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Abstract
A new type of chlorophyll fluorometer was evaluated, and a novel technique was developed for accurately estimating thylakoid electron transport rates with this instrument. Then, combined measurements of leaf gas exchange and chlorophyll fluorescence were used to investigate the effects of water stress on photosynthesis of cotton leaves. A computer-automated lysimeter was used to impose distinct levels of water stress on potted cotton plants. Under mild water stress, limitations to photosynthesis were entirely attributable to stomatal closure, which reduced leaf internal CO2 concentrations. Under moderate or severe water stress, non-stomatal limitations to photosynthesis were also observed; these were evident as a reduction in the net CO2 assimilation rate for a given CO2 concentration within the chloroplast. After re-watering severely water stressed plants, stomatal limitations to photosynthesis returned to control levels within 24 hours. However, non-stomatal limitations remained elevated even 48 hours after re-watering, indicating lasting injury to the photosynthetic apparatus.