Abstract: In subtropical plantations, plant litters often experience repeated dry-wet cycles. To explore the influence of dry-wet cycles on litter-derived dissolved organic carbon (DOC), we conducted a 40-day laboratory incubation experiment with leaf litters from six deciduous broad-leaved tree species, four evergreen broad-leaved tree species, and two evergreen coniferous tree species from typical subtropical plantations of China. There were three treatments: dry (maintaining mass ratio of litter∶water below 20∶1), wet (maintaining mass ratio of litter∶water at 1∶1), and dry-wet (drying for four days and rewetting for four days, with a total of five cycles). To assess the effects of dry-wet cycles on DOC quantity and characteristics, we investigated the variations of leaf litter-derived DOC amount and spectral characteristics (specific ultraviolet absorbance at 254, 284, and 350 nm), and litter mass loss. The results showed that litter mass loss was greater in the wet and dry-wet treatments than in the dry treatment, and that leaf litter mass loss under dry-wet treatment was comparable to that under wet treatment. For both deciduous and evergreen broad-leaved species, litter-derived total DOC production in the dry-wet treatment was higher than that in the dry treatment, but was lower than that in the wet treatment. However, litter of evergreen coniferous trees had lower total DOC production in the dry-wet treatment than in the dry and wet treatments. Litter-derived DOC had higher specific ultraviolet absorbance at 254, 284, and 350 nm in the wet and dry-wet treatments than in the dry treatment, indicating a greater aromatic degree of DOC. These findings suggest that repeated dry-wet cycles are an important factor controlling the quantity and quality of litter-derived DOC in subtropical plantations.

Key words: litter decomposition, aromatic degree, leaching, tree species, subtropical forest.