[Changes of soil microbial biomass carbon and their impact factors for Pinus tabuliformis plantations at different development stages on the Loess Plateau, China.].

By taking an abandoned land as control and the young (13-15 year-old), middle-age (25-27 year-old) and mature (41-43 year-old) plantations of Pinus tabuliformis as research objects, the variation characteristics and impact factors of soil microbial biomass carbon (MBC) for the P. tabuliformis plantations in 0-60 cm soil layer were studied. Results showed that the average MBC at the young, middle-age and mature plantations was 93.08, 122.64 and 191.34 mg·kg, respectively, which showed a significant increase with growth stage and was significantly higher than the abandoned land (42.93 mg·kg). The average MBC contents gradually decreased with soil depth. Compared with the abandoned land, the average MBC at the young, middle-aged and mature plantations respectively increased by 134.2%, 221.7% and 375.7% in the 0-20 cm soil layer, 101.3%, 164.3% and 337.5% in the 20-40 cm soil layer, and 103.1%, 146.2% and 303.0% in 40-60 cm soil layer. The MBC for the whole soil layer of 60 cm had a highly significant correlation with the DBH, height and root biomass of the P. tabuliformis plantation, as well as the thickness, biomass and total nitrogen of litter. Meanwhile, the MBC also showed significant correlations with soil organic carbon (SOC), total nitrogen and moisture content. Principal component analysis showed that the root biomass, litter biomass and SOC were the principal factors affecting MBC. The P. tabuliformis plantation significantly increased SOC content mainly through litter of leaf and root and improved the MBC in the growth process.