Regulation Mechanisms of Nitrogen-Doped Carbon Dots in Enhanced Maize Photosynthesis under Drought Stress

Herein, greenhouse experiments were designed to reveal the role of nitrogen-doped carbon dots (N-CDs) in enhancing maize drought tolerance. Two humidity conditions were created: adequate watering (soil moisture, 75%) and drought stress (soil moisture, 35%). Corn seedlings were harvested after spraying the N-CD solution (5 mg center dot L-1) on maize leaves for 5 days. The results indicated that foliar application of N-CDs increased the net photosynthesis rate (28.6%) of maize, and the fresh and dry weights of roots and shoots increased by 224.5, 360.0, 230.8, and 63.3% under drought stress, respectively. N-CDs showed high reactive oxygen species (ROS)-scavenging activity, resulting in enhanced superoxide dismutase activity (26.7%) and reduced malondialdehyde enzyme activity (18.9%). Besides, N-CDs could be used as light-harvesting materials to improve the light utilization efficiency, upregulate psbA gene expression (81.7-fold), and promote fast synthesis of the D1 protein, which could repair photosystem II under drought stress. Therefore, foliar-sprayed N-CDs could improve photosynthesis through multiple pathways under drought stress: light harvesting, photoprotection, and light repairing. Then, N-CD exposure reduced the corn yield loss under drought by nearly 30% compared with those of the control groups in a full life cycle study. Therefore, this study found for the first time that N-CD-enabled nanoagriculture could ensure crop growth and yield under drought stress, which would be important for global crop cultivation and a promising alternative to deal with the global climate change.