REDUCED SULFUR COMPOUND EXCHANGE BETWEEN THE ATMOSPHERE AND TROPICAL TREE SPECIES IN SOUTHERN CAMEROON

We measured the concentrations of reduced sulfur compounds in the atmo spheric boundary layer over an equatorial African rain forest. Results obtained from a dirigible hot air balloon and a tethered balloon syst em in the early morning hours reflect a multilayered structure of the atmospheric boundary layer with gradients of COS and CS2 indicating an uptake/production of these trace gases by the soil/vegetation system. In addition, we studied emission and deposition fluxes of volatile re duced sulfur compounds from tropical tree species using cuvettes to di rectly measure the exchange behavior of tree twigs. These cuvettes wer e operated at young trees in a forest clearing near ground level as we ll as at a mature tree species on top of the forest canopy, employing a specially designed tree top jungle raft (`Treetop Raft III, Dirigibl e version') placed on the canopy crown. The results show qualitative a nd quantitative disparities between different tree species as well as between individuals of the same species near ground level (young) and at the top of the canopy (mature). We found some correlations between photosynthetic CO2 assimilation and emission of sulfur compounds. Comp arison between measurements at the ground and at the canopy top show t hat the studied tree species adapts its photosynthetic CO2 assimilatio n in response to the climatic conditions at the canopy top. This is ac companied by a quantitative change in trace gas emission. Lower CO2 fi xation rates are accompanied by an increase in the emission of reduced sulfur compounds. We propose the increase of DMS emission at the cano py top to be explained by a potential demand of nitrogen in the foliag e resulting in an accumulation of sulfur.