Native Mesorhizobium strains improve yield and nutrient composition of the common bird's-foot trefoil grown in an acid soil

Acid soils occupy more than 3.95 billion ha of the world soils, and finding an adequate solution for the limitation of crop production on these soils is indispensable. Using highly effective rhizobia tolerant to low pH enables successful nodulation and quality crop production of legumes in acid soils. In this study, isolation and characterization of native rhizobia associated with root nodules of bird's-foot trefoil (Lotus corniculatus L.) from Serbia were conducted. Their effects on the plant yield and nutrient composition of bird's-foot trefoil grown in an acid soil (pH 5.4), in a pot experiment were evaluated. Out of 72 strains isolated, 40 could nodulate bird's-foot trefoil when reinoculated in the test tubes under gnotobiotic conditions, and 23 isolates showed high nitrogen-fixing efficiency. Overall, all isolates could grow well in medium with a pH between 4.5 and 8. Indole-3-acetic acid (IAA) production was detected in all nodulating isolates and 24 could solubilize inorganic phosphates. The identification of selected isolates showed that all belong to Mesorhizobium genus (M. tianshanense, M. erdmanii, M. cantuariense, M. loti, M. jarvisii and M. caraganae). Four acid-tolerant isolates (1M12, 631oz, U1C, and 754) with high nitrogen-fixing efficiency in vitro and particular PGP traits were selected for the pot experiment with acid soil. All applied bacterial treatments (except 1M12) increased the shoot dry weight of bird's-foot trefoil plants (up to 50%), compared to the control. In addition, N uptake and N% were increased up to 20% by inoculation. All applied treatments influenced the concentrations and improved uptake of macro (P, K, Ca, and Mg) and micronutrients (Cu, Fe, Mn, Ni, Zn, and B) in the plant material. The obtained results indicated that satisfactory yield and mineral composition of L. corniculatus in acid soils could be achieved by inoculation with selected Mesorhizobium strains.