Boosting Photosynthesis in Choy Sum ( Brassica napus L.) via Foliar Spray of Blue and Red Emissive Carbon Dots

As the foundation of plant growth, photosynthesis efficiency has a direct influence on crop productivity. This study fabricated blue- and red-emissive carbon dots (BR-CDs) that convert natural light into red and blue light, which chloroplasts absorb more readily, enhancing solar light use and promoting choy sum ( Brassica napus L.) growth. Experimental results indicate that BR-CD-treated choy sum showed a 17.0% increase in shoot fresh weight (FW) and a 145.4% increase in root FW compared to the control group. The dry weight (DW) also increased by 95.8% and 150.0% in the respective samples. Furthermore, the leaf area expanded by 25.0%, and the carbohydrate content improved by 115.2%. Theoretical calculations also indicated that BR-CDs are abundant in electron-donating groups, which promote electron transfer during photosynthesis. Femtosecond transient absorption (fs-TA) spectra showed that BR-CDs boost chloroplast light absorption and improve energy transfer efficiency, mainly by first increasing blue light absorption and then transferring that energy to red light. The mechanism significantly improves photosynthetic efficiency in choy sum treated with BR-CDs. It is noteworthy that the expression levels of blue-light-related genes (phototropins and cryptochromes) and red-light-related genes (phytochromes A and B) in choy sum were significantly increased after treatment with BR-CDs. This study highlights the potential of BR-CDs for improving solar light utilization and provides strategies for enhancing agricultural productivity and sustainability.