Soil COsub2/sub efflux of a larch forest in northern Japan

摘要

pstrongAbstract./strong We had continuously measured soil COsub2/sub efflux (iR/isubs/sub) in a larch forest in northern Japan at hourly intervals for the snow-free period in 2003 with an automated chamber system and partitioned iR/isubs/sub into heterotrophic respiration (iR/isubh/sub) and autotrophic respiration (iR/isubr/sub) by using the trench method. In addition, we applied the soil COsub2/sub concentration gradients method to continuously measure soil COsub2/sub profiles under snowpack in the snowy period and to partition iR/isubs/sub into topsoil (Osuba/sub and A horizons) COsub2/sub efflux (iF/isubt/sub) with a depth of 0.13 m and sub-soil (C horizon) COsub2/sub efflux (iF/isubc/sub). We found that soil COsub2/sub effluxes were strongly affected by the seasonal variation of soil temperature but weakly correlated with soil moisture, probably because the volumetric soil moisture (30a??40% at 95% confidence interval) was within a plateau region for root and microbial activities. The soil COsub2/sub effluxes changed seasonally in parallel with soil temperature in topsoil with the peak in late summer. On the other hand, the contribution of iR/isubr/sub to iR/isubs/sub was the largest at about 50% in early summer, when canopy photosynthesis and plant growth were more active. The temperature sensitivity (iQ/isub10/sub) of iR/isubr/sub peaked in June. Under snowpack, iR/isubs/sub was stable until mid-March and then gradually increased with snow melting. iR/isubs/sub summed up to 79 gC msupa??2/sup during the snowy season for 4 months. The annual iR/isubs/sub was determined at 934 gC msupa??2/sup ysupa??1/sup in 2003, which accounted for 63% of ecosystem respiration. The annual contributions of iR/isubh/sub and iR/isubs/sub to iR/isubs/sub were 57% and 43%, respectively. Based on the gradient approach, iR/isubs/sub was partitioned vertically into litter (Osubi/sub and Osube/sub horizons) with a depth of 0.01a??0.02 m, topsoil and sub-soil respirations with proportions of 6, 72 and 22%, respectively, on an annual basis. The vertical distribution of COsub2/sub efflux was consistent with those of soil carbon and root biomass./p.