Reproductive Growth and Dry Matter Production of Glycine max (L.) Merr. in Response to Oxygen Concentration

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Abstract
Reproductive as well as vegetative parameters of mature soybean (Glycine max [L.] Merr. cv. Wye) plants grown in chambers in which the aerial portion was exposed to altered pO(2) during all or part of the growth cycle were measured. Oxygen concentration was found to be a key factor controlling all phases of reproductive development. Exposure to 5% O(2) from early seedling stage to senescence increased leaf, stem, and root dry weights and reduced seed yields when compared to 21% O(2); exposure to low O(2) during the vegetative growth stage from early seedling to mid-flowering arrested pod but not seed development; exposure from mid-flowering to mid-pod filling almost completely arrested seed but not pod development; exposure from mid-pod filling to senescence arrested seed development at the mid-filling stage.Exposures to 5% O(2) initiated at mid-flowering for 1, 2, 3, 5, 10, and 15 days had no effect on seed development when the exposure was up to 3 days and produced almost total arrest when the exposure was 10 or more days, suggesting reversibility. The requirement for O(2) in seed development is independent of CO(2) concentration with similar results produced by subambient O(2) combined with ambient CO(2), elevated CO(2) up to 2000 mul/l or depressed levels of CO(2) with the CO(2)/O(2) ratio as in air. An elevated O(2) atmosphere containing 40% O(2) and ambient or elevated CO(2) inhibited total growth but did not affect the balance of vegetative to reproductive growth.We conclude that an unknown reaction or process requiring at least atmospheric concentrations of O(2) but independent of CO(2) in contrast to photorespiration is necessary for optimization of all phases of reproductive growth and the effect is reversible for exposures of up to 3 days but not for exposures of 10 days or more. We propose that this O(2) phenomenon may be the result of a unique physical process or chemical reaction associated with translocation and accumulation of assimilates in reproductive structures.