Moderate Light Intensity Optimizes Forage Nutritive Value While Maintaining Morphophysiological Stability and...

Plantago lanceolata L. is increasingly incorporated in temperate pasture systems for its agronomic resilience and potential to reduce the environmental footprint of ruminant production through its specific secondary metabolites (SMs). However, how light intensity per se regulates P. lanceolata L. physiology, nutritive value and SM accumulation remains poorly understood due to confounding factors in field studies. This controlled-environment study evaluated the effects of three light intensities (200, 300, and 400 µmol photons m^-2 s^-1) on morphophysiological traits, forage quality, and SM concentrations in P. lanceolata L. cv. "Ceres Tonic". Plants were grown in controlled-environment chambers under similar temperature, humidity and nutrient conditions. Morphological traits, biomass allocation, chlorophyll fluorescence, gas exchange, chemical composition, and root architecture were measured. Additionally, the most important secondary metabolites, aucubin, catalpol and acteoside, were also evaluated. Under the different light intensity treatments plants maintained stable physiological parameters, total biomass production, leaf dimensions or root architecture. However, moderate light intensity (300 µmol photons m^-2 s^-1) optimized nutritive value by minimizing fiber concentrations and maximizing metabolizable energy. Acteoside concentration, as well as the iridoid glycosides aucubin and catalpol, were not affected by the different light intensities. These findings demonstrate that P. lanceolata L. maintains morphophysiological stability across the tested light intensity range studied, while selectively modulating forage quality.