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Effect of Light Level on Dinitrogen Fixation and Carbohydrate Distribution in Virginia Peanuts¹

The peanut (Arachis hypogaea L.) is an important grain legume world-wide, yet the N₂ fixation capabilities of this crop have received minimal attention. An experiment was conducted to study the effects of radiant flux on peanut growth, N₂ fixation, and the distribution of nonstructural carbohydrates among plant parts during vegetative and early-reproductive growth stages. Two Virginia-type cultivars, NC4 and NC6, were grown in controlled-environment chambers under average photon flux treatments of 230 and 650 µimol photon m^–2 s^–1. Plants grown under the higher irradiance accumulated three times more dry matter, fixed three times more N₂, and had greater reproductive potential than plants under the low irradiance. The greater fixation in plants under high light was attributed to an increased effective nodule mass in those plants and not to a greater efficiency of nodules to fix N₂. There were no significant cultivar differences for dry matter or N accumulation, although NC4 was always slightly higher than NC6. Concentrations of nonstructural carbohydrates in peanut tissues varied depending on the growth stage. The content of carbohydrates in root, stem, and leaf tissues was greater in high-light plants, compared with plants under low light. Within the high-light treatment, carbohydrate content was greatest in tissues of NC4 plants. Carbohydrate concentration in nodules was not significantly different between light treatments.

Key Words: Arachis hypogaea L. • Bradyrhizobium • Source-sink relations • Light

² Former research assistant (presently graduate research assistant, Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, St. Paul, MN 55108), professor, and former researcher (presently senior plant physiologist, Union Carbide Agric. Products Co., Research Triangle Park, NC 22709), Crop Science Dep., North Carolina State Univ., Raleigh, NC 27695-7620.

Received for publication March 22, 1985.