Response of Soybean to Low Concentrations of Ozone: II. Effects on Growth, Biomass Allocation, and Flowering

Abstract

Abstract Soybean plants were subjected to ozone (O 3 ) and water stress to determine whether the two stresses interact to alter growth. Potted soybean ( Glycine max [L.] Merrill cv. Hodgson) plants were exposed to O 3 for 6.8 h daily in four controlled environment chambers. The air supply to the chambers was filtered, and constant amounts of O 3 were added: 0.01, 0.05, 0.09, or 0.13 µ L L −1 . Within each O 3 treatment, half of the plants were watered daily and half had water withheld 2 or 3 d per week. At 2‐week intervals plants were harvested and divided into leaves, stems, and roots. Exposure to increasing concentrations of O 3 resulted in a linear decline in growth, but did not influence the allocation of biomass to roots, stems, and leaves. Ozone also delayed the onset of flowering. Weekly water stress periods of 2 or 3 d duration significantly inhibited the growth of soybean but did not alter the allocation of biomass or delay the onset of flowering. Water stress acted to close stomates and reduce the effective O 3 dose which resulted in a reduced percent reduction in growth that could be attributed to O 3 stress.