Sensitivity to Foliar Anthocyanin Content of Vegetation Indices Using Green Reflectance

Anthocyanins are nonphotosynthetic water-soluble pigments associated with the resistance of plants to environmental stresses such as drought, low soil nutrients, high radiation, herbivores, and pathogens. Information on the absolute and relative amounts of anthocyanins allows evaluating the physiological conditions of plants and their responses to stress and has the potential for evaluating plant species diversity across broad geographic regions. As anthocyanins absorb radiation in the green region of the electromagnetic spectrum (with a peak of absorption at around 540-560 nm), broadband vegetation indices that use this spectral region in their formulation will exhibit sensitivity to their presence. In this letter, we evaluate the sensitivity of four broadband vegetation indices using reflectance in the green spectral region to foliar anthocyanin content. Among the indices tested, the visible atmospherically resistant vegetation index was found to be closely and linearly related to the relative amount of foliar anthocyanin across five different species (the root-mean-square error of the prediction is ca. 0.1, and the relative error is below 20%). While this result was obtained at leaf level, it opens new possibilities for analyzing anthocyanin content and composition across multiple scales by means of spacecraft-mounted broadband sensor systems such as Landsat Thematic Mapper, Landsat Enhanced Thematic Mapper Plus, and Moderate Resolution Imaging Spectroradiometer.