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 physicochemical properties by improving aggregation, increasing cation exchange capacity, and enhancing water and nutrient retention. These changes facilitate greater uptake of essential macro- and micronutrients, supporting improved photosynthesis, root development, and biomass accumulation. At the physiological and molecular levels, HA modulates hormone signaling, activates antioxidant defenses, and primes stress-responsive pathways that enhance tolerance to drought, salinity, and other abiotic stresses. HA’s ability to regulate reactive oxygen species (ROS) homeostasis, maintain ion balance, promote osmolyte accumulation, and activate pathways such as Salt-Overly-Sensitive (SOS) or other stress-regulatory networks has been demonstrated across diverse crop species. Despite these benefits, variability arising from differences in HA source materials and extraction methods remains a major challenge for consistent application. Future research integrating multi-omics approaches, improved formulation strategies, and large-scale field validation will be essential for elucidating unknown HA’s regulatory mechanisms and maximizing its agricultural potential. Collectively, current evidence positions HA as a promising biostimulant capable of enhancing crop productivity and resilience within sustainable agricultural systems.

Humic acids (HA), with their irregular polymeric structures and largely existing in grassland, present challenges in quality control due to significant variations in biological activities depending on extraction sources. To address this, we explored industrial byproducts as potential alternatives mimicking HA-like bioactivities. This study evaluates sulfite lignin, a byproduct of the pulp industry, as an eco-friendly biostimulant for enhancing plant growth and stress tolerance. Sulfite lignin demonstrated HA-like bioactivities, promoting seed germination and salt stress tolerance in Arabidopsis thaliana. Germination assays revealed that sulfite lignin significantly improved radicle and cotyledon emergence, particularly at low concentrations (8.6 mg L⁻¹), outperforming HA and kraft lignin. Additionally, under salt stress conditions, sulfite lignin-treated plants exhibited healthier phenotypes and maintained higher chlorophyll content compared to control treatments, similar to HA and kraft lignin. The findings highlight sulfite lignin as a promising, sustainable, and cost-effective biofertilizer, effectively replicating HA's biological functions while leveraging industrial byproducts.

This study investigates the role of the NAC transcription factor ANAC032 in regulating abscisic acid (ABA)-dependent stress responses and its involvement in sugar signaling pathways. Arabidopsis seedlings with overexpressed or knock-out ANAC032 were examined for their sensitivity to ABA, glucose, and fluridone to elucidate the functional role of ANAC032 in ABA and high glucose-mediated growth retardation. Our results showed that ANAC032 negatively regulates ABA responses, as ANAC-overexpressing plants exhibited higher ABA sensitivity, while anac032 mutants were less sensitive. Under high glucose conditions, anac032 mutants demonstrated hyposensitivity, with germination rates higher than wild-type and ANAC032-overexpressing plants. Additionally, yeast two-hybrid screening identified three NAC proteins, ANAC020, ANAC064, and ANAC074, interact with ANAC032. These findings highlight ANAC032’s role in stress signaling pathways and its potential interactions with other NAC proteins, contributing to a better understanding of transcriptional regulation in plant stress responses and possibly expanding to forage crop development.