• biosphere–atmosphere exchange;
  • carbonyl sulfide (COS);
  • gross CO2 exchange;
  • leaf gas exchange;
  • stomatal control


  • Carbonyl sulfide (COS) exchange in C3 leaves is linked to that of CO2, providing a basis for the use of COS as a powerful tracer of gross CO2 fluxes between plants and the atmosphere, a critical element in understanding the response of the land biosphere to global change.
  • Here, we carried out controlled leaf-scale gas-exchange measurements of COS and CO2 in representative C3 plants under a range of light intensities, relative humidities and temperatures, CO2 and COS concentrations, and following abscisic acid treatments.
  • No ‘respiration-like’ emission of COS or detectable compensation point, and no cross-inhibition effects between COS and CO2 were observed. The mean ratio of COS to CO2 assimilation flux rates, As/Ac, was c. 1.4 pmol μmol−1 and the leaf relative uptake (assimilation normalized to ambient concentrations, (As/Ac)(Cac/Cas)) was 1.6–1.7 across species and conditions, with significant deviations under certain conditions. Stomatal conductance was enhanced by increasing COS, which was possibly mediated by hydrogen sulfide (H2S) produced from COS hydrolysis, and a correlation was observed between As and leaf discrimination against C18OO.
  • The results provide systematic and quantitative information necessary for the use of COS in photosynthesis and carbon-cycle research on the physiological to global scales.