Contribution of microarthropods to the decomposition of needle litter in a Japanese cedar (Cryptomeria japonica D. Don) plantation

Japanese cedar (Cryptomeria japonica D. Don) plantations tend to have poor soil–litter conditions, which may influence the activity and composition of microbial and faunal communities in the soil–litter subsystems. The effects of microarthropods (Acarina and Collembola) on the decomposition processes of C. japonica needle litter were examined with litter mesh boxes over a 2-year period. After 5 months, the mass loss of needle litter in the fauna-excluded boxes (mesh size 25 μm) was significantly higher than that in the control boxes (mesh size 1 mm) but after 10 months, it was significantly lower than that in the control boxes. The density of total microarthropods, 77% of which were collembolans and oribatid mites (Cryptostigmata), was strongly correlated with the mass loss rate. The C/N ratios of the litter in the control treatments were significantly lower than those in the fauna-excluded treatments after 10 months. However, the presence of microarthropods in the boxes had no significant effect on the amounts of nitrogen immobilized in the litter. Annual decomposition rates (k) of needle litter were 0.377 in the control treatment and 0.298 in the fauna-excluded treatment. Based on Seastedt's equation (1984), microarthropods increased the decomposition rate of needle litter (kfauna/ktotal) by 21%. Our results indicate that microarthropods accelerate the overall decomposition rate of C. japonica needle litter, despite inhibiting decomposition temporarily.