Nutrient Cycling in Agroecosystems

, Volume 63, Issue 1, pp 35–42 | Cite as

The application of isotopic (32P and 15N) dilution techniques to evaluate the interactive effect of phosphate-solubilizing rhizobacteria, mycorrhizal fungi and Rhizobium to improve the agronomic efficiency of rock phosphate for legume crops

  • J.M. BareaEmail author
  • M. Toro
  • M.O. Orozco
  • E. Campos
  • R. Azcón


A pot experiment was designed to evaluate the interactive effects of multifunctional microbial inoculation treatments and rock phosphate (RP) application on N and P uptake by alfalfa through the use of 15N and 32P isotopic dilution approaches. The microbial inocula consisted of a wild type (WT) Rhizobium meliloti strain, the arbuscular mycorrhizal (AM) fungus Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe, and a phosphate solubilizing rhizobacterium (Enterobacter sp.). Inoculated microorganisms were established in the root tissues and/or in the rhizosphere soil of alfalfa plants (Medicago sativa L.). Improvements in N and P accumulation in alfalfa corroborate beneficial effects of Rhizobium and AM interactions. Inoculation with selected rhizobacteria improved the AM effect on N or P accumulation in both the RP-added soil and in the non RP-amended controls. Measurements of the 15N/14N ratio in plant shoots indicate an enhancement of the N2 fixation rates in Rhizobium-inoculated AM-plants, over that achieved by Rhizobium in non-mycorrhizal plants. Whether or not RP was added, AM-inoculated plants showed a lower specific activity (32P/31P) than did their comparable non-mycorrhizal controls, suggesting that the plant was using otherwise unavailable P sources. The phosphate-solubilizing, AM-associated, microbiota could in fact release phosphate ions, either from the added RP or from the indigenous ``less-available'' soil phosphate. A low Ca concentrations in the test soil may have benefited P solubilization. Under field conditions, the inoculation with AM fungi significantly increased plant biomass and N and P accumulation in plant tissues. Phosphate-solubilizing rhizobacteria improved mycorrhizal responses in soil dually receiving RP and organic matter amendments. Organic matter addition favoured RP solubilization. This, together with a tailored microbial inoculation, increased the agronomic efficiency of RP in the test soil that was Ca deficient at neutral pH.

Arbuscular mycorrhiza 1532phosphate solubilizing rhizobacteria Rhizobium rock phosphate 


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Copyright information

© Kluwer Academic Publishers 2002

Authors and Affiliations

  • J.M. Barea
    • 1
    Email author
  • M. Toro
    • 1
  • M.O. Orozco
    • 3
  • E. Campos
    • 2
  • R. Azcón
    • 1
  1. 1.Departamento de Microbiología del Suelo y Sistemas SimbióticosSpain
  2. 2.Departamento de Ciencias de la Tierra y Química Ambiental Estación Experimental del Zaidín (CSIC)GranadaSpain
  3. 3.Instituto de Sistemática y EcologíaAcademia Cubana de CienciasHabanaCuba

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