Laser-induced fluorescence signatures as a tool for remote monitoring of water and nitrogen stresses in plants

We tested the potential of leaf fluorescence as a tool for the remote sensing of water and nitrogen stresses in agricultural crops, as compared to the conventional contact techniques of leaf tissue or soil analysis. Multi-wavelength excitation fluorescence and diurnal behavior of the variable chlorophyll fluorescence were used to monitor nitrogen deficiency in corn (GEOIDE RES#54 network project, Canada) and water stress in pea plants (LURE project, France). Variable chlorophyll fluorescence was found to be a very sensitive tool, giving early indications of the drought stress and general indications of a misfunction of the photosynthetic apparatus. Some fluorescence parameters derived from ultraviolet (UV) and visible light (VIS) excitation of chlorophyll, especially the ratio FRFexUV/FRFexVIS measuring the epidermis UV transmittance, seemed to be more specifically related to the nitrogen content of leaves and precluded an ambiguous response as in the case of the more complex ratio BGF/ChlF. Despite the high variability of the biological material in the field, fluorescence could discriminate between N-deficient and N-saturated plants, and between water-stressed and non-water-stressed plants in the early stages of stress development.