Studies on the Effect of Sulphur Dioxide on Perennial Ryegrass (Lolium perenneL.) II. EVOLUTION OF SULPHUR DIOXIDE TOLERANCE

The response to S02 fumigation was examined in long-established perennial ryegrass populations from the same climatic region, which had experienced widely different ambient S02 concentrations. The results provide strong evidence of the evolution of S02 tolerance in populations from the high S02 areas. Populations from these areas exhibited greater tolerance to S02 and showed reduced clonal variability in response. Furthermore, the degree of tolerance exhibited appeared to depend on the severity of S02 pollution experienced by the populations in the field. INTRODUCTION One example of the manner in which man's activities can cause evolutionary change in plant populations over relatively short periods of time is the evolution of tolerance to heavy metals in plants (Bradshaw, 1975). Differential responses to S02 fumigation dependent on the site of origin of plant populations have been shown by Bell and Clough (1973), Horsman and Wellburn (1977), and Taylor and Murdy (1975). Recent research has shown that S02 can markedly affect the growth of peren nial ryegrass (see discussion in previous paper). Hence in areas which have experi enced a long history of high ambient S02 concentrations, ryegrass populations may have evolved some degree of tolerance, providing that sufficient inherent genetic variability in response to S02 existed within the population. The findings of Bell and Clough (1973) strongly suggest that the indigenous ryegrass population at Helmshore (24 km north of Manchester) has evolved tolerance to S02. It was not known, however, to what extent the response of the two ryegrass clones selected from Helmshore reflected an overall population response. Since urban areas of Liverpool have experienced consistently higher S02 concentrations than Helmshore (Anon., 1972) any evolution of tolerance to S02 may be more evident in ryegrass populations from Liverpool than Helmshore. We have therefore investigated (a) overall population responses and (b) variability in 1 Present address: School of Botany, University of Melbourne, Australia. 2 Present address: Central Electricity Research Laboratory, Leatherhead, Surrey. This content downloaded from 207.46.13.73 on Thu, 11 Aug 2016 04:46:37 UTC All use subject to http://about.jstor.org/terms 496 Horsman, Roberts, and Bradshaw—Sulphur Dioxide Effects on Ryegrass genotype response to S02 in long established ryegrass populations from Helm shore, urban areas of Liverpool (high S02), and the Wirral peninsula (low S02 area, 10-20 km south-west of Liverpool). MATERIALS AND METHODS Clones of ryegrass were collected at random from the sites shown in Table 1. The populations from Newsham, Wavertree, West Kirby, and Birkenhead were collected from the lime lines of tennis courts (pH 5-5-6-5). This was necessary since, in Liverpool, these were the only areas of parkland where substantial perennial ryegrass populations survive due to the general acidification of the rest of the parkland, presumably as a result of the high S02 concentrations they have experienced. This means that although the populations have experienced widely different ambient S02 concentrations the climate, soil, and management conditions have been comparable. Table 1. Origin of ryegrass populations and typical winter mean S02 con centrations (jug m~3) found at these sites Site Late 1950s early 1960s Helmshore 100-140 80 Liverpool Newsham 600-700 200 Wavertree 600-700 200 West Kirby 60-80 35 Wirral Birkenhead 80 40 University 60-80 40 Botanic Gardens, Ness The ryegrass clones were individually identified, planted in a John Innes compost (pH 6-0), and grown in a greenhouse at the University Botanic Gardens, Ness, for at least 6 months. Experi mental design and procedures were as described in the previous paper.