Seasonal variations of concentration and δ<13>^C in soil air CO_2 and soil respired CO_2

Seasonal changes of δC of soil respired CO_2 and vertical profiles of soil air CO_2 concentration and δC are discussed at an urban deciduous forest in Nagoya City, central Japan. The δC values of soil respired CO_2,which were obtained by the isotopic mass balance using the chamber method, showed seasonal fluctuations ranging from -31.0 to -24.5‰ with low values from summer to autumn and high ones from winter to spring. Seasonal variation in soil air CO_2 showed high concentraiton and low δC value in summer, and low concentration and high δC value in winter. They ranged from 0.1 to 3.4% (0.8-3.0% in vertically) in concentration and from -23.7 to -18.1‰ (0.3-4.6‰ in vertically) in δC. CO_2 concentration in soil air increased gradually with depth, whereas the δC value decreased suddenly at the depth from 10 to 20cm and remained relatively constant below 20cm. The seasonal δC fluctuation of soil respired CO_2 was influenced by CO_2 production at a shallow depth in soil (C profiles in soil organic matter increased ca. 2‰ from 10 to 60cm in depth. This δCenrichment is much larger than the expected value from the isotopic fractionation during decomposition.
タンデトロン加速器質量分析計業績報告 Summaries of Researches Using AMS 2000 (平成12)年度