Niels Peter Revsbech’s lab at Aarhus University has developed a novel CO2 microsensor. This sensor has a typical tip size of 30 µm and responds linearly from the detection limit of 0.0005 and up to 5 kPa pCO2. In addition to providing the first radial concentration profiles of CO2 in roots (Box 3 in the paper), we also used the CO2 microsensor to establish fluxes of respiratory CO2 between the roots and the surrounding medium. Based on simultaneous measurements of CO2 and O2 in the diffusive boundary layer enveloping the root (photo in Box 1 in the paper), the CO2 efflux can be calculated using a modified version of Fick’s 1st Law. Our study shows that the respiratory quotient of the roots increases from slightly above 1 with external O2 in the liquid medium at air equilibrium to around 5, when the external O2 supply is lowered to 3.7 kPa.
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