Changes in Growth and Quality Characteristics of Lucerne (Medicago sativaL.) in Response to Sulphur Dioxide Exposure under Field Conditions

Abstract

The effects of SO2 on some growth and quality characteristics of lucerne (Medicago sativa L.) were investigated by exposing plants to mean SO2 concentrations of 215, 78 or 2.8 μg m−3 in open-top chambers for 166 d. Plants exposed to 215 μg m−3 had significantly lower shoot and root weights compared with plants exposed to 78 μg m−3, but not compared with control plants. Exposure to 215 or 78 μg m −3 increased the plant shoot: root ratio, but had no effect on leaf area. During the middle of the fumigation period, relative growth rate and net assimilation rate were highest in plants exposed to 215 fig m, but these later fell below control values, and plants exposed to 78 μg m−3 had the highest relative growth rate and net assimilation rate. As the duration of exposure increased, an initial SO2-induced stimulation of growth may have developed to toxicity at the highest SO2 exposure. Exposure to SO2 depressed L-ascorbic acid concentrations in leaves, had no effect on foliar protein or starch concentrations, and increased the specific energy of shoots and plant sulphur concentrations. The effect of SO2 on L-ascorbic acid concentrations may suggest a mechanism for reduced freezing tolerance of plants after exposure to SO2.