Abstract: Wedelia biflora is a climbing herb in family Asteraceae. It has shown an “invasion” trend in the Xisha Islands, endangering the safety of native vegetation and ecosystem. With the expansion of W. biflora, its litter mixes with that of local dominant tree species. To explore this mixture effect on litter decomposition and nutrient release of native dominant tree species, we conducted a litter decomposition experiment in the mixed forest of Pisonia grandis and Guettarda speciosa using litterbag method. We investigated mass loss and nutrient release of mixed litters from native dominant trees (P. grandis and G. speciosa) and W. biflora. The results showed that the decomposition rate of W. biflora litter was faster than that of native dominant trees, due to its higher litter quality \[i.e. higher nitrogen content (12.1 g·kg^-1), lower carbon-nitrogen ratio (35.0), and ligninnitrogen ratio (10.7)\] than the native dominant trees’ litter. When the native dominant trees’ litter was mixed with W. biflora litter, the substrate quality of the mixed litter was improved, which resulted in increased mass loss and release of carbon, nitrogen, and phosphorus during litter decomposition. The results indicate that W. biflora expands and mixes its litter into the native forests, accelerating mass loss and nutrient release of dominant trees’ litter. Such an effect may reduce soil erosion mitigation effect of dominant trees’ litter in Xisha Islands, accelerate nutrient leaching, and ultimately affect ecological balance.

Key words: Wedelia biflora, Xisha Islands, litter decomposition, nutrient release.