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Photosynthetic Recovery of Peanuts to Defoliation at Various Growth Stages¹

This experiment was designed to study the response of peanut (Arachis hypogaea L.) canopy carbon dioxide exchange rate (CER) to degrees of foliage loss at different dates throughout the season. Peanut plots were manually defoliated 25, 50, and 75 % on different dates during the season for comparison with control plots (0% defoliation). Weekly, CER was measured on control plots and on plots which had been defoliated at different dates. Canopy CER was initially reduced 45 to 70% after 75 % defoliation reduced leaf area index (LAI) to about 1.0, but subsequent measurements revealed considerable CER recovery. Recovery of CER was related to two mechanisms, leaf area production and re-adaptation of previouslyshaded leaves to full sun.

The re-adaptation of leaves to full sun was most apparent from the inability of recently-defoliated canopies to use all the light they intercepted for CER, but after 1 to 2 weeks, efficiency of utilizing photosynthetically active radiation utilization improved without an increase in LAI. The re-adaptation process appeared to be related to increasing specific leaf weight. Recovery mechanisms, especially leaf production, diminished as the peanut plants matured and progressed into pod set and pod fill. Leaf area index increased after early defoliations; however, the rate of LAI increase paralleled that of control plots. For defoliations late in the season, leaf growth had ceased and was not stimulated as a result of defoliation.

Key Words: Arachis hypogaea L. • Modeling • Pest management • Defoliation • Photosynthesis • Carbon exchange

² Professor, Dep. Agric. Engineering, Univ. Fla., Gainesville.

³ Associate professor, and former graduate student, respectively, Dep. Ent. & Nemat., Univ. Fla., Gainesville.

⁴ Associate prof., Agron. Dep. Univ. Fla., Gainesville.

⁵ Associate prof., Dep. Agric. Engineering, Univ. Fla., Gainesville.

Received for publication March 25, 1981.