Innovative multiscale phenotyping approach on Amaranthus spp. leaves reveals contrasting differentiation traits at young stage

Imaging analysis can aid in phenotyping plant morphological traits at different scale levels, with options ranging from microscopy images to remote sensing acquisitions. Through this approach, it is possible to gain a minimally invasive understanding of physiological and structural trait diversity, as well as the relationship between plants and the environment. Much attention has already been paid towards the high phenotypic plasticity of the Amaranthus genus, as it includes highly invasive weed species harmful to summer crops. The identification of morpho-anatomical traits in amaranth leaves at early stage could be beneficial in gaining a greater understanding of the relation between their structural characters and their performance in the agroecosystem. In this work, we applied an innovative multi-scale phenotyping approach on single leaf morphometric traits of four Amaranthus species (A. hybridus, A. palmeri, A. retroflexus and A. tuberculatus) by processing digital images of intact leaves and confocal reflection microscopy acquisitions on adaxial surface imprints. The analysed morphometric variables belonged to three groups: macroscopic leaf traits, evapotranspiration-related traits and microscopic traits related to the leaf surface. The results evidenced that different investigation levels contribute to revealing species-specific characters even at a juvenile stage, which is crucial for plant development and the establishment of competition. In detail, some variables concerning macroscopic and evapotranspiration-related traits were those that best discriminated A. tuberculatus from the other three species. The approach proved to be an effective, reliable, and low-impact procedure for describing the functional characteristics of phylogenetically related species and quantifying traits associated with taxonomy and biodiversity studies.