Dactylis glomerata, Festuca rubra, Holcus lanatus, Lolium perenne and Phleum bertolonii were collected from one or more of three sites with differing pollution characteristics in the north of England, and screened for tolerance to both acute and chronic sulphur dioxide injury in comparison with either bred cultivars or individuals of the same species collected from clean areas. Selection for tolerance was detected in all species and at all sites, suggesting that this is widespread in the field.
Differential response to chronic injury was manifested as effects on senescence, dry matter production, and/or partition of assimilate between roots and shoots. No correlation was found between the degree of acute and chronic injury at either the intraspecific or interspecific levels, which may indicate independent physiological mechanisms for these. Tolerance may evolve within 17 to 25 years. The significance of the evolution of SO2 tolerance for grasslands at polluted sites is discussed.