Abstract: To explore the tolerant extent of ryegrass seedlings to alkaline stress, ryegrass seedlings were exposed to Hoagland’s nutrient solution with NaHCO₃ added (0, 50, 100, 150, 200 mmol·L^-1), and the effects of NaHCO₃ stress on the growth of roots, metabolism of reactive oxygen species (ROS) and osmotica accumulation in roots were studied by a sandy culture in greenhouse. The results showed: Alkaline stress had significantly inhibitory effects on the roots growth of ryegrass seedlings, the inhibition was aggravated with the increasing of NaHCO₃ concentration, the maximum concentration for ryegrass in resistance to alkaline stress was 150 mmol·L^-1. With increasing NaHCO₃ stress, the contents of O^-·₂, H₂O₂ and MDA in the seedling roots increased dramatically, superoxide dismutase (SOD) activity reduced and glutathione (GSH) contents decreased significantly, the activities of catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) as well as ascorbic acid (AsA) content first increased and then decreased. The root Na⁺ content increased significantly with increasing NaHCO₃ concentration, while root K⁺ content and K⁺/Na⁺ ratio were in adverse, soluble sugar content first increased and then decreased, proline content first decreased and then increased, free amino acid content first increased, then decreased and increased again. All the above results indicated that alkaline stress caused the imbalance of ROS metabolism and the disturbance of Na⁺ and K⁺ homeostasis in the roots of ryegrass seedlings, and consumed more energy for osmotic adjustment by accumulating organic solutes, which might partly lead to its growth inhibition under alkaline stress.

Key words: alkaline stress, ryegrass, metabolism of reactive oxygen species, osmotica