Asymmetric effects between tree and understorey litters on mixed litter decomposition in temperate Quercus variabilis forest

Litter decomposition is a critical process of biogeochemical cycles of ecosystem. While growing evidences have shown the decomposition rates of litter mixture are different from those of single-species litters, the mutual effects between different functional type species in the mixture remain inconclusive. A field litterbag experiment was conducted to determine the mutual effects of three functional type plants [tree (Quercus variabilis), shrub (Lindera glauca), and herb (Lygodium japonicum)] during the decomposition in a temperate oak forest. After 400 days of in situ incubation, the mass loss rate of each species-specific in the mixture was greater than that decomposed as monoculture, showing the greatest mass loss in the three-species litter mixture. In addition, the decomposition constant for each species was stimulated while mixed with other species. The presence of L. glauca leaf litter significantly elevated total N (15.0%) and C loss (8.92%) of Q. variabilis leaf litter, and the existence of Q. variabilis leaf litter also led to enhanced total N (10.4%) and C (9.1%) release of L. glauca leaf litter. The addition of L. japonicum in the mixed litters showed substantially positive effects on total N (16.5% and 10.8%) and C (10.6% and 14.2%) release of both L. glauca and Q. variabilis litters. In contrast, neither Q. variabilis nor L. glauca litter exhibited effects on the total N and C loss of L. japonicum litter. Our results indicate that the mutual effects between different functional types on nutrient release were asymmetric in the mixed litters. The role of species-specific in the mixture should be highlighted while evaluated the nonadditive effects in the leaf litter mixing experiments.