Humic Acids as Drivers of Plant Growth: Regulating Root Development and Photobiology Through Redox Modulation

This study investigates the effects of humic acids (HA) derived from oxidized sub-bituminous coal on plant growth, focusing on root development and photobiology. An optimal HA concentration of 20 mg L−1 of carbon was found to significantly enhance morphological and photobiological parameters. HA modulates electron transport across the thylakoid membrane, influencing ATP synthesis, and improves root growth by enhancing finer root diameter classes, which aids nutrient absorption. It stimulates rapid ROS production, boosts antioxidant enzyme activities, and increases H+-ATPase activity in roots. HA also induces the expression of genes related to root hair growth and other growth-related pathways. The study concludes that HA promotes plant development by modulating oxidative stress through the RBOH/ROS/auxin/H+-ATPase pathways and potentially influences photobiological processes, contributing to a positive membrane oxidative balance that supports root growth and development.