Abstract: Litter decomposition plays a vital role in carbon (C) cycling in wetlands, which is regulated by litter input characteristics, such as chemical traits and species diversity. Due to water level change and species invasion, plant community in Hongze Lake wetlands changes dramatically, subsequently exerting effects on litter inputs. In this study, we collected litters from four emergent macrophyte species widely distributed in Hongze Lake wetlands, i.e. Phragmites australis, Zizania latifolia, Alternanthera philoxeroides, and Paspalum paspaloides. We examined the effects of dominant species and evenness levels on litter mass loss and C mineralization rates. In the monocultures, P. australis had the lowest mass loss (22.2%) and C mineralization constant (k) (5.27×10^-4 d^-1), while P. paspaloides and A. philoxeroides had greatest mass loss (58.4% and 50.6%, respectively) and highest k values (9.52×10^-4 and 9.10×10^-4 d^-1, respectively). In terms of litter mixtures, A. philoxeroides and P. paspaloides dominated mixtures had greater mean mass loss (41.0% and 42.8%, respectively) and higher k values (8.84×10^-4 and 8.70×10^-4 d^-1, respectively), relative to P. australis and Z. latifolia dominated mixtures, with mass losses of 31.0% and 32.2%, respectively, and k values of 7.28×10^-4 and 8.07×10^-4 d^-1, respectively. With increasing evenness levels, litter mixtures dominated by P. paspaloides and A. philoxeroides exhibited a decreasing trend in mass loss and k values, but an increasing trend for P. australis dominated mixtures. In addition, litter mixtures often exhibited antagonistic effects on mass loss, but with additive or synergistic effects on C mineralization rates. These findings indicate the significant effects of dominant species and evenness level on litter decomposition at the community level in Hongze Lake wetlands, and highlight the vital role of non-additive effects during litter decomposition. Thus, the concern on litter mixture decomposition would contribute to an accurate evaluation on how freshwater wetland C cycling responds to changes of plant community.

Key words: litter decomposition, evenness, freshwater wetland, non-additive effect, emergent macrophyte.