IMPACTS OF GRAZING INTENSITY ON NITROGEN POOLS AND NITROGEN CYCLE IN AN ALPINE MEADOW ON THE EASTERN TIBETAN PLATEAU

Grazers may influence nitrogen (N) pools and alter N inputs and outputs (losses) to the ecosystem in a number of ways. In this study, we evaluated N pools within the plant-soil system (0-30 cm) and soil N transformation under three different grazing intensities by yaks (light: 1.2, moderate: 2.0, and heavy: 2.9 yaks ha(-1)) in an alpine meadow on the eastern Tibetan Plateau. Total plant and soil N at 030 cm depth tended to increase as grazing intensity increasing (plant N: 26.6, 31.4 and 36.7 g m(-2); soil N: 905, 939 and 1125 g m(-2) for light, moderate and heavy grazing, respectively). Soil N transformation rates, such as net N mineralization, gross nitrification, denitrification and N2O emissions, generally increased under heavy grazing intensity. Results indicate that heavy grazing intensity accelerated the N cycling rates between system components and leaded to increases in plant-soil system N in this alpine meadow.