Seasonal variation in CO_2 production of leaf litter from different deciduous forests at the early decomposition stage

摘要

We collected leaf litter from a deciduous broadleaf forest and a larch forest in Hokkaido, Japan naturally without using litter traps or litter bags. The litter collection was conducted every month from October 2001 through October 2002 except in thesnowy season. We measured the CO_2 production rate of the litter samples through microbial respiration using the chamber method in a laboratory under different temperature and moisture conditions to investigate the seasonal pattern and temperature and moisture responses of CO_2 production at the early stage of litter decomposition. Seasonal variation was found in the CO_2 production rate per unit of litter dry weight (P_(dw)), or the litter decomposition rate, for both broadleaf and larch litters. Although seasonal patterns differed somewhat according to temperatures and species, P_(dw) reached the minimum in June. The moisture sensitivity of P_(dw) decreased with time and reached the minimum in summer for both broadleaf and larch litters, whereas theseasonal pattern of the temperature sensitivity (Q_(10)) was not clear. The seasonal pattern of P_(dw) was explained by its C: N ratio for broadleaf litter. For larch litter, however, the relationship between P_(dw) and the C:N ratio was complicated because of fresh litterfall supplied gradually before defoliation. The temperature and moisture sensitivities of P_(dw) changed in parallel with the C:N ratio for both broadleaf and larch litters, respectively. These facts suggest the importance of litter chemical quality in the early decomposition process of fresh litter and the validity of the C:N ratio as an index of litter quality.