Carbon quantum dots priming alleviate drought stress in Elymus sibiricus by enhancing photosynthesis and carbohydrate metabolism

Drought stress severely restricts the growth and productivity of Elymus sibiricus (E. sibiricus). Seed priming with carbon quantum dots (CQDs) emerges as a promising strategy to enhance plant stress tolerance, yet its core regulatory mechanism in E. sibiricus remains unclear. In this study, we performed an integrated analysis of physiology, transcriptome, and metabolome to elucidate the mechanism by which CQDs alleviate drought stress. Seeds primed with an optimal concentration of 50 mg/L CQDs exhibited significant improvements in plant height, biomass, and photosynthetic efficiency under drought conditions. Mechanistically, CQDs enhanced drought resistance through a three-tiered synergistic pathway: photosynthetic protection, by maintaining chlorophyll homeostasis and upregulating key genes associated with photosystems I/II to alleviate photoinhibition; oxidative stress alleviation, via activating antioxidant enzymes and accumulating osmoprotectants to scavenge reactive oxygen species and sustain cellular homeostasis; and carbon metabolism reprogramming, by promoting starch degradation and the glyoxylate cycle to optimize carbon allocation and energy supply. Key hub genes (EsGLCAT14A, EsHT1, and EsCBSX5) involved in cell wall remodeling and energy metabolism were identified as critical regulators. Collectively, this study elucidates that CQDs confer drought tolerance in E. sibiricus through the coordinated integration of photosynthetic protection, redox balance, and metabolic reprogramming, providing a theoretical foundation and technical support for applying nanomaterials in stress-resistant cultivation of forage crop.