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Does UV-B radiation alter water use efficiency in soybean?
Sullivan, Joe1, Gitz, Dennis1, Liu-Gitz, Lan2, 1 2
ABSTRACT- Interactions between UV-B radiation and drought stress have been observed but the underlying mechanisms have not been thoroughly investigated. We evaluated whether UV-B induced changes in epidermal development such as reduced stomatal density might result in increased water use efficiency in soybean. Soybean (Glycine max L. cultivars Essex, Williams, OX921 and OX922) plants were grown in both glasshouse and field studies with and without supplemental UV-B radiation. In the glasshouse the levels of UV-B were either 0 or 13 kJ m-2 biologically effective radiation and in the field UV-B levels were either near ambient or reduced by about 80% using polyester filters. In virtually all cases UV-B radiation increased phenolic content of leaves and reduced leaf area. Adaxial stomatal density was reduced in all cultivars but abaxial stomatal density was only reduced in the OX922 cultivar in the greenhouse. In the field, however, UV reduction lowered stomatal density in the OX921 cultivar. Stomatal conductance was reduced in concert with stomatal density, as was internal CO2 concentration (Ci). Instantaneous water use efficiency was increased in Essex, Williams and OX922 and stable carbon isotope analysis showed similar trends in long-term water use efficiency. These results are consistent with the notion that UV-B exerts a photomorphogenic influence on soybean development that results in improved water use efficiency and could improve drought tolerance in some cultivars.
KEY WORDS: UV-B radiation, water use efficiency, drought tolerance, soybean