Objective To understand the mixed litters decomposition characteristics of Pinus massoniana and native broad-leaved trees, and the relationship between the mass loss rate of mixed litter with the species and proportion of broad-leaved litter.

Method Based on the leaf litter of Pinus massoniana Lamb.(P), Cinnamomum camphora Presl.(C), Sassafras tzumu Hemsl.(S) and Toona sinensis Roem.(T), we conducted a two-year field needle-width mixed decomposition experiment of litter bags to study the mass loss of the pure litter of the above four tree species and their mixed litter, i.e., combining needles of one conifer with leaves of one, two or three broad-leaved species (i.e., PC, PS, PT, PSC, PST, PCT and PSCT, respectively), as well as including various ratios of these mixed litters in each treatment. There was a total of 35 treatments, including 31 mixed and 4 pure litter treatments.

Result After two years of decomposition, the combinations of PT, PC, PCT, PST and PSCT had higher mass loss rates of than PS and PSC. The mass loss rate of leaf litters generally showed a synergistic effect and it increased from the 6th to 18th month, and then declined thereafter. It was the highest (67.74%) at the 18th month of decomposition. Compared with other mixed litters, the mass loss rate of PT64, PCT721 and PSCT7111 showed a strong synergistic effect in 4 incubation periods. The results of regression analysis showed that the decomposition coefficient k and mixing effect were negatively correlated with the initial contents of total phenolic, lignin, cellulose, the ratios of C/N, C/P, lignin/N, and lignin/P. In contrast, they were positively correlated with the initial contents of N and P.

Conclusion Our results show that mixed litters with 30%-40% broad-leaved species, especially with the litter of T. sinensis, may benefit the litter mass loss of P. massoniana and promote the nutrient return to forest soils.