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Plant Physiology 72:741-745 (1983)
© 1983 American Society of Plant Biologists

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Interaction of Combined Nitrogen with the Expression of Root-Associated Nitrogenase Activity in Grasses and with the Development of N2 Fixation in Soybean (Glycine max L. Merr.) 1

Peter van Berkum and Charles Sloger

United States Department of Agriculture, BARC-West, Beltsville, MD 20705, Nitrogen Fixation and Soybean Genetics Laboratory, BARC-West, Beltsville, MD 20705

Soluble root N concentrations of corn, sorghum, pearl millet, rice, wild rice, and soybeans were determined and related to measurements of nitrogenase activity and changes in availability of combined N to plants. In corn, sorghum, and pearl millet, applications of fertilizer N increased soluble root N concentrations, but root-associated nitrogenase activity was negligible in control and treated plants. Applications of NH4NO3 to rice increased the water soluble root N concentrations and inhibited root-associated nitrogenase activity. In wild rice, root-associated nitrogenase activity was absent during vegetative growth and developed at the reproductive growth stage. The soluble root N concentration decreased progressively as wild rice grew indicating that the availability of combined N in the root environment declined. Therefore, development of nitrogenase activity in wild rice is associated with the change in availability of combined N in the root environment. The development of nitrogenase activity in wild rice was probably not due to colonization of roots by N2-fixing bacteria because most probable numbers of recovery did not significantly vary throughout the plants' growth cycle. In field-grown soybeans with or without fertilizer N application, we also observed a relationship between a decrease in soluble root N concentration and the development of nitrogenase activity.

1 Supported by the United States Department of Agriculture, Agricultural Research Service, Nitrogen Fixation and Soybean Genetics Laboratory, Beltsville, MD, and the Agronomy Department, University of Maryland, College Park, MD, under Cooperative Agreement 58-32U4-3-370. Scientific article No. A-3390, contribution No. 6462 of the Maryland Agricultural Experiment Station, Department of Agronomy, College Park, MD 20742.






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ASPB Publications PLANT PHYSIOLOGY THE PLANT CELL
Copyright © 1983 by the American Society of Plant Biologists