Abstract: Soil labile organic carbon is the most active and important component in the global carbon cycle. To understand the seasonal variations of soil labile organic carbon and their main controlling factors in the poplar (Populus euramericana cv. I.72) plantations in coastal area of northern Jiangsu, five poplar plantations of 4-, 8-, 12-, 15- and 20-years old were selected as study sites, with the water-soluble organic carbon (WSOC), microbial biomass carbon (MBC), temperature, and moisture in 0-10, 10-25, and 25-40 cm soil layers determined. Overall, the soil WSOC and MBC in the plantations were higher in spring and summer, but lower in autumn and winter, especially in 0-10 cm soil layer. The WSOC was the maximum in spring and the minimum in autumn, while the MBC was the maximum in summer and the minimum in autumn or winter. The WSOC was significantly correlated with the MBC, but the WSOC and MBC had less correlation with soil temperature and soil moisture. The seasonal variations of the WSOC and MBC were not only affected by the seasonal variations of soil temperature and soil moisture, but also affected by the soil physical and chemical properties and the seasonal changes of ground-cover.

Key words: soil eco-toxicology, biomarkers, molecular diagnosis, detoxification mechanism.