Distribution characteristics of soil carbon during forage greening in different alpine grasslands of Eastern Qilian Mountains

Rhododendrons spp. brushland (DJ), Salix cupularis brushland (GL), Dasiphoru fruticosa brushland (JL), Polygonum viviparum grassland (ZY), Grass steppe (HC), Swamp grassland (ZZ) and Kobresia grassland (SC), which designate seven different alpine grassland types in the Eastern Qilian Mountains of Qinghai-Tibetan Plateau of Western China, were selected for soil carbon investigation (including microbial biomass carbon with Fumigation Extraction Method, soil organic matter and K₂SO₄-extractable carbon). The results show that the soil organic matter varies from 82.3 to 207.2 g·kg^-1 and is influenced by vegetation type. K₂SO₄-extractable carbon and microbial biomass carbon (MBC) range from 23.61 to 138.81 mg·kg^-1 and from 156.19 to 1 182.84 mg·kg^-1 extractable carbon to soil organic matter and MBC varies from 0.03% to 0.06% and from 9.97% to 18.46% respectively. Under brushland, the value of K₂SO₄-extractable carbon under GL is lower than that under DJ. Under grassland, however, that value under HC is lower than under ZY, ZZ and SC. MBC contribution to soil organic matter ranges from 0.19% ( under HC) to 0.48% (under JL), and the value for upper layer is greater than that for the lower layer, except under ZY and ZZ. MBC, which is higher in the upper layer than in the lower layer, has significant positive correlations (at P<0.05 or P< 0.01) with soil organic matter, total nitrogen and available phosphorus under the seven vegetation types. Furthermore, MBC has significant positive correlations with K₂SO₄-extractable carbon for brushland (at P<0.05) and for grassland (P<0.01). MBC also has significant positive correlations (P<0.01) with microbial biomass nitrogen and microbial biomass phosphorus under DJ, GL, JL, ZY, HC, ZZ and SC. MBC content and its contribution to soil organic matter are commonly different among sampling sites and soil layers. Furthermore, MBC is influenced by soil organic matter, K2SO4-extractable carbon, total nitrogen and available phosphorus.