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.
Keywords: Lichens; detoxification; hydrogen sulphide; sulphur dioxide.