Relative effects of elevated background ozone concentrations and peak episodes on senescence and above-ground growth in four populations of Anthoxanthum odoratum L

Four populations of Anthoxanthum odoratum from North Wales, UK, were exposed to the following combinations of mean background and peak concentrations of ozone for 12 weeks in solardomes: LL (14.3 ppb, 18.9 ppb, respectively), LH (14.8 ppb, 52.3 ppb), HL (28.9 ppb, 35.7 ppb) and HH (30.5 ppb, 72.1 ppb). Elevated ozone rapidly induced premature senescence, with effect increasing in the order: LL < LH < HL < HH. By week 11, the LH and HL treatments had induced similar amounts of whole plant senescence even though the AOT40₁₂ values (accumulated between 8am and 8pm) were very different at 10.6 ppm h and 4.1 ppm h, respectively. Overall, linear correlations between whole plant senescence were stronger for AOT0 than for AOT40. Intraspecific variation in the senescence response to the different profiles was observed after 11 weeks of exposure. Effects on growth and tillering were less pronounced than effects on senescence.