Harnessing Algal Biomass: Superabsorbent and Biostimulant Hydrogels for Seed Germination in Soilless Cultivation

Hydrogels are emerging as sustainable alternatives to petroleum-based foams and pots in horticulture due to their high porosity, enhancing water and nutrient retention. This study develops κ-carrageenan (Carr)-based hydrogels incorporating hydrolyzed (HSW) and nonhydrolyzed red seaweed (WSW) (0–50 wt %) to introduce biostimulant properties for soilless cultivation. Hydrogels were analyzed for swelling in different media, solubility, microstructure (SEM), physicochemical interactions (FTIR, XRD), and mechanical properties, revealing high porosity, superabsorbent behavior (swelling up to 6000%), and reduced compression modulus with increasing seaweed content. Their biostimulant effect was assessed on Arabidopsis thaliana, with 20 wt % HSW hydrogels promoting enhanced root and shoot growth. Additionally, the hydrogels inhibited Fusarium solani, demonstrating antifungal properties. These results highlight the potential of Carr-seaweed hydrogels as multifunctional substrates for sustainable plant cultivation.