Mechanistic insights into bio-based fertilisers, biostimulants, and novel delivery systems in plant physiology

The transition toward sustainable agriculture requires fertilisation strategies that improve nutrient use efficiency, enhance resilience to abiotic and biotic stress, and minimise environmental impacts. Bio-based fertilisers, biostimulants, and novel delivery systems have emerged as promising alternatives or complements to conventional agrochemicals, yet their physiological bases remain only partially understood. This review examines current knowledge on the mechanistic pathways through which these products act and identifies research gaps to enable predictive use in diverse cropping systems. Evidence indicates that bio-based inputs influence plant performance by modulating nutrient uptake and assimilation, hormonal and redox signalling, stress perception and defence priming, and biomass allocation. Protein hydrolysates, humic substances, and seaweed extracts alter root morphology, ion transport, and stress signalling, while microbial inoculants such as rhizobia, phosphate-solubilising bacteria, and arbuscular mycorrhizal fungi provide nutrient mobilisation and immune priming. Novel delivery systems, including clays and encapsulation systems, extend these effects by improving the stability and targeted release of bioactive compounds. Despite these advances, the lack of standardised protocols, incomplete dose-response characterisation, and strong context dependence of plant responses remain major obstacles to reproducibility and scalability. Progress in this field requires a mechanistically anchored approach that links molecular events (such as transporter activation, hormone dynamics, and antioxidant activity) to agronomic outcomes under variable environments. Embedding mechanistic descriptors into both experimental design and regulatory frameworks could accelerate the translation of bio-based inputs into reliable tools for sustainable crop production, supported by environmental impact assessments.