Source of Soil Carbon Dioxide in a Forest Area byUsing Specific Activities of 14C and Carbon Isotopic Compositions

摘要

Sources of soil CO2 were studied through combining specific activities of 14C and δ13C values in soil CO2, an organiclayer on soil surface, soil organic matter and atmospheric CO2 in a forest area in Yinabu, Aichi prefecture, Japan. Thespecific activities of 14C are indicated by Δ14C values. The Δ14C value of soil CO2 at a deeper horizon (53 - 73 cm) was muchlarger than that of soil organic matter and approximately same as that of organic layer, which suggests that main source of thesoil CO2 at the deeper horizon is not soil organic matter decomposition but root respiration based on similarity in the Δ14Cvalue between the organic layer and live root. The δ13C of soil CO2 at a shallower depth (0 - 13 cm) was larger than that ofeither soil CO2 derived from the soil organic matter decomposition and the root respiration; and smaller than that ofatmospheric CO2. This result implies that atmospheric CO2 entered into soil air is one source of soil CO2 at the shallowerdepth besides both the soil organic matter decomposition and the root respiration. A Keeling plot based on concentrations andδ13C values of soil CO2 further showed that the sources of soil CO2 are atmospheric CO2, soil organic matter decompositionand root respiration at the shallower depth and only both soil organic matter decomposition and root respiration at the deeperhorizon, respectively. Based on mass balance approaches of the Δ14C and δ13C, the root respiration was testified to be themain source of the soil CO2 at the deeper horizon.