The results showed that there was a mean of 27.26% DW of soluble matter in the freshly fallen leaves, which was rapidly leached out during the early stage of decomposition. The process of leaching could be divided into three stages: fast stage, relatively stable stage and extensive stage. In the fast leaching stage, about 87% of original soluble matter was lost, giving rise to a loss of 24% of the initial leaf dry weight. The duration of the fast leaching stage, which considerably decreases with increasing water temperature, was average of 36d in spring, 13d in summer, 17d in autumn and 56d in winter, roughly equivalent to 5/7 of the half—time of leaf decomposition. Therefore, leaching was evidently responsible for both the rapid loss of leaf dry weight and the most significant differences between seasonal decomposition rates in the early decomposition stage.