Abstract: In order to discuss the variation of the ecosystem respiration, soil respiration and carbon sink strength under grazing gradient, the biomasses in alpine weeds meadow lying to the north slope of Qilian mountain were observed from May, 2010 to December, 2011. Meanwhile the respiration of ecosystem and soil were tested by the static chamber. Results showed that(1)the respiration of ecosystem and soil had an exponential relationship with 5cm soil temperature significantly（P＜0.01）. The Q10 values of ecosystem respiration under light, moderate and heavy grazing were 4.28, 4.16 and 4.43 and the Q10 values of soil respiration were 3.33, 3.24 and 3.44, respectively.(2)Ecosystem respiration and soil respiration were higher in summer and lower in winter，carbon released from ecosystem respiration were 854.64, 909.79 and 811.70g·m-2·y-1 and released from soil respiration were 564.24, 606.92and 534.56g·m-2·y-1 respectively under light, moderate and heavy grazing; there was no significant difference of the carbon released between different grazing intensity.(3)Total net primary productivity which was 766.65, 707.75 and 570.36gC·m-2·y-1, carbon sink which was 351.93, 261.68 and 177.46gC·m-2·y-1 respectively under light, moderate and heavy grazing both reduced with grazing pressure. The alpine weedy meadow was a carbon sink whether under light grazing or heavy grazing, and carbon sequestration potential was huge. The results provide a basis for understanding the characteristics of carbon cycle of alpine weedy meadow in Qinghai Tibetan plateau.

Key words:  Alpine weedy meadow, Grazing pressure gradient, Net primary productivity reduces, Ecosystem respiration, Soil respiration, Carbon sink strength