Biomass-Derived Carbon Dots for Agriculture: Reactive Oxygen Species-Mediated Stress Tolerance, Postharvest Preservation, and Designing for Safety

Rising climate volatility and persistent postharvest losses demand agricultural technologies stabilizing yield and preserving quality while minimizing unintended ecological impacts. Biomass-derived carbon dots (BCDs) have emerged as a versatile class of zero-dimensional carbon nanomaterials, whose optical, redox, and interfacial properties can be tuned through precursor selection, heteroatom doping, and surface functionalization. This Review maps key structure–property–function relationships that underpin BCD-enabled abiotic and biotic stress tolerance, including ROS scavenging, modulation of antioxidant and defense pathways, improved nutrient utilization, and enhanced photosynthetic performance. We further summarize how BCD-based composite coatings and packaging systems delay senescence and microbial spoilage via antimicrobial, antioxidant, UV-shielding, and barrier effects, with growing interest in fluorescence-enabled freshness monitoring. Beyond performance, we emphasize a safe-by-design approach that links physicochemical descriptors to fate, transport, and exposure across plant, soil, and food-chain compartments. Finally, we outline actionable priorities, standardized characterization, dose–response benchmarking, mechanism-resolved studies, and scalable green synthesis, to accelerate responsible translation.