RELATIONSHIPS BETWEEN OZONE RESISTANCE AND CLIMATE IN EUROPEAN POPULATIONS OF PLANTAGO-MAJOR

The relative ozone resistance of 20 European and two American populati ons of Plantago major was examined, and relationships with climatic fa ctors at the source of the plant material were explored using data pro vided by participants in the ICP-Crops initiative (International Go-op erative Programme to Investigate the Effects of Air Pollutants and Oth er Stresses on Agricultural and Semi-Natural Vegetation). Plants grown from seed were exposed to either charcoal/Purafil(R) filtered air (CF < 5 nmol mol(-1) O-3) or CF+ozone (70 nmol mol(-1) O-3 7 h d(-1)) ove r a 2-wk period in controlled environment chambers, and effects on mea n plant relative growth rate (R) and allometric root/shoot growth (K) determined. Ozone resistance (R%) was calculated from (R-O3/R-CF)x100. Populations exhibited contrasting sensitivities to ozone, without the development of typical visible symptoms of injury. A positive relatio nship was found between relative ozone resistance and descriptors of t he ozone-climate at the site of seed collection for the year of, and t he 2 yr before, seed collection The best predictors of inherent ozone resistance were shown to be cumulative ozone exposure indices calculat ed according to current United Nations Economic Commission for Europe (UN-ECE) critical level guidelines for the pollutant (i.e. the accumul ated hourly average ozone exposure over a threshold level of 40 nmol m ol(-1) (AOT40) or 30 nmol mol(-1) (AOT30) calculated during daylight h ours for the consecutive 3-month period of the year experiencing the h ighest ozone concentrations). No relationships were found between ozon e resistance and climatic factors (temperature, precipitation, sunshin e hours, humidity) or the concentrations of other air pollutants (SO2, NO2, NO). These findings support the view that current ambient levels of ozone in many regions of Europe are high enough to promote evoluti on of resistance to the pollutant in native plant populations. The sig nificance of these findings to the debate over the establishment of se parate critical levels for the protection of natural and semi-natural vegetation is discussed.