A plant-based biodegradable superabsorbent polymer enhances rice drought resilience with sustained rhizosphere microbial stability
Drought stress alters rhizosphere processes and limits rice productivity. We evaluated the effects of a biodegradable superabsorbent polymer (SAP) synthesized from banana fibers and okara on rice performance, soil properties, and rhizosphere microbial communities under growth chamber and field conditions. SAP application significantly improved plant recovery after drought stress, resulting in greater shoot biomass and seed yield than in untreated controls. In contrast, SAP had no significant effect on plant growth or yield under continuously well-watered conditions, indicating that its benefits were associated with drought mitigation. Soil analyses showed increased retention of exchangeable mineral nutrients, particularly potassium, and enhanced cation exchange capacity under controlled conditions, suggesting improved water and nutrient availability. To assess microbial responses, bacterial 16S ribosomal RNA gene and fungal ITS1 amplicon sequencing were performed. SAP amendment caused only minor changes in alpha and beta diversity, and overall bacterial and fungal community structures remained stable across cultivation environments. However, specific taxonomic shifts were observed, including a decrease in drought-associated Gemmatimonadota and an increase in Actinobacteriota. Functional prediction analysis revealed enrichment of pathways related to glycogen biosynthesis and saccharide and amino acid degradation, consistent with microbial utilization of the biodegradable SAP components. These findings suggest that SAP enhances rice drought resilience primarily by improving rhizosphere water and nutrient retention while maintaining microbial community stability. The limited but consistent taxonomic and functional shifts indicate a rhizosphere environment less constrained by water limitation and potentially more favorable for beneficial microbial activities.