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

Abstract

S ummary Genotypes of Lolium perenne, Festuca rubra, Dactylis glomerata and Holcus lanatus which appeared to be differentially sensitive to acute or chronic SO 2 injury were compared in various morphological and physiological studies to examine some possible mechanisms of tolerance. Stomatal number and size showed no relationship with tolerance, but stomatal resistance in clean air showed a relationship with intra‐ and interspecific differences in tolerance to acute injury. Also, acute doses of SO 2 increased stomatal resistance in tolerant, but not in sensitive species. Membrane permeability was increased by acute doses of SO 2 , but there were no differential effects which could be related to tolerance. Uptake of 14 CO 2 by leaf segments in buffered solution was reduced in the presence of sulphite to a greater extent in genotypes of Lolium perenne sensitive to chronic injury. Prefumigation for 13 months with a low concentration of SO 2 increased the sensitivity to sulphite, especially in the sensitive genotypes. The species tolerant of acute SO 2 injury, Dactylis glomerata and Holcus lanatus , had lower rates of 14 CO 2 fixation than sensitive species, and were affected less by sulphite. There were no relationships between prefumigation or sensitivity to chronic injury and the uptake or oxidation of sulphite in three Lolium perenne genotypes. Species sensitive to acute injury absorbed more 35 SO 2 than tolerant species. Oxidation of the absorbed radioactivity was fastest in the most tolerant and slowest in the least tolerant species. It is concluded that many of the differential responses to acute injury can be explained by avoidance mechanisms. Some potential mechanisms of tolerance to chronic injury are discussed.