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Li J.,Gansu Agricultural University | Li J.,Key Laboratory of Grassland Ecosystem of Ministry of Education | Li J.,Sino Us Centers For Grazing Land Ecosystem Sustainability | Zhang S.,Gansu Agricultural University | And 10 more authors.
Journal of Biobased Materials and Bioenergy

Phosphorus (P) solubilizing and mineralizing soil microorganisms (PSMs) which effectively release P from inorganic and organic pools of total soil P have potential to improve plant yield and reduce fertilizer costs, especially for important leguminous forages like alfalfa. An evaluation program was undertaken in Gansu Province, China to select naturally occurring nitrogen (N) fixing and P solubilizing Rhizobium strains extracted from nodules collected from eight alfalfa (Medicago sativa L.) cultivars. Colony morphology, standard diagnostic tests (both physiological and biochemical) and inoculation onto alfalfa seed (cv. Longdong) were used to identify Rhizobium strains from other PSMs and compare their responses to standard non-P solubilizing (Sinorhizobium meliloti 12531) and P-solubilizing (Rhizobium. meliloti SL01) controls. From the 41 largest colonies exhibiting N-fixing capacity isolated from alfalfa nodules, only 5 PSMs were identified with capacity to solubilise from Ca 3(PO4)2 as the sole P source. Diagnostic tests showed similarity between these isolates in carbon source utilization and a failure to produce 3-ketolactose but only two isolates (L-5 and L-7) produced negative reactions to starch and citrate utilization and a positive catalase test confirming that they belong to the Rhizobium genus. L-5 and L-7 were the only isolates to produce nodules similar to the controls. L-5 and L-7 exhibited a capacity to solubilize inorganic P 1.2 to 1.9 times greater than the control strain R. meliloti SL01 under in vitro conditions. Auxin secretion was higher in L-5 resulted in higher salt tolerance, more significant nodule production and higher nitrogenase activity than L-7 and the standard inoculant S. meliloti 12531 which indicate that L-5 may provide good source material for engineering new strains with an increased capacity for P solubilization. Copyright © 2012 American Scientific Publishers. Source

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