Effects of bio-based compound amendments on Na+, Ca2+, Mg2+, and K+ distribution in salt-tolerant alfalfa (Medicago sativa L.) grown in saline soils from two regions

Ionic stress in saline soils has been demonstrated to result in a continuous decline in the quality and yield of alfalfas. Despite the widespread application of numerous soil amendments in saline soils management, the efficacy and general applicability of these novel amendments in mitigating ionic stress in alfalfas remains to be elucidated. To address this, bio-based compound amendments (BF), comprising earthworm manure, active enzyme treatments, and endophytic mycorrhizal fungi, were tested on two saline soils from the northern Jiangsu tidal flat (JS) and the Yellow River Delta (SD). The soils were treated with no amendments (CK) or BF in alfalfa potting experiments. We evaluated the effects of BF on alfalfa growth, as well as on the uptake, transport, and distribution of Na+, Ca2+, Mg2+, and K+, in the roots, stems, and leaves of alfalfa. BF application significantly increased aboveground and root dry weight of alfalfa on JS soils by 39.20% and 67.10%, respectively, and on SD soils by 78.38% and 45.58%, compared to CK. Additionally, BF application resulted in a significant decrease in Na+ concentration in stems and leaves and increased K+ concentration in all organs of alfalfa grown on both JS and SD saline soils. Applying BF also resulted in a significant increase in K+/Na+ ratios and Ca2+/Na+ transport selectivity ratios in each organ of alfalfa grown in JS and SD saline soils. However, in JS saline soils, BF application resulted in an increase in Mg2+ translocation from roots to stems and a decrease in translocation from stems to leaves. In contrast, the opposite was observed in SD. Overall, the application of BF can enhance the selective absorption and transportation of K+, Ca2+, and Mg2+ grown in JS and SD saline soils, inhibit the selective absorption and transportation of Na+ in alfalfa, maintain the balance of ion metabolism within the plant, and improve the nutritional status and salt tolerance of alfalfas, which is an effective method for improving saline soil and promoting the growth quality of alfalfas.