Calcium Alginate-Based Hydrogel-Encapsulated Nutrients and Nucleic Acid Delivery for Ameliorating Saline–Alkali Stress in Plants

Calcium alginate is an anionic polysaccharide that forms an ionically crosslinked hydrogel network with encapsulation properties to nucleic acids and nutrients for the amelioration of osmotic stress, ion toxicity and nutrient imbalance in saline–alkali soils. Traditional soil reclamation methods, including salt leaching, incorporation of organic matter, and gypsum application, are water-intensive under a changing climate, ultimately necessitating transformative bio-based solutions for food security. Calcium alginate-based biohydrogel represents a versatile platform with a tunable macromolecular architecture, ionic crosslinking via an “egg box” mechanism and potentially promising to deliver engineered co-encapsulated nutrients and genetically modified cargoes. The mannuronic (M) and guluronic (G) acid (M/G) ratios govern ion exchange capacity, rheological behavior and release kinetics in saline- and alkali-stressed environments. Recent studies on alginate-based nutrient encapsulation showed reduced oxidative damage and a 15–50% increase in plant-available water. The irrigation intervals extended from 7 to 14 days and yield gains by 24% in wheat, with comparable improvements in maize, tomato, rice and cotton. Calcium alginate hydrogels encapsulated salt tolerance genes (HKT1, SOS1, AVP1) encoding proteins mainly involved in Na+ retrieval from xylem, Na+ extrusion from root cells and vacuolar Na+ sequestration, which have achieved yield gains of 40 to 75% across wheat, rice and maize. Future research should focus on optimizing mechanical strength, crosslinking chemistry and smart bioencapsulation strategies for sustainable development so that crops are capable of withstanding variable climate stresses.