| ||||||||||||||||||||
Ions ward off acid attacks
In SO2-polluted environments mosses and lichens growing on limestone buildings often fare better than those growing on other substrata. Similarly, some terricolous (soil-growing) mosses are confined to calcareous soils in polluted areas, but are more widespread in non-polluted areas. It has been suggested that ions taken up from calcareous soils may alleviate the effects of SO2. However, this does not account for the survival of calcifuge species in SO2-polluted areas. Thus, Bharali and Bates (Imperial College, University of London, pp. 337-343) investigated the role of soil cations in acid and alkaline soils in the response of mosses to bisulfite (HSO3, the predominant form of SO2 at acid pH. Pleurozium scheberi, a strict calcifuge and Rhytidiadelphus triquetrus, a facultative calcicole, were the two species used. In both there was an immediate and very marked depression of the rate of photosynthesis after the application of bisulfite, especially at more acid pHs. However, photosynthesis started to recover after 2 h and in the less severe instances of inhibition the photosynthetic rate approached that of control plants after about 10 h. Surprisingly, shoot elongation growth was little affected by weekly applications of sodium bisulfite except in P. scheberi, the strict calcifuge, when grown on calcareous soils. The recovery of the rate of photosynthesis and the lack of a significant effect of bisulfite on shoot growth are consistent with earlier suggestions that ions taken up from the soil may ameliorate the effects of bisulfite. Further evidence comes from experiments in which the mosses were pre-treated before application of the bisulfite: FeCl3 ameliorated the photosynthetic inhibition in both species and CaCl2 also did so in R. triquetrus, the facultative calcicole. The reasons for the amelioration are not clear (although some are proposed by the authors), but it is clear that these results pave the way for further interesting work.
Professor J. A. BryantUniversity of Exeter, UK
j.a.bryant{at}exeter.ac.uk
| ||||||||||||||||||||