Abstract: | The effects of SO2 on some growth and quality characteristicsof lucerne (Medicago sativa L.) were investigated by exposingplants to mean SO2 concentrations of 215, 78 or 2.8 µgm3 in open-top chambers for 166 d. Plants exposed to215 µg m3 had significantly lower shoot and rootweights compared with plants exposed to 78 µg m3,but not compared with control plants. Exposure to 215 or 78µg m 3 increased the plant shoot: root ratio, buthad no effect on leaf area. During the middle of the fumigationperiod, relative growth rate and net assimilation rate werehighest in plants exposed to 215 fig m, but these later fellbelow control values, and plants exposed to 78 µg m3had the highest relative growth rate and net assimilation rate.As the duration of exposure increased, an initial SO2-inducedstimulation of growth may have developed to toxicity at thehighest SO2 exposure. Exposure to SO2 depressed L-ascorbic acid concentrations inleaves, had no effect on foliar protein or starch concentrations,and increased the specific energy of shoots and plant sulphurconcentrations. The effect of SO2 on L-ascorbic acid concentrationsmay suggest a mechanism for reduced freezing tolerance of plantsafter exposure to SO2. Key words: SO2, Medicago sativa L., Growth |