Pleurotus eryngii Stipe Base-Derived Carbon Dots Enhanced the Growth and Salt Tolerance of Tomato

Soil salinity severely limits tomato growth by impairing photosynthesis and redox balance. Carbon dots (CDs) have emerged as promising nanomaterials to promote growth and enhance stress tolerance. In this study, we synthesized and characterized CDs derived from <i>Pleurotus eryngii</i> stipe bases (PbCDs), with rich hydrophilic groups including carboxyl groups and secondary amines. The particles were uniform, with an average diameter of 4.17 nm, and exhibited blue fluorescence. Importantly, PbCDs significantly promoted tomato growth under control and salt conditions. Under salt conditions, PbCD-treated plants showed enhanced shoot and root growth, larger leaf area, and growth comparable to control plants without stress. Interestingly, PbCD treatment of the plants enhanced cell expansion under control conditions and promoted cell division under salt conditions. In addition, PbCD-treated plants had higher chlorophyll content, net photosynthetic rate, and maximum quantum efficiency of PSII, which alleviated the inhibition caused by salinity. Furthermore, PbCDs also reduced oxidative damage by lowering O₂^•-, and H₂O₂ levels, while activating antioxidant enzymes (superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase) under salt stress. Overall, PbCDs promoted tomato growth and conferred salt tolerance through coordinated regulation of the cell cycle, photosynthesis, and antioxidant defenses, supporting their potential as sustainable nanomaterials for crop improvement in saline soils.