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

ABSTRACT

Soybean plants were subjected to ozone (O₃) and water stress to determlne whether the two stresses interact to alter growth. Potted soybean (Glycine max [L.] Merrill cv. Hodgson) plants were exposed to O₃ for 6.8 h daily in four controlled environment chambers. The air supply to the chambers was filtered, and constant amounts of O₃ were added: 0.01, 0.05, 0.09, or 0.13 µL L^–1. Within each O₃ 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 O₃ 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 O₃ dose which resulted in a reduced percent reduction in growth that could be attributed to O₃ stress.

Key Words: air pollution • oxidant pollution • Glycine max • water stressed

¹ Supported by U.S. Environmental Protection Agency Grant no. DE-ASO2-77EV04368.A004.

² Assistant Scientist, Research Specialist, Research Specialist, and Assistant Professor, respectively, Boyce Thompson Inst., Tower Rd., Ithaca, NY 14853. Current address of 3rd and 4th authors: U.S. Rocky Mountain Forest and Range Exp. Stn., Fort Collins, CO, 80526; Dep. of Forestry, Univ. of Wisconsin, Madison, WI 53706, respectively.

Received for publication July 23, 1984.