The relation of H₂S release to SO₂ fumigation of lichens

Abstract

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 H₂S emission significantly in response to fumigation with 36 ppb SO₂. Parmelina tiliacea (L.) Hale and Cladina rangiferina (L.) Wigg. released significantly more H₂S (0·098±0·015 and 0·073±0·013 pmol H₂S 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 H₂S g⁻¹ d. wt s⁻¹, respectively). Release of H₂S in Hypogymnia physodes was enhanced by increasing SO₂ concentrations up to 72 ppb SO₂. No significant difference in H₂S emission in the dark vs. in the light was found. Generally, no correlation was found between photosynthetic activity and H₂S 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, H₂S-S release represents only 0·11–0·74% of SO₂-S uptake.