Graphene ameliorates saline-alkaline stress-induced damage and improves growth and tolerance in alfalfa (Medicago sativa L.).

Nanoscience is leading to the production of nanotech applications to enhance growth and environmental stress tolerance of plants. However, there are few studies on the morphological and physiological regulative mechanism of coupling effects between graphene (Nano-C) and pH in alfalfa, especially both in promotion and phytotoxicity effect by Nano-C under abiotic stress. The coupling effects of Nano-C and pH on plant growth, photosynthetic parameters and enzymes of the antioxidant defence system on leaves and roots were investigated at graphene concentrations of 0, 5, 10, and 20 g kg-1 in pots trials. The result showed a significantly promoted the plant growth at treatment of 5 g kg-1 Nano-C, whereas 10-20 g kg-1 Nano-C harmed the physiological and morphological characterizations. Under salt and alkali stresses, the dry weight, fresh weight, seedling length and antioxidant enzymes activities were increased significantly at 5 g kg-1 Nano-C treatment. These findings revealed that 5 g kg-1 Nano-C enhanced alfalfa tolerance by modulating various morphological and physiological characteristics. Meanwhile, through models analyses, the equivalent coupling effects of Nano-C and pH were located at rectangular area defined by 5.43-7.80 Nano-C combining 8.59-8.96 pH value, and the final optimal application of Nano-C was at 6.57 g kg-1 when high exposure dose of Nano-C indeed resulted in phytotoxicity to the plant. Results of the model analyses also showed significant synergistic effects on the photosynthesis and antioxidant system. Overall, our findings suggested fundamental insights into carbon nanomaterials-mediated physiological adaptation in plants.