Primary productivity and its main affecting factors of Alpine meadows on the Tibetan plateau

Alpine meadows and shrublands are approximately 7×108 hm2 which is about 50% of the natural grasslands on the Tibtean plateau and accounts for about 16.2% of the total grassland area in China. Alpine meadow is dominated by Kobresia meadow,including K.humilis meadow,Potentilla fruticosa shrub meadow,Kobresia tibetica meadow,K.parva meadow and K.pygmaea meadow. The average aboveground biomass of the five meadows was 354.2,422.4,445.1,227.3 and 368.5 g/m2,respectively,while the belowground biomass of 0-40 or 0-50 cm soil depth was 3 389.6,3 548.3,11 922.7,4 439.3 and 5 604.8 g/m2,respectively. Their ratios of belowground and aboveground biomass were 10.55,10.15,27.82,14.82 and 15.21 respectively,which were much higher than that of the default value(2.8±95%)recommended by IPCC(2006). The belowground biomass or belowground net primary productivity was more sensitive to the climate change and heavy grazing than above-grassland biomass did. Drought and heavy grazing decreased the ratio of belowground to aboveground biomass,even its value was less than 2 under extreme degradation conditions. Natural restoration is possible for light or moderate degraded alpine meadow for 3-8 years. However,it should be re-constructed for heavy or extreme degraded alpine meadow due to soil quality decrease and poison plant species and weeds invasion.