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Effect of Moisture Stress on Photosynthesis and Some Related Physiological Characteristics in Peanut¹

Two experiments were conducted to assess the effects of water stress on net photosynthesis (Pn) in peanut (Arachis hypogaea L.), since indications from earlier reports were that peanut photosynthesis might be less affected by water stress than in other crop species. Three genotypes of peanut were grown in pots in the greenhouse in 1973 (Experiment 1) and two were grown outside pots in 1974 (Experiment 2). Soybean [Glycine max (L.) Merr.] was included in Exp. 2 for comparison. Net photosynthesis and transpiration were measured on single leaves during a 5 or 6-day drying cycle with assimilation chambers and relative leaf water content (RLWC) was determined by floating leaf discs on water. Diffusive resistance was calculated from transpiration data and also measured with a diffusion porometer. Water potential was determined on leaves and immature pods on the last 2 days of Exp. 2. Decreases in Pn of stressed plants during the drying cycle were closely related to decreases in RLWC and transpiration. The relationship between Pn and RLWCw as similar for peanut and soybean in Exp. 2. The diffusive resistance determined with a porometer or from transpiration varied between 0.5 and 2.5 sec cm^-1 for control plants, while the diffusive resistance of stressed plants reached maximum values of 18 to 20 sec cm^-1 in Exp. 1 and between 30 and 35 sec cm^-1 for peanut and soybean in Exp. 2. No differences appeared among genotypes of peanut in the response of Pn to water stress. Water potential of immature pods was equal to, or slightly higher than that of leaves at the end of Exp. 2. Comparison of the data for peanut with that from soybean and also with published data indicates that Pn of peanut is controlled by water stress in a manner quantatively similar to that of other crop species.

Key Words: Relative leaf water content • Diffusive resistance • Water potential • Soybean • Arachis hypogaea L.

² Former research assistant, professor, and assistant professor of agronomy, respectively.

Received for publication December 20, 1975.