichiometry is mainly affected by latitude and longitude.Many works has have been done to study the effects of temperature on plant stoichiometry along the latitude gradient,while researches on the precipitation along the longitude gradient are rare.In this research,we studied the stoichiometry characteristics of grassland communities along the longitude gradient in Hulunbeir.The results showed as follow: 1)the range of leaf carbon was 440.76—452.72 mg/g,leaf nitrogen was 17.79—30.88 mg/g,and leaf phosphorous was 1.31—1.71 mg/g.Both the leaf carbon and C/N ratio significantly increased with the increasing longitude.Leaf nitrogen significantly decreased with the increasing longitude,and leaf phosphorous showed an increasing tendency,however,the relationship between leaf phosphorous and longitude was not significant.The amount of carbon,nitrogen and phosphorous of grassland communities significantly increased with the increasing longitude.2)For the 0—10cm soil depth,total carbon,total nitrogen,total phosphorus and organic carbon were significantly affected by precipitation and increased with longitude;however,soil ammonium nitrogen(NH+4-N) and nitrate nitrogen(NH-3-N) were less affected by precipitation and didn′t change significantly with longitude.3)Soil total carbon,organic carbon,total nitrogen,total phosphorus and available phosphorus did not have significant effects on plant leave carbon,nitrogen and phosphorus,but had a significant effects on the amount of carbon,nitrogen and phosphorous of grassland communities.In this studied region,soil available phosphorus was 8.13 mg/ kg,which was higher than the Global Average Value(7.65 mg/kg),but the average leaf phosphorous was 1.5 mg/g and lower than the Global Average Value(1.77 mg/kg).Our research suggested that variation in leaf carbon,leaf nitrogen and leaf phosphorus concentration and its strong correlation with precipitation reveal that,to some extent,stoichiometry characteristics at the community level are adaptive to local precipitation condition.The amount of carbon,nitrogen and phosphorus of grassland communities have a high relationship with the local precipitation,and have a significant correlation with soil total carbon,total nitrogen,total phosphorus.The shortage in soil available phosphorus is not the major factor for the low plant leaf phosphorus concentration in our studied region,and the low plant leaf phosphorus is a result of adaptation.