Leaf level detection of solar induced chlorophyll fluorescence by means of a subnanometer resolution spectroradiometer

A leaf level investigation on the spectral signature of Phaseolus vulgaris was undertaken by using a very high spectral resolution spectroradiometer featuring full width at half maximum of 0.06 nm and spectral range of 635.5–802.5 nm. High spectral resolution allows detection of leaf reflected and emitted radiance fields in two narrow absorption bands at 687 and 760 nm, respectively, where solar irradiance is strongly reduced owing to molecular oxygen absorption of the terrestrial atmosphere. The flux emitted due to chlorophyll fluorescence was measured using the Fraunhofer line depth principle by spectrally modelling the signal, capitalizing on the high resolution of the spectroradiometer devices. An experiment was conducted on two potted bean plants. One was maintained in good health for use as a reference while the other was treated with a photosystem II inhibitor. Collected spectra show that the fluorescence emission produces a pair of characteristic peaks superimposed on the typical leaf-specific reflectance curve. The magnitude of the fluorescence signal of the herbicide-treated leaf was four times greater than that of the control plant, thus indicating damage to the photosynthetic apparatus of the plant.