Determination of microbial versus root-produced CO₂ in an agricultural ecosystem by means of ´¹³CO₂ measurements in soil air

Abstract

The amounts of microbial and root-respired CO₂ in a maize/winter wheat agricultural system in south western Germany were investigated by measurements of the CO₂ mixing ratio and the 13C/12C ratio in soil air. CO₂ fluxes at the soil surface for the period of investigation (1993−1995) were also determined. Root respired CO₂ shows a strong correlation with the plant mass above ground surface of the respective vegetation (R2≥0.88); the maximum CO₂ release from roots was in August for the maize (2.0±0.5 mmol m−2h−1) and in June for winter wheat (1.5±0.5 mmol m−2 h−1). Maximum CO₂ production by roots correlate well with the maximum amount of plant root matter. Integrating the CO₂ production over the whole growing season and normalizing to the dry root matter yields, the CO₂ production per gram dry organic root matter (DORM) of maize was found to be 0.14±0.03 gC (g DORM)−1. At the sites investigated, root-produced CO₂ contributed (16±4)% for maize, and (24±4)% for winter wheat, respectively, to the total annual CO₂production in the soil (450±50 gC m−2 for maize, 210±30 gC m−2 for winter wheat).