Abstract: Water extractable organic carbon (WEOC) is sensitive to climate change, and thus plays a vital role in carbon cycling in forest ecosystems. Here, the effects of soil warming (+5 ℃) on soil WEOC extracted by three different methods were examined in a subtropical forest. Concentrations of WEOC extracted by cold water (C_WEOC) and salt solution (S_WEOC) were not affected by soil warming. Soil warming reduced the concentration of WEOC extracted by hot water (H_WEOC) by 51.2% at the 0-10 cm soil layer, but elevated H_WEOC by 67.1%, 781.7%, and 501.6%, respectively, at the 10-20, 20-40 and 40-60 cm soil layer. Soil warming increased microbial biomass carbon (MBC) by 98.2% and 163.1% at the 20-40 and 40-60 cm soil later, respectively, but had no effect on MBC at the 0-10 and 10-20 cm. There was a significant difference in soil WEOC concentrations extracted by the three different methods. Generally, the concentration of C_WEOC was the lowest among the three extraction methods, and H_WEOC and S_WEOC were the highest in surface soil layer and deep layer, respectively. The significant effect of soil warming on WEOC could be ascribed to warmingstimulated deeper rooting, which enhance root carbon input and microbial activity in the subsoil and thus induce a decrease of WEOC in the topsoil and an increase of WEOC in the subsoil. Different extraction methods could be used together to reflect different origins and transformations of WEOC. These results could facilitate our understanding of the responses of soil carbon cycling to climate change in subtropical forests.

Key words: trend analysis., fiber quality, spatial and temporal distribution, cotton