SUMMARYNet photosynthesis of 5-\veeU-old tomato plants (Lycopersicon lycoperstcuni L. cv. Abunda), was measured m clean air or with NC) fumigation, for five consecutive days under simulated winter fjlasshovise conditions: temperature 22 °C VPD 0'4 kPa, irradiance 30 W m ' and daylength 8-9 h. NO concentrations applied were 0 or 1 //I 1"' in combination with CO.j concentrations of 350 or 1000//I VK A reduction in net photosynthesis due to NO became apparent on the third day of measurement. On the fifth day this reduction was 38",, of the control at 350/(11 ' COj and 24",, at 1000//11 ' CO.^. The increase in photosynthesis due to CO., enrichment was initially 40 "" ; this effect was strongly reduced after 5 d in the presence of NO. Plants did not recover in the dark after the daily fumigation treatment, the le\-el to which photosynthesis was' reduced at the end of the day being the level at which it started tl>e next day. The decresise in photosynthesis could not be explained by an increased stomatal resistance, and the plants did not show visible symptoms of injury. Practical implications of the results are discussed.

SUMMARYPopulations of Silene cucubalus Wib. which were sensitive or tolerant to heavy metals or sulphur dioxide, were grown in zinc-or copper-supplemented soil and were exposed to mixtures of SOg, O3 and NO2 in low concentrations for a period of 12 weeks. Fumigations were applied only during elevated ambient concentrations of ozone. Growth during fumigations was reduced, but flower production was significantly higher in metal-tolerant populations when grown m soil supplemented with their specific metal. Flowers were hand-pollinated when plants were exposed to at least 60 /*g m'^ O3, 40 fig m'^ SO^ and 60 {ig m'^ NO^. Although the number of seeds and individual seed weight were significantly influenced by heavy metals and/or air pollutants, it appeared that flower production has the greatest efTect on potential sexual reproduction. Plants whicb have evolved resistance to pollution express optimal reproductive capacity when grown in soil most resembling their native soil. The interpretation and comparison of results gamed under experimental conditions are discussed with respect to field observations and effects of pollutant/species combinations.

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