Ca2+/Na+ Ratio as a Critical Marker for Field Evaluation of Saline-Alkaline Tolerance in Alfalfa (Medicago sativa L.)

Abstract

Current indices of saline-alkaline (SA) tolerance are mainly based on the traditional growth and physiological indices for salinity tolerance and likely affect the accuracy of alfalfa tolerance predictions. We determined whether the inclusion of soil alkalinity-affected indices, particularly Ca2+, Mg2+, and their ratios to Na+ in plants, based on the traditional method could improve the prediction accuracy of SA tolerance in alfalfa, determine important indices for SA tolerance, and identify suitable alfalfa cultivars in alkaline salt-affected soils. Fifty alfalfa cultivars were evaluated for their SA tolerance under SA and non-SA field conditions. The SA-tolerance coefficient (SATC) for each investigated index of the alfalfa shoot was calculated as the ratio of SA to non-SA field conditions, and the contribution of SATC under different growth and physiological indices to SA tolerance was quantified based on the inclusion/exclusion of special alkalinity-affected indices. The traditional method, excluding the special alkalinity-affected indices, explained nearly all of the variation in alfalfa SA tolerance, and the most important predictor was the SATC of stem length. The new method, which included these special alkalinity-affected indices, had similar explanatory power but instead identified the SATC of shoot Ca2+/Na+ ratio, followed by that of stem length, as key markers for the field evaluation of SA tolerance. Ca2+, Mg2+, and their ratios to Na+ hold promise for enhancing the robustness of SA-tolerance predictions in alfalfa. These results encourage further investigation into the involvement of Ca2+ in such predictions in other plant species and soil types under more alkaline salt-affected conditions.

Physiological and transcriptomic analyses reveal novel insights into the cultivar-specific response to alkaline stress in alfalfa (Medicago sativa L.)

“…Alkaline stress not only inhibits the seed germination of alfalfa but also seriously affects the growth and development of seedlings (An et al 2016, Liu et al 2018, Long et al 2019. Our previous study also con rmed that the alkaline tolerance of alfalfa was associated with the cultivar's genetic characteristics (Wei et al 2020). As shown by our results, AG is more sensitive to alkaline stress than GN, as re ected by the decreased shoot fresh weight and leaf chlorophyll contents (Fig.…”

“…3). Interestingly, GN maintained higher accumulation of Ca 2+ and Mg 2+ , and the ratios of these two ions to Na + in shoots were also higher than those in AG, suggesting that accumulation pro les of Ca 2+ and Mg 2+ may play an important role in maintaining ionic homeostasis in alfalfa under alkaline stress (Wei et al 2020). Based on the above results, we speculate that the transient increase in Ca 2+ levels of alkalinetreated plants might activate alkaline signaling pathways in the plant and be involved in regulating anti-stress genes expressed in response to alkaline stress.…”

“…Plant material and alkaline-stress treatment An alkaline-tolerant cultivar, Gongnong NO.1 (GN), and an alkaline-sensitive cultivar, Algonquin (AG), were selected based on our previous study (Wei et al 2020). The seeds were sterilized with a solution containing 6% sodium hypochlorite for 10 min and rinsed with distilled water three times.…”

“…As GN had higher tolerance to alkaline stress than AG (Wei et al 2020; Fig. 1), we hypothesized that the DEGs mapped to signi cant enrichment categories or speci c enrichment in GN may contribute to the alkaline tolerance phenotype of alfalfa.…”

Genome-wide identification, phylogeny and expression analysis of the SPL gene family and its important role in salt stress in Medicago sativa L.

“…In China, most alfalfa plantations are located in regions with saline-alkali soil due to the lack of farmland [ 44 ]. An urgent and promising task for alfalfa production in the nation is to breed varieties with tolerance to high salinity [ 45 ]. Our prediction of the cis -elements present in the putative promoter region of the MsSPLs revealed that 89.4% of MsSPLs possessed ABA-responsive elements (ABREs) [ 46 ], suggesting a possible contribution to the alfalfa abiotic stress response.…”