Seasonal variations of concentration and δ ^C in soil air CO_2 and soil respired CO_2
摘要
Seasonal changes of δ<^13>C of soil respired CO_2 and vertical profiles of soil air CO_2 concentration and δ<^13>C are discussed at an urban deciduous forest in Nagoya City, central Japan. The δ<^13>C 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 δ<^13>C value in summer, and low concentration and high δ<^13>C 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 δ<^13>C. CO_2 concentration in soil air increased gradually with depth, whereas the δ<^13>C value decreased suddenly at the depth from 10 to 20cm and remained relatively constant below 20cm. The seasonal δ<^13>C fluctuation of soil respired CO_2 was influenced by CO_2 production at a shallow depth in soil (<10cm). On the other hand, the vertical δ<^13>C profiles in soil organic matter increased ca. 2‰ from 10 to 60cm in depth. This δ<^13>Cenrichment is much larger than the expected value from the isotopic fractionation during decomposition.