Exchange of reduced volatile sulfur compounds between leaf litter and the atmosphere

Leaf litter collected from the uppermost litter horizon and the fermentation horizon from a 60-yr-old beech forest was investigated for its exchange of volatile reduced sulfur compounds with the atmosphere. A close linear correlation between the water content and the microbiological respiration was found. This biological activity was closely related to the exchange of dimethyl sulfide (DMS) and carbonyl sulfide (COS). We found a DMS emission exponentially correlated with the respiration rates of samples from both horizons. In contrast, COS was deposited to the leaf litter samples, and the uptake was not found to correlate linearly or exponentially with either the water content or the respiration rates. Deposition of COS was high when respiration was low. At higher respiration rates, as observed with increasing high water content, no COS uptake was detected. Under these conditions, we assume high levels of CO2, inferred from the high respiration rates observed, to cause a competitive inhibition of carbonic anhydrase, the well-known key enzyme for the consumption of COS. Though the enclosure technique results in gas exchange rates which provide an upper limit to the actual rates that might occur in situ within a forest, the measured exchange rates indicate that the contribution of the leaf litter to the atmospheric burden is not significant in the case of DMS but might be of relevance as a sink for COS.