Functional diversity in arbuscular mycorrhizal (AM) symbioses: the contribution of the mycorrhizal P uptake pathway is not correlated with mycorrhizal responses in growth or total P uptake

Authors

  • Sally E. Smith,

    Corresponding author
    1. Centre for Soil–Plant Interactions, Soil and Land Systems, School of Earth and Environmental Sciences, Waite Campus, The University of Adelaide, South Australia, Australia, 5005;
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  • F. Andrew Smith,

    1. Centre for Soil–Plant Interactions, Soil and Land Systems, School of Earth and Environmental Sciences, Waite Campus, The University of Adelaide, South Australia, Australia, 5005;
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  • Iver Jakobsen

    1. Plant Research Department, Risø National Laboratory, PO Box 49, DK-4000 Roskilde, Denmark
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Author for correspondence: Sally E. Smith Tel: +61 (8) 83036704 Fax: +61 (8) 83036511 Email: sally.smith@adelaide.edu.au

Summary

  • • We investigated structural and functional diversity in arbuscular mycorrhizal (AM) symbioses involving three plant species and three AM fungi and measured contributions of the fungi to P uptake using compartmented pots and 33P. The plant/fungus combinations varied in growth and P responses. Flax (Linum usitatissimum) responded positively to all fungi, and medic (Medicago truncatula) to Glomus caledonium and G. intraradices, but not Gigaspora rosea. Tomato (Lycopersicon esculentum) showed no positive responses.
  • • Hyphal growth in soil was very low for Gi. rosea and high for both Glomus spp. Hyphal lengths in root + hyphal compartment (RHC) and hyphal compartment (HC) were similar for G. intraradices, but much higher in HC for G. caledonium.
  • • Specific activities of 33P in plants and soil indicated that fungal P uptake made substantial contributions to five plant/fungus combinations and significant contributions to a further two. G. intraradices delivered close to 100% of the P in all three plants. G. caledonium and Gi. rosea delivered less P. The amount was not related to colonisation or to growth or P responses.
  • • We conclude that: AM colonisation can result in complete inactivation of the direct P uptake pathway via root hairs and epidermis; calculations of AM contributions to P uptake from total plant P will often be highly inaccurate; and lack of plant responsiveness does not mean that an AM fungus makes no contribution to P uptake.

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