An integrating sphere for the rapid nondestructive estimation of whole-plant chlorophyll content

Abstract

The chlorophyll contents of seedlings of several plant species were estimated from the voltages emitted by a photocell before and after the insertion of the shoot systems into a 61-cm integrating sphere. Red light of 675-nm wavelength was projected into the sphere for selective absorption by chlorophyll, as shown by an absorption spectrum, and the readout was calibrated against total extracted chlorophyll. The species and thus the morphology of the plant were of no significant consequence. The absorbance by chlorophyll in plants obeyed Beer's law up to a content of about 60 mg chlorophyll; however, over a wider range the calibration curve for absorbance, like that for absorptance, was best fitted by a quadratic equation which gave a coefficient of determination of 98% and a standard error of estimate for chlorophyll of 2 mg. A band width of 4 mg chlorophyll was obtained between the 95% confidence limits for chlorophyll as a function of absorbance of plants that contained less than 20 mg chlorophyll. A similar 4-mg confidence belt for chlorophyll on absorptance applied through the range of about 5 to 45 mg chlorophyll in plants. A usable linear relation was obtained between chlorophyll content and the ratio of the scattered light not absorbed at 750 nm to that at 675 nm.