Molecular Basis and Mechanistic Insights into Ascophyllum nodosum Extract-Mediated Regulation of Plant Growth, Nutrient Acquisition, and Stress Responses

Ascophyllum nodosum extracts (ANE) are widely used biostimulants associated with improvements in plant growth, productivity, nutrient acquisition, and abiotic stress tolerance. However, the molecular mechanisms linking extract composition to plant signaling and physiological responses remain incompletely resolved. ANE contains a complex mixture of bioactive constituents, including polysaccharides, osmolytes, phenolic compounds, and phytohormone-like molecules. Their composition varies according to biomass source, environmental conditions, and extraction methodology, contributing to variability in biological activity. Current evidence suggests that ANE functions mainly as a signaling modulator rather than a direct nutrient source. ANE treatment has been associated with early cellular responses, including cytosolic Ca2+ influx, reactive oxygen species (ROS) generation, and mitogen-activated protein kinase (MAPK)-associated signaling events. However, many proposed mechanisms remain unresolved, and a considerable proportion of the available mechanistic evidence originates from studies using purified ANE-derived polysaccharides or related elicitor systems. ANE-associated responses include modulation of nutrient transport, primary metabolism, hormonal regulation, transcriptional reprogramming, and stress-responsive pathways, contributing to improved root development, nutrient acquisition, and defense-related responses. Nevertheless, limited knowledge of receptor-mediated perception mechanisms, signaling hierarchies, and extract-dependent variability continues to constrain mechanistic understanding and reproducibility. Future research should prioritize receptor identification, bioassay-guided fractionation, integrated multi-omics approaches, and improved standardization of extraction and formulation procedures. These advances will be essential for establishing robust mechanistic models and supporting the development of evidence-based ANE biostimulants for sustainable crop production.