Impact Type: Direct exposure to pollutant
Some populations of broad leaved plantain (Plantago major) have been shown to be extremely sensitive to O3. The effect is to reduce growth and seed output. However, this species does not show visible symptoms so the effects cannot be seen without controlled experiments.
There is regional variation in the level of sensitivity of this species to O3, with a general south (more resistant) - north (less resistant) trend (Reiling & Davison, 1992, 1993; Pearson et al. 1996; Whitfield et al. 1997; Davison & Barnes 1998). Populations of this species change over a few years in response to changes in the environmental conditions (eg drought) and it has been shown that two populations near Sheffield increased in ozone resistance after 3-4 years with high ozone (Wolff et al., 2000). It is tempting to conclude that the south-north gradient and the change in resistance over time are due to ozone ie that there has been evolution of ozone resistance. However, as Reiling & Davison (1992) and Davison & Barnes (1998) have pointed out, it is very difficult to prove that this is the case. Other environmental factors such as water stress are just as likely to have been involved.
Most semi-natural vegetation is subject to water stress and/or nutrient limitation. There is evidence that both of these alter plant response to ozone (Davison & Barnes 1998).
|Critical Load/ Level|
No estimate available