Physiological and comparative transcriptome analysis of leaf response and physiological adaption to saline alkali stress across pH values in alfalfa (Medicago sativa).

Abstract Soil salinization is a critical factor limiting growth and causing physiological dysfunction in plants. The damage from alkaline salt in most plants is significantly greater than that from neutral salt. However, there is still a lack of research on the action mechanism by which saline alkali stress on plants under the same salt concentration across different pH values. The present study examined the effects of different pH values (7.0, 8.0, 9.0, and 10.0) under the same salt concentration (200 mmolL−1) on photosynthetic function, photoprotective mechanism, nitrogen metabolism, and osmotic regulation in alfalfa (Medicago sativa) leaves, including a transcriptomic analysis of changes in gene expression related to the above metabolic processes. The results showed that low pH saline alkali stress (pH 7.0 and 8.0) promoted chlorophyll synthesis in alfalfa leaves, and non-photochemical quenching (NPQ) and cyclic electron transfer (CEF) were promoted. There was no significant effect on plant growth or photochemical activity. The soluble sugar, proline, and soluble protein contents did not change significantly, and there was no obvious oxidative damage in alfalfa leaves. However, when pH increased to 9.0 and 10.0, KEGG enrichment analysis showed that photosynthesis (map00195) and nitrogen metabolism (map00910) were significantly enriched (P