Mechanistic Insights into Humic Acid-Mediated Enhancement of Crop Productivity and Stress Tolerance

Abstract

Humic acid (HA), a key component of soil organic matter, has emerged as a multifunctional biostimulant that enhances soil quality,nutrient availability, plant growth, and stress resilience. The complex supramolecular structure of HA influences soil physicochemicalproperties by improving aggregation, increasing cation exchange capacity, and enhancing water and nutrient retention. These changesfacilitate greater uptake of essential macro- and micronutrients, supporting improved photosynthesis, root development, and biomassaccumulation. At the physiological and molecular levels, HA modulates hormone signaling, activates antioxidant defenses, and primesstress-responsive pathways that enhance tolerance to drought, salinity, and other abiotic stresses. HA’s ability to regulate reactiveoxygen species (ROS) homeostasis, maintain ion balance, promote osmolyte accumulation, and activate pathways such asSalt-Overly-Sensitive (SOS) or other stress-regulatory networks has been demonstrated across diverse crop species. Despite thesebenefits, variability arising from differences in HA source materials and extraction methods remains a major challenge for consistentapplication. Future research integrating multi-omics approaches, improved formulation strategies, and large-scale field validation will beessential for elucidating unknown HA’s regulatory mechanisms and maximizing its agricultural potential. Collectively, current evidencepositions HA as a promising biostimulant capable of enhancing crop productivity and resilience within sustainable agricultural systems.