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SUMMARYIn three separate experiments, the response of three populations of Agrostis capillaris L., Nardus stricta L., and Lolium perenne L., from areas differing in ambient air pollution concentrations, were examined in experimental fumigations using SO.^, O.,, NO, and NH.,. Growth of .4. capillaris generally increased following the fumigations, except at the highest pollutant concentrations (120/(g m •' (),,, alone or combined with 150//g m •' SO, and 35 //g m -NO.j). (Jrow-th of each population of A^. stricta was stimulated by the SO, and NH., combination, but vvas significantly increased only in the poptilations originating from the ri-iost heavily polluted of the three areas. The growth of L. perenne was not inhibited by any air pollutant or combination of pollutants. f3espite a low grow-th rate in clean air and a large ati-iount of within-population variation, hiomass production was significantly stimulated by the highest pollutant mixture.1 he response of each species to the experimental treatn-ients depended in part on the location from which it originated. This site-dependent (population) response differed between species, suggesting that the selective processes induced by these air pollutant concentrations were insufficient for a clear-cut adaptation to gaseous air pollutants.

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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