Carbon quantum dots from fallen leaves of Lonicera caerulea L.: An innovative plant growth promoter and fruit quality enhancer.

With increasing environmental pollution and resource wastage, utilizing waste for high-value applications has become crucial. This study explores the preparation of carbon dots (CDs) from blue honeysuckle leaves and their potential in enhancing plant photosynthesis. CDs derived from these leaves have a particle size of ∼2.6 nm and emit blue fluorescence under 365 nm UV light, making them suitable for foliar spraying. When applied, CDs enter leaf cells and impact chloroplasts, significantly improving photosystem II (PSII) performance and Rubisco enzyme activity. At an optimal concentration of 1000 mg/L, PSII electron transfer efficiency and Rubisco activity increased by 29.84% and 208.12%, respectively, boosting net photosynthetic rate by 60.4%. This treatment also enhanced blue honeysuckle yield and fruit quality, with higher levels of soluble solids, ascorbic acid, flavonoids, anthocyanins, and total phenolics. These improvements were linked to increased sucrose synthesis (up 25.99%) and leaf assimilative capacity (up 25%). Additionally, CDs enhanced post-harvest soil enzyme activity and microbial abundance, promoting nutrient cycling and soil utilization. This study demonstrates that preparing CDs from waste blue honeysuckle leaves not only mitigates environmental pollution but also offers a sustainable, high value use for plant resources. The findings highlight the potential of nanomaterials in improving agricultural productivity and provide a novel pathway for waste reuse.