Abstract: In order to understand the effects of tillage regimes after mulching with rice straws on soil total organic carbon (TOC) and labile organic carbon (LOC) contents in bamboo (Phyllostachys edulis) stands, we investigated the organic carbon contents in 0-50 cm soil layer of bamboo stands in Huangyan District of Taizhou, Zhejiang Province. The treatments were set as bamboo stands mulched continuously for two years with (MST) and without soil scarification (MWST), and natural growth bamboo (CK). The results showed that compared with the CK treatment, soil TOC and light fraction organic matter (LFOM) increased by 8.7%-43.8% and 22.2%-90.8%, 13.2%-111.0% and 36.7%-238.5%, when treated with MST and MWST respectively. The easilyoxidized carbon (EOC) content in the depth of 0-50 cm MST soils was enhanced by 21.9%-97.5% compared to CK condition, whereas the EOC content was enhanced obviously in the depth of 0-20 cm MWST soils, but decreased in the depth of 20-50 cm soils. In addition to the significant differences in 10-20 cm soil layer, the change of watersoluble organic carbon (WSOC) was not obvious in other soil layers under the three treatments. The ratio of soil WSOC to TOC in CK condition was higher than in the other two treatments. The ratio of EOC to TOC in depth of 0-20 cm soil layer displayed in order of  MWST > MST > CK, and this ratio in the 20-50 cm soil layer decreased in the order of CK > MST > MWST. The correlation between each LOC and TOC reached a significant level (P<0.01) under all treatments. Under the three treatments, soil TOC, WSOC, EOC, and LFOM exhibited significant (P<0.05) or extremely significant (P<0.01) correlations with soil nutrients (total nitrogen, hydrolyzable nitrogen, available phosphorus, available potassium, exchangeable calcium, exchangeable magnesium).

Key words: ecological security assessment, Pressure-State-Function-Response (PSFR), watershed aquatic ecosystem, mountainous river