title: Plant growth depressions in arbuscular mycorrhizal symbioses: not just caused by carbon drain?
abstract: * 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.
authors.affiliation: Soil and Land Systems, School of Earth and Environmental Sciences, Waite Campus, University of Adelaide, Adelaide, South Australia 5005, Australia.
authors.forename: Huiying
authors.initials: H
authors.lastname: Li
authors.affiliation: Soil and Land Systems, School of Earth and Environmental Sciences, Waite Campus, University of Adelaide, Adelaide, South Australia 5005, Australia.
authors.forename: F Andrew
authors.initials: FA
authors.lastname: Smith
authors.affiliation: Soil and Land Systems, School of Earth and Environmental Sciences, Waite Campus, University of Adelaide, Adelaide, South Australia 5005, Australia.
authors.forename: Sandy
authors.initials: S
authors.lastname: Dickson
authors.affiliation: Soil and Land Systems, School of Earth and Environmental Sciences, Waite Campus, University of Adelaide, Adelaide, South Australia 5005, Australia.|Minnipa Agricultural Centre, South Australian Research and Development Institute, PO Box 31, Minnipa, South Australia 5654, Australia.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Holloway
authors.affiliation: Soil and Land Systems, School of Earth and Environmental Sciences, Waite Campus, University of Adelaide, Adelaide, South Australia 5005, Australia.
authors.forename: Sally E
authors.initials: SE
authors.lastname: Smith
mesh_terms: D002244:Carbon / Q000378:metabolism*; D025301:Hyphae / Q000502:physiology; D038821:Mycorrhizae / Q000254:growth & development / Q000502:physiology*; D010758:Phosphorus; D018517:Plant Roots / Q000378:metabolism / Q000382:microbiology; D018520:Plant Shoots / Q000378:metabolism / Q000382:microbiology; D013559:Symbiosis; D014908:Triticum / Q000254:growth & development* / Q000382:microbiology*
chemical_list: D010758:Phosphorus; D002244:Carbon