Effects of air pollutants on plants

Ozone is the most important air pollutant affecting plants in Switzerland a nd in many other regions of NW-Europe. Critical levels set by the UN/ECE to protect plants are exceeded over extended areas, but there is increasing e vidence that selection for ozone tolerance can take place in response to in tensive ozone stress. Effects of ozone, including visible injury, or long-t erm changes in growth, biomass allocation, yield, reproduction, competitive ness, and vitality, depend on the dose of ozone absorbed by the plant. In o rder to assess the ozone risk for vegetation, it is thus necessary to devel op dynamic models for flux-effect relationships which take into account the modifying influence of environmental mental factors.