Litter decomposition, residue chemistry and microbial community structure under two subtropical forest plantations: A reciprocal litter transplant study

Litter decomposition is a key process for ecosystem fertility and carbon (C) balance, key uncertainties remain about how this fundamental process is affected by microbial community composition. Evidence is growing that plant litter generally decays fastest at the site from which it was derived, owing to the presence of specialized microbial communities that can decompose specific types of litter. The objectives were to determine the impact of sites on litter decomposition and to examine the relationships among microbial community composition, litter chemistry, and decomposition rates of coniferous Cunninghamia lanceolata litter of higher lignin content and broadleaved Mytilaria laosensis litter of lower lignin content at different stages of decomposition under plantations of the respective species. The study was conducted for 16 months using a randomized split-plot design experiment with four replications of all combinations of treatments, the treatments being litter type and site (plantation species). The results showed that decomposition rates were the same for all combinations of amendments and sites, meaning that both sites had microbial communities equally capable or adapted to decompose plant substrates it had not previously encountered, despite marked differences in soil microbial communities between sites and the chemistry of the two litter types. Initial M. laosensis litter was of lower lignin content and C:N ratio and decomposed faster in the first 8 months than C. lanceolata litter under either M. laosensis or C. lanceolata forest. Litter decomposition was significantly slower in the environment from which it was derived between month 8 and month 16. This could be attributed to the exceptionally poor decomposition of M. laosensis litter which was significantly higher lingnin content at month 8 under M. laosensis than under C. lanceolata due to the impact of site on preferential degradation of litter C. Decomposers under C. lanceolata forest were more efficient in degrading alkyl C and/or less efficient in degrading O-alkyl C than those under M. laosensis forest during the experimental period, which might be related to the microbial community composition in the decomposing litter. Our study clearly showed interactions between changing litter chemistry and litter microbial communities and their impacts on litter decomposition. Site was not important in impacting decomposition rates, but played an important role in the preferential degradation of C components. However, further studies are needed to examine the conditions in forests where more rapid litter decomposition beneath the parent species than another species is considered to be common, in order to improve our ability to model decomposition globally.