Drought and Flooding Effects on N2 Fixation, Water Relations, and Diffusive Resistance of Soybean1
- J. M. Bennett and
- S. L. Albrecht2
Symbiotic N2 fixation depends on an interaction between bacteria and a host plant and is affected by both aerial and below-ground environments. The specific objectives of this study were to determine the effects of drought and flooding on nitrogenase activity of soybeans [Glycine mar (L.) Merr.] growing in sandy soils and to relate the changes in activity to the availability of soil water and to observed stress responses of the shoot. Three greenhouse experiments were conducted in which plants were subjected to drought or flooding for 14 days. During the stress periods, midday measurements of gravimetric soil water content, leaf water potential (ΨL) leaf diffusive resistance, nodule water potential (Ψmod) and nitrogenase activity were collected. Flooding of soybeans for 14 days had little effect on (ΨL), leaf diffusive resistance, or (Ψmod). Although some initial leaf yellowing and structural alterations of the root and crown were apparent in the flooded plants, the nitrogenase activities of nodules after removal from the flooded environment were similar to those of the controls by the termination of the experiment. Data from drought stressed plants indicated a very sensitive response of nitrogenase activity to reductions in (Ψmod) and further suggest that nodules surrounded by dry soil may desiccate to water potentials lower than those observed for leaf tissue. Even after water deficits reduced midday N2 fixation to near zero for several days, rewatering restored activities to values equal to or above those of well-watered plants. Reduced rates of nitrogenase activity were observed as (ΨL) decreased and diffusive resistance increased.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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