Synergistic Seedling Responses of Distinct Oat Cultivars to Compound Saline–Alkali Stress: Phenotypic, Physiological, and Metabolomic Mechanisms

Abstract

Simple Summary Soil salinization and alkalinization severely restrict crop growth and agricultural production in cold highland areas. Most previous studies on oats have only focused on single-salt stress, whereas systematic and multi-dimensional investigations of oat responses to compound salt–alkali stress remain limited. In this study, three oat cultivars with distinct salt tolerance levels were selected to investigate their growth performance, physiological responses, and internal metabolic regulation under compound salt–alkali stress that simulates the soil environment of local highland regions. The results indicated that compound salt–alkali stress significantly inhibited oat growth and induced cellular damage. The highly salt-tolerant oat cultivars exhibited superior stress adaptability by enhancing the activities of protective enzymes and accumulating osmoprotective substances. Key metabolic pathways associated with stress tolerance were identified, among which flavonoid biosynthesis played a critical role in stress resistance. Specifically, tolerant oat cultivars activated both defensive response and energy metabolism pathways to cope with stress, while sensitive cultivars only displayed basic passive stress responses. These findings provide valuable insights for the screening and breeding of salt–alkali-tolerant oat cultivars, and support the sustainable development of agriculture in cold highland regions.