Impacts of grazing intensity on soil carbon and nitrogen in an alpine meadow on the eastern Tibetan Plateau

Different land-use strategies cause changes in soil carbon (C) and nitrogen (N) levels. This study aimed to determine seasonal changes in soil C and N contents and to investigate their transformations under three different grazing intensities (light grazing - LG 1.2, moderate grazing - MG 2.0 and heavy grazing HG 2.9 yaks ha(-1)) in alpine meadows oil the eastern Tibetan Plateau. This study substantiates significant seasonal differences of soil N contents but not to soil C contents. Averaged soil C and N values of all sampling dates were significantly higher in the HG site than in the LG and MG sites. Soil NO(3)(-)-N was highest at the HG site in June (8.16 mg kg(-1)) and lowest at the MG site in August (4.26 mg kg(-1)), while soil NH(4)(+)-N was highest at the HG site in August (12.57 mg kg(-1)) and lowest at the LG site in June (4.60 mg kg(-1)). Over the study period, soil N transformation rates, such as gross rates of nitrification, denitrification and N(2)O flux rate increased rapidly from June to July and then decreased until September. Generally, higher grazing intensities seem to cause higher soil N transformation rates. These results indicate that short-term heavy grazing has a better potential for soil C and N sequestration in alpine meadow systems.