Plant growth depressions in arbuscular mycorrhizal symbioses: not just caused by carbon drain?

Authors

  • Huiying Li,

    1. Soil and Land Systems, School of Earth and Environmental Sciences, Waite Campus, University of Adelaide, Adelaide, South Australia 5005, Australia;
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  • F. Andrew Smith,

    1. Soil and Land Systems, School of Earth and Environmental Sciences, Waite Campus, University of Adelaide, Adelaide, South Australia 5005, Australia;
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  • Sandy Dickson,

    1. Soil and Land Systems, School of Earth and Environmental Sciences, Waite Campus, University of Adelaide, Adelaide, South Australia 5005, Australia;
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  • Robert E. Holloway,

    1. Soil and Land Systems, School of Earth and Environmental Sciences, Waite Campus, University of Adelaide, Adelaide, South Australia 5005, Australia;
    2. Minnipa Agricultural Centre, South Australian Research and Development Institute, PO Box 31, Minnipa, South Australia 5654, Australia
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  • Sally E. Smith

    1. Soil and Land Systems, School of Earth and Environmental Sciences, Waite Campus, University of Adelaide, Adelaide, South Australia 5005, Australia;
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Author for correspondence:
F. Andrew Smith
Tel: +61 8 83036517
Fax: +61 8 83036511
Email:andrew.smith@adelaide.edu.au

Summary

  • • This study investigated effects of plant density and arbuscular mycorrhizal (AM) colonization on growth and phosphorus (P) nutrition of a cultivar of wheat (Triticum aestivum) that often shows early AM-induced growth depressions.
  • • Two experiments were conducted. Expt 1 had three plant densities and one soil P concentration. Expt 2 had two plant densities and two P concentrations. Plants were grown in calcareous P-fixing soil, inoculated with Glomus intraradices or Gigaspora margarita, or noninoculated (nonmycorrhizal (NM)). Glomus intraradices colonized well and caused a growth depression only in Expt 1. Gigaspora margarita caused large growth depressions in both experiments even though it colonized poorly.
  • • The results showed that growth depressions were mitigated by changes in relative competition for soil P by NM and AM plants, and probably by decreasing carbon costs of the fungi.
  • • The different effects of the two fungi appear to be attributable to differences in the balance between P uptake by the fungal pathway and direct uptake via the roots. These differences may be important in other AM symbioses that result in growth depressions. The results show that mycorrhizal growth responses of plants grown singly may not apply at the population or community level.

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