Spectral and time-resolved fluorescence signature of four weed species as affected by selected herbicides

In the present study we show for the first time the suitability of the laser-induced fluorescence technique to evaluate in vivo herbicide-induced damages as revealed by changes of fluorescence spectra and lifetime. Four herbicides of different modes of action (glyphosate, bromoxynil, mesotrione, and amitrole) were selected and applied to four weed species (Stellaria media, Setaria viridis, Chenopodium album, and Viola arvensis). Modifications of the fluorescence signature depended on the agrochemical – plant species interaction as well as on the time after application. Measurements in the red and far-red spectral region reveal disturbances in the functionality of the photosynthetic apparatus and chlorophyll concentration, e.g. after application of bromoxynil or mesotrione. Recordings in the blue and green spectral regions indicate changes of both amount and composition of specific fluorophores, i.e. after application of glyphosate and amitrole. In all spectral measurements, the position of peak maxima was not affected by herbicide application. The fluorescence lifetime, expressed as LTmean or as lifetime 1 (LT1, short-duration) and LT2 (long-duration) fractions, provided additional information to the spectrally resolved data. Thereby, significant alterations of the lifetime duration and fractional characteristics were observed at specific wavelengths, e.g. after application of bromoxynil, mesotrione, or amitrole.

On the left: characteristic fluorescence decay curve (smoothed) measured at 450, 550, 680, and 740 nm on control plants of Chenopodium album. On the right: impact of selected herbicides on both the duration and contribution of Lifetime 1 (LT 1) and Lifetime 2 (LT 2) measured at 450 nm on C. album four (first stacked bar) and eleven (second stacked bar) days after treatment (right).Figure optionsDownload as PowerPoint slideHighlights
► The herbicide-induced modification of the fluorescence (400–770 nm) was evaluated.
► Temporal changes in the spectra and lifetime were herbicide and species-specific.
► B and G fluorescence suggest alterations in amount and composition of fluorophores.
► Chlorophyll fluorescence was strongly affected by bromoxynil and mesotrione.
► Fluorescence lifetime supports a better understanding of the impact of herbicides.