Environmental stresses on plants are a constant threat to crop production in nearly all world areas. Stress from drought and temperature extremes are particularly serious and are an annual occurrence in the Great Plains of the United States. As water supplies for irrigation dwindle, and energy costs increase, an increased acreage must be diverted to dryland production. Because of the decreasing water table in the Ogallala aquifer, increases in production must come from plant germplasm with increased water-use-efficiencies. One strategy to increase the water-use-efficiency would be to increase in the photosynthetic light quanta conversion during stress, thereby providing more photosynthate for the limited amount of water.

This study was undertaken to determine if chlorophyll a fluorescence transients would provide a rapid, nondestructive technique for analysis of the adaptation of photosynthetic light quanta conversion during severe water stress. Cotton Strain, Lubbock Dwarf, was planted in an Amarillo loam soil which was irrigated to field capacity prior to planting. A rainout shelter was used to keep water off the plots during the growing season, and selected rows were irrigated throughout the experiment with a drip irrigation system. Measurements on chlorophyll fluorescence, plant growth, plant water status, and photosynthesis were made on selected dates during the growing season.