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

摘要

We had continuously measured soil CO₂ efflux (R_s) in a larch forestin northern Japan at hourly intervals for the snow-free period in 2003 withan automated chamber system and partitioned R_s into heterotrophicrespiration (R_h) and autotrophic respiration (R_r) by using thetrench method. In addition, we applied the soil CO₂ concentrationgradients method to continuously measure soil CO₂ profiles undersnowpack in the snowy period and to partition R_s into topsoil (O_aand A horizons) CO₂ efflux (F_t) with a depth of 0.13 m and sub-soil(C horizon) CO₂ efflux (F_c). We found that soil CO₂ effluxeswere strongly affected by the seasonal variation of soil temperature butweakly correlated with soil moisture, probably because the volumetric soilmoisture (30–40% at 95% confidence interval) was within a plateauregion for root and microbial activities. The soil CO₂ effluxes changedseasonally in parallel with soil temperature in topsoil with the peak inlate summer. On the other hand, the contribution of R_r to R_s was thelargest at about 50% in early summer, when canopy photosynthesis andplant growth were more active. The temperature sensitivity (Q₁₀) ofR_r peaked in June. Under snowpack, R_s was stable until mid-March andthen gradually increased with snow melting. R_s summed up to79 gC m?2 during the snowy season for 4 months. The annual R_s wasdetermined at 934 gC m?2 y?1 in 2003, which accounted for 63%of ecosystem respiration. The annual contributions of R_h and R_s toR_s were 57% and 43%, respectively. Based on the gradient approach,R_s was partitioned vertically into litter (O_i and O_e horizons)with a depth of 0.01–0.02 m, topsoil and sub-soil respirations withproportions of 6, 72 and 22%, respectively, on an annual basis. Thevertical distribution of CO₂ efflux was consistent with those of soilcarbon and root biomass.