Root physiological, biochemical and untargeted metabolomic responses of five forage pea (Pisum sativum L.) varieties at seedling stage to saline-alkali stress in Qaidam salinized soil.

Soil salinization in the Qaidam Basin represents a significant abiotic stressor that restricts the growth, development, and yield of forage pea (Pisum sativum L.). This study evaluated five forage pea genotypes grown under naturally salinized field conditions in the Qaidam Basin (mean electrical conductivity (EC) 4.5-7.0 dS·m⁻¹, total salt 2.37 g·kg⁻¹). Given the absence of a non-saline control, our analyses primarily focused on genotypic differences in morphological, physiological, and metabolic traits under salinized soil rather than establishing causal stress-response relationships. By integrating morphological phenotyping, physiological and biochemical assays, and untargeted metabolomics, we systematically compared performance and root metabolic profiles among the five genotypes. Significant differences in saline-alkali tolerance-related traits were observed among the five genotypes (P < 0.05). Based on comprehensive assessment of multiple growth traits (plant height, root length, lateral root number, and field emergence rate), Qingjian No. 1 and Dingwan No. 8 were identified as genotypes exhibiting superior performance under salinized conditions, with GH8 demonstrating the best performance in plant height (12.50 ± 0.90 cm) and root length (11.80 ± 1.30 cm). Conversely, Grassland No. 7 and Grassland No. 23 were classified as less adapted genotypes, with GH23 exhibiting the shortest plant height (5.40 ± 0.50 cm) and root length (4.00 ± 0.80 cm), indicating severe growth suppression. At the physiological level, GH8 and GH12 exhibited the highest 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging activity; GH8 accumulated the highest levels of soluble protein, soluble sugar, and proline (proline: 250.0 µg·g⁻¹); whereas GH1 and GH8 showed the lowest malondialdehyde accumulation. Untargeted metabolomic analysis identified 5,193 non-redundant metabolites, with amino acids and their derivatives constituting 31.25% of the core category. A total of 75 common differential metabolites were identified across genotypes. Root length, lateral root number, catalase activity, soluble sugar content, and secondary metabolite accumulation emerged as key indicators for evaluating genotypic performance under salinized conditions. This study provides a multi-trait comparative analysis of forage pea genotypes grown in naturally salinized soil of the Qaidam Basin and reveals the physiological and metabolic patterns underlying genotypic differences, offering a theoretical basis for salt-tolerant variety breeding in high-altitude salinized regions.