Soil CO2 concentration and efflux from three forests in subtropical China

Measurements of soil CO2 efflux and soil CO2 concentration concurrently are important for understanding the mechanism and regulation of CO2 in the soil. We have analysed CO2 concentration in a soil profile and soil CO2 efflux in three typical forests in subtropical China: monsoon evergreen broad-leaved forest (BF, 400 years old), pine and broad-leaved mixed forest (MF, 80 years old), and pine forest (PF, 70 years old). A portable soil CO2 sampler of simple sample operation was designed and used. The seasonal patterns of soil surface CO2 efflux and soil CO2 concentration were observed, and were positively correlated with rainfall, soil temperature, and moisture. The mean values of soil CO2 concentrations at the 15, 30, 45, and 60 cm soil depth were higher in BF (3368-9243 mu LL-1) than in MF (1495-7662 mu LL-1) and PF (1566-5730 mu LL-1), while the mean values of soil surface CO2 efflux (Rsurface) were 0.55 +/- 0.11 gm(-2) h(-1) in BF, 0.52 +/- 0.10 gm(-2) h(-1) in MF, and 0.45 +/- 0.07 gm(-2) h(-1) in PF. Soil CO2 concentration and Rsurface increased gradually with the age of the forests, but the incremental increase in soil CO2 concentration will be greater than that of Rsurface in MF and PF compared with BF. The data suggested that, although older forests have more C, younger forests probably will sequester C as CO2 faster than older forests.