Characteristics and influencing factors of soil dissolved organic carbon and nitrogen in a tropical seasonal rainforest in Xishuangbanna,Southwest China.

In order to clarify the seasonal and profile dynamics of soil dissolved organic carbon (DOC) and nitrogen (DN) contents, and to disclose the effects of soil temperature (T), soil water content (SWC) and pH on DOC and DN dynamics, we carried out a one-year study in a tropical seasonal rainforest in Xishuangbanna, southwest China. We measured soil DOC and DN content, T, SWC, and pH variation at soil depths of 0-20, 20-40, 40-80 and 80-100 cm in the fog-cool season (January), dry hot season (March), the beginning of rainy season (May), the middle of the rainy season (August) and the end of the rainy season (October) of one year. The results showed: from surface to the 60 cm depth along the soil profile, DOC and DN concentrations decreased; to the contrast, from the 60 cm to 100 cm depth, DOC and DN concentrations increased. The soil DOC and DN concentrations in the surface soil layer (0-20 cm) were the highest along the soil profile in the tropical rainforest. The seasonal variations of soil DOC and DN concentrations showed a higher value in the middle/later rainy season than in the dry seasons. But significant seasonal dynamics only occurred in soil DOC concentration at soil layers of 0-20 cm and 20-40 cm and in DN concentration at soil layer of 0-20 cm. The correlations between soil DOC/DN concentration and SWC and T were different among soil layers. There were significantly positive correlations between DOC concentration and SWC at soil layers of 0-20 cm and 20-40 cm, between DOC concentration and T at soil layers of 20-40 cm; while, SWC at 0-20 cm and 80-100 cm, and T at 0-20 cm had significantly positive correlations with DN concentration. Soil DOC and DN concentrations along the soil profile were not correlated with pH. The results indicated that the feedback of soil DOC and DN concentrations to SWC, T and pH at different soil layers along the profile varied.