Layered Double Hydroxide-Seaweed Composites Promote Seed Germination and Seedling Growth: A New Generation of Biostimulants

Adrian Alejandro Espinosa-AntónCarla Vanessa Sánchez-Hernández^*Rosalba Mireya Hernández -Herrera^*Gregorio Guadalupe Carbajal-ArizagaFabian Alejandro Rodríguez-Zaragoza

• Universidad de Guadalajara, Guadalajara, Mexico

Agricultural producers worldwide face increasing pressure to ensure food security while contending with the adverse effects of climate change and unsustainable farming practices. Layered double hydroxide (LDH) have been applied in agriculture due to their versatile properties as slow-release and efficient carriers, while seaweed extracts are widely used as plant biostimulants. However, their integrated use as nanostructured composites for enhancing seed germination and seedling growth remains unexplored. In this study, we addressed this gap by synthesizing composites that combine cationic LDH nanosheets with anionic compounds present in alkaline extracts of the brown seaweed Sargassum liebmannii (LDH-Sargassum) and the green seaweed Ulva ohnoi (LDH-Ulva). Physicochemical characterization confirmed that approximately 12% of the composite mass corresponded to seaweed-derived molecules adsorbed onto the LDH surface. The biological efficacy of the composites was assessed through seed germination and early seedling development assays in tomato (Solanum lycopersicum L. cv. Rio Grande) and root induction assays in mung bean (Vigna radiata L.) cuttings. Both LDH-Sargassum and LDH-Ulva significantly improved germination and seedling growth at lower concentrations (1.57, 3.14, and 6.28 mgmL⁻¹), while higher doses (12.56– 50.25 mgmL⁻¹) produced effects that were either comparable to those of the control or slightly better. Notably, both composites enhanced root architecture in mung bean cuttings by increasing root number, length, and dry weight. These results highlight the potential of LDH-seaweed composites as effective biostimulants, particularly in promoting early-stage root development by improving root branching, size, and biomass. Notably, LDH-Sargassum at a concentration of 6.28 mg·mL⁻¹ emerged as a promising natural alternative to synthetic root-promoting agents. This work demonstrates for the first time the feasibility of LDH-seaweed composites as next-generation nanostructured phycobiostimulants, providing insights into their interactions with plants and identifying optimal application dosages. These findings provide a foundation for implementing LDH-seaweed composites as a sustainable strategy to reduce agrochemical and provide a novel and practical pathway to strengthen food security through bio-based nanotechnologies.