A rapid change in ozone resistance of Plantago major after summers with high ozone concentrations

Abstract

S L' M M A R YOzone concentrations in Britain vary greatly from year to year. In the mid-1980s they were relatively low but in 1989 and 1990 the numher of hours when concentrations exceeded 60 nl I"-* was 3^ times greater than in the preceding 2 yr. Previous experiments suggested that this might have resulted in an increase in ozone resistance of Plantago major L. populations, so a comparison was made of seed-grown plants collected from the same three sites in Derbyshire/South Yorkshire in the 1980s and 1991. Ozone resistance was measured by exposure to charcoalfiltered air or air containing 70 nl 1 ' O^ (7 h d"^) and expressed as R^o-the mean relative grow-th rate in ozone expressed as a "o of that in charcoal-tiltered air. Ozone resistance changed significantly in two of the populations (ISP and Totley) hetween the years 1985 and 1991. There was no significant change in the resistance of the Scaftworth population between 1988 and 1991 when expressed as R"(, hut there were significant physiological differences between the collections. The changes in R% were accompanied by differences in the response of the stomata to ozone and in effects on dark respiration, hut not in assimilatory capacity. This is the first report of a change in ozone resistance in populations over a short period of time. It is not known if the 1991 plants were the descendants of the 1985/88 plants or whether there had been an invasion by new genotypes from outside the area. The role of other environmental factors in determining ozone resistance, and the implications of the data for the definition and mapping of critical levels are both discussed. It is predicted that if the reported changes were caused by ozone, the region where future changes in ozone resistance are most likely to occur is that between the Midlands and the north of England.

Influence of plant age on ozone resistance in Plantago major

“…Secondly, because reproductive performance is most affected by O $ during the initial stages of flowering, exposure to O $ at this stage of development would be expected to result in particularly marked effects on seed production which would contribute to the loss of sensitive individuals from within a population, thereby promoting the selection of individuals resistant to the pollutant. Indeed, there is evidence for the occurrence of such evolutionary changes within populations of P. major in the field (Reiling & Davison, 1992 b ;Davison & Reiling, 1995 ;Ashmore & Davison, 1996 ;Lyons et al, 1997). There is, however, a clear need to verify the findings of this chamber-based investigation in the field.…”

“…Attention is drawn to the timing of O $ episodes in the field in relation to plant age and prior O $ history within the context of the available evidence for the evolution of O $ resistance in this species (Reiling & Davison 1992 b ;Davison & Reiling, 1995 ;Ashmore & Davison, 1996 ;Lyons et al, 1997).…”

Effects of Air Pollution on Ecosystems and Biological Diversity in the Eastern United States

“…Because species vary in their sensitivity, O 3 can shift the competitive balance in plant communities to the detriment of sensitive species (Miller and McBride 1999). Further, because individuals of a given species vary in their sensitivity, O 3 exposure can cause changes in genetic structure of populations, reducing or eliminating sensitive genotypes (Taylor et al 1991;Davison & Reiling 1995).…”

Trends and rates of microevolution in plants

“…Many initially susceptible populations of crop weeds evolve resistance to the herbicides used to control them within as few as two generations (Heap, 1997;Powles et aI., 1998;Mallory-Smith, Hendrickson & Mueller-Warrant, 1999). Many plant species have evolved in response to recent environmental changes, such as ozone pollution and atmospheric C02 increase (Davison & Reiling, 1995;Ward et aI., 2000).…”