Molecular mechanism of saline-alkali stress tolerance in the green manure crop Sophora alopecuroides

Selecting suitable plants as green manures is essential for improving marginal soil fertility and sustainable agroecosystems. Sophora alopecuroides is a highly salt- and alkali-tolerant leguminous plant that is often used as green manure. However, the molecular mechanism underlying saline-alkali tolerance in S. alopecuroides remains largely unclear. In this study, we investigated the molecular mechanisms underlying saline-alkali stress tolerance through physiological and transcriptomic analyses in S. alopecuroides seedlings. Comparative transcriptome analysis revealed that saline-alkali stress induced the expression of genes involved in cell wall modification, thereby increasing the contents of pectin and hemicellulose in roots and improving saline-alkali stress tolerance. The expression of genes related to the glycolysis pathway was induced, whereas genes involved in the TCA cycle and primary nitrogen metabolism were downregulated under salt and alkali stresses, indicating that S. alopecuroides plants modulate carbon flow to provide energy and ultimately regulate saline-alkali stress adaptation. Saline-alkali stress also modulated phytohormone signaling pathways in S. alopecuroides. Moreover, the leaves of seedlings under salt and alkali stresses contained elevated potassium, zinc and manganese contents, and the roots of seedlings under salt stress contained higher iron content. Taken together, these adaptive mechanisms to saline-alkali stress provide a physiological basis for the coordinated nutrient cycling of S. alopecuroides green manure. These results provide a molecular basis for the phytoremediation and utilization of saline-alkali soil, enabling the design of an integrated nutrient cycling system and optimization of the cultivation and field management of S. alopecuroides green manure.