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A new continuous integrated cavity output spectroscopy analyzer and an automated soil
chamber system were used to investigate the exchange processes of carbonyl sulfide (OCS) between soils
and the atmosphere under laboratory conditions. The exchange patterns of OCS between soils and the
atmosphere were found to be highly dependent on soil moisture and ambient CO2 concentration. With
increasing soil moisture, OCS exchange ranged from emission under dry conditions to an uptake within an
optimum moisture range, followed again by emission at high soil moisture. Elevated CO2 was found to have a
significant impact on the exchange rate and direction as tested with several soils. There is a clear tendency
toward a release of OCS at higher CO2 levels (up to 7600 ppm), which are typical for the upper few
centimeters within soils. At high soil moisture, the release of OCS increased sharply. Measurements after
chloroform vapor application show that there is a biotic component to the observed OCS exchange.
Furthermore, soil treatment with the fungi inhibitor nystatin showed that fungi might be the dominant OCS
consumers in the soils we examined. We discuss the influence of soil moisture and elevated CO2 on the OCS
exchange as a change in the activity of microbial communities. Physical factors such as diffusivity that are
governed by soil moisture also play a role. Comparing KM values of the enzymes to projected soil water CO2
concentrations showed that competitive inhibition is unlikely for carbonic anhydrase and PEPCO but might
occur for RubisCO at higher CO2 concentrations.
