Seasonal variability of soil CO2 flux and its isotopic composition (δ13C, δ14C, δ18O)

The flux and isotopic composition of soil CO2 were monitored at three sites in southern Poland, from January 1998 to January 2000. The sites represent typical ecosystems of central Europe: (i) mixed forest; (ii) a cultivated agricultural field, and (iii) grassland. Methods based on the inverted-cup principle were used. The flux of soil CO2 revealed distinct seasonal fluctuations, with maximum values up to approximately 30 mmol/m2/h during the summer months and around 90% lower during winter. Also, significant differences among the monitored sites were detected; the flux density was highest for the mixed forest site and about 50% lower for the cultivated grassland. Carbon-13 content of the soil CO2 revealed little seasonal variability, with δ13C values essentially reflecting the isotopic composition of the soil organic matter and the vegetation type. The 14C content of soil CO2 flux revealed slight seasonality, with lower δ14C values during winter. Significantly lower δ14C values were recorded at depth. (author)