Soil CO2 efflux of a larch forest in northern Japan

Abstract. We had continuously measured soil CO 2 efflux( R s ) in a larchforest in northern Japan at hourly intervals for the snow-free period in 2003 with an automated chamber system and partitioned R s into heterotrophic respiration ( R h ) and autotrophic respiration ( R r ) by using the trench method. In addition, we applied the soil CO 2 concentration gradients methodto continuouslymeasure soil CO 2 profiles under snowpackin the snowy period and to partition R s into topsoil(O a and A horizons) CO 2 efflux( F t ) with a depth of 0.13 m and sub-soil (C horizon) CO 2 efflux( F c ). We found that soil CO 2 effluxeswere strongly affected by the seasonal variation of soil temperature but weakly correlated with soil moisture, probably because the volumetric soil moisture (30–40% at 95% confidence interval) was within a plateau region for root and microbial activities. The soil CO 2 effluxeschanged seasonally in parallel with soil temperature in topsoilwith the peak in late summer. On the other hand, the contribution of R r to R s was the largest at about 50% in early summer, when canopy photosynthesis and plant growth were more active. The temperature sensitivity ( Q 10 ) of R r peaked in June. Under snowpack, R s was stable until mid-March and then gradually increased with snow melting. R s summed up to 79 gC m −2 during the snowy season for 4 months. The annual R s was determined 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 to R 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, topsoiland sub- soil respirationswith proportions of 6, 72 and 22%, respectively, on an annual basis. The vertical distribution of CO 2 effluxwas consistent with those of soil carbonand root biomass.