Influence of Ozone, Sulfur Dioxide, and Salinity on Leaf Injury, Stomatal Resistance, Growth, and Chemical Composition of Bean Plants

Bean plants (Phaseolus vulgaris L. var. ‘Bush Blue Lake no. 274’), growing in half-strength Hoagland solutions modified to provide three salinity levels of −40, −240, and −440 kPa, were exposed four times to 390 µg m⁻³ O₃, 520 µg m⁻³ SO₂, and 390 µg m⁻³ O₃ + 520 µg m⁻³ SO₂. Fumigations were performed between 0900 and 1600 hours. Environmental conditions during fumigation were: temperature 25–35° C, relative humidity 43–51%, and photon flux density 200–600 µmol m⁻² sec⁻¹. Plants fumigated with SO₂ alone showed no injury. Primary leaves of O₃-treated plants were injured more than those of plants fumigated with the combination of O₃ and SO₂. Pollutant injury to leaves decreased as salinity increased. Stomatal resistance on the abaxial surface of primary leaves of SO₂, and especially of (O₃ + SO₂)-treated plants, increased sharply during fumigations, and returned to prefumigation levels the next day. Stomatal resistances of O₃-treated plants were similar to nonfumigated plants during the first phase of the experiment, but after the last fumigation, this resistance returned to essentially normal only in plants growing at the highest salinity level. Plant growth was suppressed by increased salinity. Root growth on O₃- and (O₃ + SO₂)-treated plants was reduced at all salinity levels. As salinity increased, plants accumulated Cl and Ca. Sodium increased in stems and roots, and decreased in leaves of plants grown in high Na-nutrient solutions. Plants fumigated with SO₂ and (O₃ + SO₂) had higher S content in roots than nonfumigated and O₃-treated plants. The highest S content in leaves was found in SO₂-treated plants at the −40 kPa salinity level. Accumulation of Ca in leaves and of Mg in roots was lowest in plants fumigated with O₃ alone and (O₃ + SO₂). Plants fumigated with O₃ alone and (O₃ + SO₂) accumulated more K in stems and leaves, and more Fe in roots and leaves, compared with nonfumigated and SO₂-treated plants. The O₃ and (O₃ + SO₂) effects on mineral content of the plants was suppressed by salinity, and the pollutant treatments had no statistically significant effect on mineral content of plants growing at −440 kPa salinity.