Abstract:Although dissolved organic carbon(DOC) and nitrogen(DON) in soil have little proportion in the total carbon and nitrogen, they are the most important and active parts of soil organic matter(SOC). They could accelerate the weathering of minerals, supply the energy to the growth of microorganism and its decomposition, but also affect the validity and fluidity of nutrient substance in ecosystem. Compared with SOC, DOC and DON were more sensitive to reflect the chemical characteristics of soil, especially for indicating the quality and fertility level of soil. In order to study the characteristics of biodegradation of DOC and DON, the contents of DOC and DON in different fertility levels of Brown earth were determined. The results showed that the highest contents of DOC and DON in Brown earth were found in the native soil, the next was in the treatment of higher fertility and the lowest was in the treatment of lower fertility. The relations among DOC, DON, SOC, SON and soil microbial biomass carbon and nitrogen were remarkably positive correlation. The results also showed that DOC and DON were closely relevant with soil fertility, and could be regarded as the important indices of soil fertility. The decomposition rates of DOC and DON were faster at the initial stage of incubation and subsequently slower gradually. The decomposition data fitted a double exponential first-order decay model, which suggests that the DOC was comprised of tow fractions: a rapidly decomposable fraction with a turnover time of 1 day and a slowly decomposable fraction with a turnover time of about 400 days. And the DON was also comprised of two fractions: a rapidly decomposable fraction with a turnover time of about 2 days, and a slowly decomposable fraction with a turnover time of about 99-105 days. After the incubation of 42 days, the ratios of carbon to nitrogen in dissolved organic matter were enhanced.