Determination of microbial versus root-produced CO2 in an agricultural ecosystem by means of δ13CO2 measurements in soil air

The amounts of microbial and root-respired CO 2 in a maize/winter wheat agricultural system in south western Germany were investigated by measurements of the CO 2 mixing ratio and the  13 C/ 12 C ratio in soil air. CO 2 fluxes at the soil surface for the period of investigation (1993–1995) were also determined. Root respired CO 2 shows a strong correlation with the plant mass above ground surface of the respective vegetation (R 2 ≥0.88); the maximum CO 2 release from roots was in August for the maize (2.0±0.5 mmol m −2 h −1 ) and in June for winter wheat (1.5±0.5 mmol m −2 h −1 ). Maximum CO 2 production by roots correlate well with the maximum amount of plant root matter. Integrating the CO 2 production over the whole growing season and normalizing to the dry root matter yields, the CO 2 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 CO 2 contributed (16±4)% for maize, and (24±4)% for winter wheat, respectively, to the total annual CO 2 production in the soil (450±50 gC m −2 for maize, 210±30 gC m −2 for winter wheat). DOI: 10.1034/j.1600-0889.2000.d01-1.x