Effect of Petroleum Oil Spray on Photosynthesis and Respiration in Citrus Leaves

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Abstract
The photosynthesis and respiration of disk samples from leaves of Washington navel orange and Eureka lemon were studied by the use of a Warburg respirometer modified to provide illumination from a bank of fluorescent lamps placed below the flasks. Both processes were studied under a constant CO2 tension maintained by means of a diethanolamine-carbonate buffer system. The application of petroleum oil emulsions in amts. approximating those used as insecticides on citrus was found to depress the rate of photosynthesis in leaves of both spp. The max. depression of photosynthesis in the orange leaves was about 70%, while in lemon leaves it amounted to more than 80%. Some inhibition of the process persisted for as long as determinations were made (59 days). A corresponding, but smaller, decrease in respiration was found in the oil-treated leaves.