Metabolomics and physiological regulation processes unveil differential mechanisms underlying salt and alkali tolerance in roots of canola (Brassica napus L.) seedlings

Canola ( Brassica napus L.) is an important industrial crop, but soil salinization severely limits its yield and cultivation area. This study aims to elucidate the physiological response mechanisms of canola to salt and alkali stress by examining the physiological characteristics of canola seedlings and changes in organic acid metabolism in roots and secretions under salt and alkali stress using the S14 variety of canola. At low and high concentrations of salt stress, 14 and 6 differentially expressed organic acid metabolites were identified, respectively. Similarly, under low and high alkali stress concentrations, 33 and 23 organic acid metabolites were differentially expressed, respectively. Analysis of key enzyme activity in the tricarboxylic acid (TCA) cycle, organic acid content, and KEGG enrichment revealed that canola seedlings respond to salt stress primarily by increasing fatty acid metabolism, promoting energy production, and scavenging reactive oxygen species (ROS). However, the response pathway to alkali stress is distinct, suggesting that it may trigger the transformation and accumulation of glutamic acid metabolites, organic acids, and amino acids. This pathways improves energy metabolism, increasing the antioxidant capacity of crops and plays a critical role in regulating intracellular pH. Additionally, in response to salt stress, canola roots predominantly increase the secretion of substances such as 2-hydroxyisovaleric acid, 3-hydroxyisovaleric acid, kynurenic acid, and glutaric acid. Under alkali stress, canola adapts to the alkali environment by secreting increased levels of adipic acid and taurine. These findings provide a robust scientific foundation for screening and cultivation of salt-tolerant canola varieties. • Under saline-alkali stress, organic acid metabolism and root exudates of canola roots were explored. • The core response to salt stress is enhanced energy supply and reactive oxygen species scavenging. • Alkaline stress leads to the coordination of multiple pathways, such as energy metabolism, antioxidant, and osmotic regulation. • The secretion of specific organic acids by roots is a key physiological trait of canola to adapt to alkaline stress.