Abstract: By the method of carbon assimilation chamber, we measured the photosynthetic rate, dark respiration rate, and net carbon dioxide (CO₂) exchange of plant communities on the natural grasslands at different degradation levels and the artificial grasslands having been planted for different years in the Maqin County of Qinghai Province. On the natural grasslands at different degradation levels, the photosynthetic rate and dark respiration rate of plant communities had a variation trend of moderately degraded grassland < heavily degraded grassland < extremely degraded grassland < non-degraded grassland. A certain amount of CO₂ was absorbed by the plant communities on the non-degraded, moderately degraded, and heavily degraded grasslands, while 1.20 μmol CO₂·m^-2·s^-1 was released from the extremely degraded grassland. After the artificial restoration of the extremely degraded grassland, the CO₂ release reduced. The mono-cultured Elymus nutans grassland established in 2000 and 2004 absorbed much more CO₂ than did the mixed cultivated grassland established in 2002 and 2005. With the increasing established year of mono-cultured and mixed cultivated grasslands, the net CO₂ absorption by the plant communities decreased. From the viewpoint of carbon management in Qinghai-Tibet Plateau, it was suggested that the moderately and heavily degraded alpine grasslands should be prevented from being further degraded, and the extremely degraded alpine grassland should be artificially restored in time to effectively increase the CO₂ absorption by plant community.

Key words: Small-middle size soil animals, Diversity, Vertical distribution