Carbon quantum dots in plant photosynthesis: from material design to agricultural performance

Sustainable agricultural intensification requires nanomaterials that regulate plant physiology while improving resource-use efficiency and stress resilience. Carbon quantum dots (CQDs) have emerged as photosynthetic nano-regulators because their optical and electronic properties, surface functionality, dispersibility, and compositional flexibility enable control over plant uptake and activity. This review develops a structure-function-performance framework linking CQD physicochemical characteristics, including particle size, surface chemistry, optical properties, and heteroatom doping, with transport and photosynthetic regulation. Five interconnected mechanisms are identified: enhanced electron transport, improved light harvesting and spectral conversion, redox homeostasis and antioxidant regulation, chlorophyll biosynthesis and protection, and enhanced carbon fixation. Their evidentiary strength varies, with chloroplast-level evidence providing the strongest support for CQD-mediated electron-transport enhancement, whereas the other mechanisms are supported primarily by physiological, biochemical, photochemical, molecular, and transcriptomic observations. Multi-omics studies further indicate that CQD responses extend beyond photosynthesis into nutrient acquisition, carbon and nitrogen metabolism, and stress adaptation. Reported applications include seed priming, photosynthetic enhancement, abiotic-stress mitigation, nutrient-use efficiency, and spectral-conversion strategies. However, limited long-term field validation, and uncertainties surrounding scalability, economic viability, environmental fate, and soil-climate dependence remain major barriers to agricultural translation. This review identifies mechanistic gaps and priorities for developing reproducible, environmentally responsible CQD technologies.