Litter mixing effects during decomposition remain inconclusive for boreal peatlands, and such effects may vary with climate warming and associated shifts in vegetation composition. Here, litters were collected from four common species (deciduous shrub Betula fruticosa , evergreen shrub Ledum palustre , graminoid Eriophorum vaginatum , and moss Sphagnum divinum) in a boreal peatland of northeast China, resulting in 15 species combinations with species richness ranging from one to four. We determined litter mixing effects on carbon (C) mineralization rate and mass loss under aerobic conditions at 10 °C and 20 °C in a 315-d incubation experiment, and assessed the differences in litter mass loss for the individual species within monocultures and mixtures. Non-additive effects on C mineralization and mass loss were prevalent during decomposition of litter mixtures. Moreover, the sensitivity of C mineralization and mass loss to rising incubation temperature (Q 10) was found to be non-additive in five and three out of 11 mixtures, respectively. Notably, mass loss of other litters in the mixtures was generally promoted by B. fruticosa , but inhibited by S. divinum in two- and three-species litter mixtures. Furthermore, B. fruticosa increased and S. divinum decreased Q 10 values for mass loss of other litters in four out of seven cases. These findings suggest that the shifts in plant community composition will not only influence community-level litter decomposition through altered litter mixing effects during decomposition, but also modulate the response of litter decomposition to rising temperature in boreal peatlands. • Non-additive effects were predominant during litter mixture decomposition. • Litter mixing effects on decomposition varied with incubation temperature. • B. fruticosa litter promoted mass loss of other litters in the mixtures. • S. divinum litter often inhibited mass loss of other litters in the mixtures. [ABSTRACT FROM AUTHOR]