Effects of the bisulphite ion on growth and photosynthesis in Sphagnum cuspidatum Hoffm

Shoots of Sphagnum cuspidatum Hoffm. were collected from two sites: one, a relatively unpolluted site in N. Wales, remote from pollution sources and the other, a grossly polluted site in the South Pennines.* Material from both sites was grown in the laboratory and exposed to artificial rainwater solution with and without bisulphite (HSO₃ ) amendment (0.1 mM). Effects of exposure to HSO₃ for up to 21 days on growth, photosynthesis, chlorophyll a fluorescence and chlorophyll concentrations were studied in the two Sphagnum populations. Application of HSO₃ produced significantly less than maximum growth in Sphagnum from both sites. This effect was far greater, however, in the material from the unpolluted Welsh site. Photosynthesis in the Welsh material treated with HSO₃ decreased steadily with time; after 21 days of exposure, photosynthetic oxygen evolution had ceased. This decrease was accompanied by a decrease in fluorescence quenching (as [(P - T)/P]), suggesting a gradual loss of water-splitting activity. In contrast, HSO₃ initially stimulated photosynthesis in Sphagnum from the polluted site. Chlorophyll concentration was decreased in Spliagmtm from both sites in the presence of HSO₃ Possible mechanisms of tolerance to HSO₃ are discussed.