The relationship between extracellular metal accumulation and bisulphite tolerance in Sphagnum cuspidatum Hoffm

Sphagnum cuspidatum Hoffm. was collected from a remote site in N. Wales, and a polluted site in the S. Pennines. When added to artificial rainwater solution, HSO₃ ^- was oxidized to SO₄ ^2- . The rate at which this oxidation occurred was modified differentially by the mosses from the two sites. S. cuspidatum from the S. Pennines promoted a rapid oxidation rate and disappearance of HSO₃ ^- was complete in 6 h. S. cuspidatum from N. Wales, on the other hand, achieved a very slow oxidation rate and HSO₃ ^- persisted in solution for more than 24 h. Prolonged exposure to HSO₃ ^- in the Welsh material caused damage to, and eventual death of, this material but not of the S. Pennine moss. The rates of HSO₃ ^- oxidation promoted by the mosses from the two sites appear to be related to the concentration of the transition metal ions, Fe(III), Mn(II), and Cu(II), present on the cell-wall cation-exchange sites. These metals, particularly Fe, present on the surface of the S. Pennine material catalysed a rapid chemical oxidation of HSO₃ ^- to SO₄ ^2- . The increased levels of transition metals associated with the S. Pennine moss originate in the peat as a legacy of past pollution events at this site. Levels of Fe were approximately 100 times greater than those for Mn or Cu and 5-10 times higher on the S. Pennine moss than on that from N. Wales. Removal of these metal ions (using EDTA) from the surface of the S. Pennine material removed the HSO₃ ^- oxidizing ability of the moss, leading eventually to cell death. The ability to withstand high levels of HSO₃ ^- was conferred upon the Welsh moss by supplying Fe(m) in artificial rainwater solution under laboratory conditions. Transplanting Sphagnum from the Welsh to the S. Pennine site gave rise to a similar response. Nomenclature of mosses follows Smith (1978).