The relation of H₂ S release to SO₂ , fumigation of lichens

Hydrogen sulphide emission in lichens as a response to low concentration SO₂ , fumigation was investigated. In an open flow-through system several lichen species were fumigated with 36 ppb SO₂ , Two species were also fumigated with higher concentrations (72, 119, 122 and 198 ppb SO₂ ,). Hydrogen sulphide emission was monitored concurrently by cryogenic trapping and analysis with gas chromatography. All tested species increased H, S emission significantly in response to fumigation with 36 ppb SO₂ . Parmelina tiliacea (L.) Hale and Cladina rangiferina (L.) Wigg. released significantly more H₂ S (0.098±0.015 and 0.073±0.013 pmol H₂ S g^-1 d. wt s^-1 , respectively) than Parmelina quercina (Ach.) Hale, Ramalina menziesii Tayl. and Parmelia sulcata Tayl. (0.028 ± 0.01, 0.025±0.014 and 0.023±0.013 pmol H₂ S g^-1 d. wt s^-1 , respectively). Release of H₂ S in Hypogymnia physodes was enhanced by increasing SO₂ concentrations up to 72 ppb SO₂ . No significant difference in H₂ S emission in the dark vs. in the light was found. Generally, no correlation was found between photosynthetic activity and H₂ S emission for the tested species. Uptake of SO₂ was similar for all species, at 24.7 ± 5.6 pmol SO₂ g^-1 d. wt s^-1 in 36 ppb SO₂ and increasing at greater SO₂ concentrations. Therefore, H₂ S-S release represents only 0.11-0.74% of SO₂ -S uptake.