Sustainable conversion of Penaeopsis serrata waste into phosphorylated chitosan for agricultural drought mitigation

Abstract

The disposal of marine waste and the intensifying effects of drought on tomato productivity are major environmental and agricultural challenges. This study valorizes shrimp shell waste by synthesizing a non-water-soluble phosphorylated chitosan (PCh) with a high degree of phosphoric substitution and evaluates its potential to enhance tomato growth under drought in a controlled greenhouse experiment. The work also addresses the limited understanding of how physicochemical properties of marine waste-derived polymers influence plant responses to drought stress. The extraction method yielded pure chitin representing about one-third of the shrimp shells. The resulting chitosan (Ch) showed strong fat- and water-binding capacities, a low degree of acetylation, and low molecular weight, suggesting its potential to improve soil moisture retention. Among the synthesized PChs, PCh1 exhibited the lowest crystallinity and highest degree of phosphorylation, reflecting enhanced structural modification and functionality. Application of PCh1 to drought-stressed tomato plants significantly increased shoot length (by up to 155%), root length (by 17%), photosynthetic pigment content (by 79–153%), and relative water content (by 12%) compared to drought-stressed controls, while reducing electrolyte leakage and oxidative stress. These findings indicate that PCh1, with a high degree of phosphoric substitution and more amorphous regions, has a stronger ability to interact with water and soil particles and enhance nutrient availability, thereby improving plant resilience and productivity under drought. This study supports circular economy strategies and highlights the potential of PCh1 as a sustainable soil conditioner. Future research should evaluate its long-term field performance under diverse crops, soils, and irrigation conditions.