STUDIES ON THE TOLERANCE TO SULPHUR DIOXIDE OF GRASS POPULATIONS IN POLLUTED AREAS

Abstract

SummaryThe evolution of tolerance to sulphur dioxide (SO2) under differing degrees of selective pressure over the same period of time was investigated in Festuca rubra L. and Dactylis glomerata L. along a transect away from a point source (a smokeless fuel factory) in northern England. Populations of both species were sampled from eight sites along the 2 km transect, starting close to the factory. All populations were screened for relative sensitivity to acute injury, assessed as degree of leaf damage after fumigation with a high concentration of SO2. In the case of F. rubra, relative sensitivity to chronic injury was also determined, on the basis of changes in growth in response to a prolonged fumigation with a moderate concentration of SO2. Festuca rubra showed a clear cline of decreasing tolerance to acute injury with distance from the point source, but no such pattern was apparent for D. glomerata. Although the chronic fumigation produced reductions in various growth parameters for F. rubra, there was no clear indication of changes in tolerance along the transect. The pattern of evolution of acute SO2 tolerance in F. rubra is discussed in relation to the selective pressures imposed at different sites by combinations of high and low level emissions from the factory. The occurrence of tolerance to acute, but not chronic injury is in agreement with earlier work by the authors, which suggested that there was greater potential for the rapid evolution of the former at polluted sites.