o:7020 The Plant Growth-Promoting Ability of Alfalfa Rhizobial Strains Under Nickel Stress en Abstract: The growth and nutrient balance of legumes can be disrupted in soils with increased nickel (Ni) concentrations. The inoculation of legumes with rhizobia, symbiotic nitrogen-fixing bacteria, can be used for the alleviation of trace metal stress in plants. This study evaluated the Ni tolerance of alfalfa rhizobia isolates and some plant growthpromoting traits in the presence of Ni: indole-3-acetic acid (IAA) production, Ni biosorption potential, and the effect of rhizobia on alfalfa (Medicago sativa L.) growth. The strains were characterized as Shinorhizobium meliloti, Sinorhizobium medicae, and Rhizobium tibeticum. In total, 70% of the tested strains tolerate up to 0.8 mM Ni, while 15% of the strains tolerate 1.2 mM Ni. The production of IAA was maintained in the presence of Ni until bacterial growth was stopped by raising the Ni concentration. Alfalfa seed germination is significantly reduced in the presence of 0.5 mM Ni, while a significant reduction in 10-day-old seedling length already occurs at a Ni concentration of 0.03 mM. In the plant experiment, when alfalfa was inoculated with rhizobial strains, nodulation was maintained up to 0.05 mM Ni, but a significant reduction in nodule number was detected at 0.01 mM Ni. At the concentration of 0.005 mM Ni, inoculation with 12 particular rhizobial strains significantly improved the number of nodules per plant, plant height, and root length, as well as plant shoot dry weight, compared to non-inoculated plants with Ni addition. However, higher concentrations caused a reduction in all of these plant growth parameters compared to the plants without Ni. The selected rhizobia strains showed a Ni biosorption capacity of 20% in the in vitro assay. The inoculation of alfalfa with effective rhizobial strains improves growth parameters compared to non-inoculated plants in the presence of certain concentrations of Ni. Medicago sativa; Sinorhizobium; trace metals; nickel; plant growth promotion 1552099 10.3390/ microorganisms13020340 2025-02-10T07:00:14.148Z 44 no 46 Mila Pešić Institute of Soil Science 0000-0001-7589-9100 46 Sonja Tošić Jojević Institute of Soil Science 0000-0002-3865-6529 46 Biljana Sikirić Institute of Soil Science 0000-0002-8308-4582 46 Vesna Mrvić Institute of Soil Science 0000-0002-6666-0875 46 Marina Jovković Institute of Soil Science 0000-0001-7224-8556 46 Mira Milinković Institute of Soil Science 0000-0001-5175-6842 46 Snežana Andjelković Institute for Forage Crops Kruševac 0000-0003-0436-3530 46 Olivera Stajković-Srbinović Institute of Soil Science 0000-0001-9759-843X application/pdf 2800088 https://unilib.phaidrabg.rs/o:7020 no yes 1 70 92000001 71A05 Microorganisms 13, 340 2025