Canopy Photosynthesis and Transpiration of Cotton as Affected by Leaf Type1

Abstract

Cotton (Gossypium hirsutum L.) plants with okra or superokra leaves have several agronomic characteristics which could make them better adapted to narrow‐row culture than plants with normal leaves. This study was conducted to investigate the effect of these leaf types on canopy photosynthesis and transpiration of narrow‐row cotton. A portable, open‐chamber system was used in plant communities grown at high and low densities. In 1973 the three leaf types (normal, okra, and superokra) had dissimilar genetic background with the okra and superokra leaf lines being similar in appearance and leaf area. Maximum leaf area index (LAI) these canopies was approximately 2.8 compared to 4.6 for normal leaf plants. Near‐isogenic lines were used in 1974. Although morphologically distinctive, the okra and normal isolines had maximum LAIs of approximately 5.2, compared with 3.5 for the superokra leaf isoline. Apparent photosynthesis was positively associated with LAI, although correlation coefficients were low (0.23 to 0.54). Plant population had little effect on canopy photosynthesis. When data were averaged across populations, normal leaf plants had CO2 exchange rates 20 and 29% higher than superokra leaf plants in 1973 and 1974, respectively. Okra leaf plants were intermediate. Leaf type effects on transpiration were small and inconsistent during the 2 years. Although differences in photosynthesis to transpiration ratios statistically nonsignificant, the trend was normal>okra> superokra. Thus, the okra leaf types do not appear to be associated with improved efficiency of water use.