Algal-Based Biostimulants and Biofertilizers: Bridging Bioremediation and Sustainable Agriculture

Algae-based biostimulants and biofertilizers support crop performance and environmental remediation. Seaweeds and microalgae supply small amounts of growth-promoting compounds, including phytohormones, amino acids, osmoprotectants, and anionic polysaccharides. These compounds stimulate root development and improve nutrient use efficiency. They also help plants tolerate abiotic stress, which includes drought, salinity, and heat. Nitrogen-fixing cyanobacteria contribute biologically available nitrogen and release molecules that facilitate micronutrient delivery to the rhizosphere. Algal biomass contributes to bioremediation. It binds heavy metals, captures phosphate and promotes microbial degradation of pesticide residues. These effects can reduce leaching and runoff. Field applications often deliver higher yields or allow fertilizer savings while lowering nitrate loss and metal uptake. Harmonized regulations in the European Union are streamlining market entry for algae-based biostimulants. Key challenges remain. Seasonal changes in biomass composition affect product consistency. Liquid extracts show limited shelf life in warm supply chains. Decision-support tools for optimizing dose and timing are not yet widely available. Advances in controlled cultivation and strain selection can stabilize biomass quality. Improved formulation technologies, including microencapsulation for stability and controlled release, can extend shelf life and facilitate field application. Integrated algal biorefineries can increase profitability and align production with circular and climate-smart agriculture. The aim of this chapter is to present the potential of algae as biostimulants and fertilizers, as well as agents supporting bioremediation. The chapter discusses the biochemical profile of algae in the context of their importance in plant–soil systems and the mechanisms of action of algae-based biofertilizers and biostimulants, as well as the use of algae in bioremediation, presenting examples of successful research and commercialization. The chapter addresses legal issues in marketing algae-based products, with particular emphasis on the European Union compared to the USA and Asia.