EFFECTS OF OZONE CONCENTRATION ON GROWTH OF TOMATO AT VARIOUS LIGHT, AIR HUMIDITY AND CARBON-DIOXIDE LEVELS

The effect of ozone (O3) Concentration on the growth of Lycopersicon esculentum was studied at different photosynthetic photon flux densities (PPFD), relative air humidities (RH) and carbon dioxide (CO2) concentrations. Increasing the O3 concentration from < 10 to 85 nl l-1 for 6 h per day reduced the shoot dry weight 35% at 70% RH and 62% at 90% RH. Increasing the PPFD from 100 to 350-mu-mol m-2 s-1 significantly reduced the effect of O3 in one of two experiments. The most pronounced interaction between RH, PPFD and O3 was found on plant height. High O3 levels generally decreased plant height at low PPFD and had no, or a stimulating, effect at high PPFD. Raising the RH from 70 to 90% significantly increased the negative effect of O3 on height. Increasing the O3 concentration from < 10 to 65 nl l-1 significantly decreased plant height at low CO2 concentration (300-340-mu-l l-1), but small effects were found at high CO2 concentration (700-800-mu-l l-1).