Dose-Dependent Effects and Metabolomic Analysis of Foliar-Applied Carbon Dots on Cotton (Gossypium hirsutum L.) Growth
While carbon dots (CDs) are promising green nanomaterials for sustainable agriculture, how they regulate cotton growth via physiological and metabolic reprogramming remains poorly understood. This study evaluated foliar CD application (0–200 mg·L−1) to uncover dose–response patterns and metabolic drivers. CDs exerted a concentration-dependent impact, with 100 mg·L−1 yielding optimal results. This application markedly boosted shoot and root biomass (fresh weight: 103.43% and 44.28%; dry weight: 56.03% and 40.39%) and enhanced specific leaf area by 52.51% over the control. CDs improved photosynthetic efficiency (elevated Pn, Gs, and E values, alongside increased chlorophyll a and carotenoids) and strengthened antioxidant defenses (enhanced leaf POD/SOD and root POD/CAT activities). Despite mild MDA increases indicating oxidative stress, accumulated proline and soluble sugars in roots suggested adaptive osmotic adjustment. These findings suggest that CDs maintain physiological homeostasis by modulating antioxidant defense and osmotic adjustment. Untargeted metabolomics identified 2440 metabolites. Phenylpropanoid biosynthesis and flavonoid biosynthesis were the most prominently enriched pathways based on KEGG enrichment results. K-means and correlation analyses revealed key metabolites linked to cotton biomass. Overall, CDs facilitate cotton development through synergistic physiological and metabolic reprogramming, underscoring their potential as innovative agricultural growth regulators.