EXCHANGE OF REDUCED SULFUR GASES BETWEEN LICHENS AND THE ATMOSPHERE

Fourteen lichens, 10 green algal lichens and four cyanolichens, as well as a cyanobacterium emitted significant quantities of H2S (0.01-0.04 pmol g dw-1 s-1) and DMS (0.005-0.025 pmol g dw-1 s-1), but were sinks for COS (0.0 1 5-0.14 pmol g dw-1 s-1). In contrast, exchange of CH3SH and CS2 were sporatic and inconsistent. Although some interspecific variation occurred for the first three gases, exchange rates were relatively uniform and were not influenced by irradiance conditions. In contrast to DMS and H2S emission, COS uptake was strongly influenced by degree of thallus hydration. Because lichen dominated systems cover extensive terrestrial habitats, COS uptake is potentially important in the world's sulfur budget.