Abstract: Reclaiming land from lake is a kind of human disturbance emerged in large numbers in China since the 1950s. Taking the Xiaodian Lake area in Taihu Lake as a case, this paper measured the concentrations and proportions of microbial biomass carbon (MBC), water soluble organic carbon (WSOC), readily oxidizable carbon (ROC), and particulate organic carbon (POC) in 0-40 cm soil layer after 35 years of reclaiming and under different land use types, aiming  to understand the characteristics of soil labile organic carbon in the reclaimed land area of Taihu Lake. The concentration and proportion of soil MBC in cropland were significantly higher than those in three kinds of forestland, with its concentration in 0-10, 10-20, 20-40 cm layers being 573.38±18.28, 335.52±53.35, and 109.33±4.86 mg·kg^-1, and 2.07, 2.02, and 1.39 times higher than that in Cinnamomum camphora forestland, 2.26, 2.79, and 2.01 times higher than that in Metasequoia glyptostroboides forestland, and 1.89, 2.10, and 1.21 times higher than that in Phyllostachys heterocycla forestland, respectively, which indicated that the disturbance of cultivation and fertilization in cropland had great effects on soil microbial activity. No significant differences in the concentrations and proportions of soil WSOC, ROC, and POC were observed between cropland and  Compared with those in the mountain forestlands of the same climate zone, the proportions of soil WSOC (1.22%-3.03%) and ROC (10.56%-30.64%) in the reclaimed land area were higher, but the proportion of soil POC (3.43%-17.28%) was lower, implying that the soil organic carbon in reclaimed land had a poor stability. As a kind of human disturbance, reclaiming land from lake altered the carbon cycle of natural ecosystem significantly, which should be taken into full account.

Key words: Poplar tree, Fine root, Biological cycling, Dynamics change