title: Mycorrhizas alter nitrogen acquisition by the terrestrial orchid Cymbidium goeringii.
abstract: OBJECTIVE
  Orchid mycorrhizas exhibit a unique type of mycorrhizal symbiosis that occurs between fungi and plants of the family Orchidaceae. In general, the roots of orchids are typically coarse compared with those of other plant species, leading to a considerably low surface area to volume ratio. As a result, orchids are often ill-adapted for direct nutrient acquisition from the soil and so mycorrhizal associations are important. However, the role of the fungal partners in the acquisition of inorganic and organic N by terrestrial orchids has yet to be clarified.
  
  
  METHODS
  Inorganic and amino acid N uptake by non-mycorrhizal and mycorrhizal Cymbidium goeringii seedlings, which were grown in pots in a greenhouse, was investigated using a (15)N-labelling technique in which the tracer was injected at two different soil depths, 2·5 cm or 7·5 cm. Mycorrhizal C. goeringii seedlings were obtained by inoculation with three different mycorrhizal strains isolated from the roots of wild terrestrial orchids (two C. goeringii and one C. sinense).
  
  
  RESULTS
  Non-mycorrhizal C. goeringii primarily took up NO3(-) from tracers injected at 2·5-cm soil depth, whereas C. goeringii inoculated with all three mycorrhiza primarily took up NH4(+) injected at the same depth. Inoculation of the mycorrhizal strain MLX102 (isolated from adult C. sinense) on C. goeringii roots only significantly increased the below-ground biomass of the C. goeringii; however, it enhanced (15)NH4(+) uptake by C. goeringii at 2·5-cm soil depth. Compared to the uptake of tracers injected at 2·5-cm soil depth, the MLX102 fungal strain strongly enhanced glycine-N uptake by C. goeringii from tracers injected at 7·5-cm soil depth. Cymbidium goeringii inoculated with CLB113 and MLX102 fungal strains demonstrated a similar N uptake pattern to tracers injected at 2·5-cm soil depth.
  
  
  CONCLUSIONS
  These findings demonstrate that mycorrhizal fungi are able to switch the primary N source uptake of a terrestrial orchid, in this case C. goeringii, from NO3(-) to NH4(+). The reasons for variation in N uptake in the different soil layers may be due to possible differentiation in the mycorrhizal hyphae of the C. goeringii fungal partner.
authors.affiliation: Key Laboratory of Biodiversity Conservation in Southwest China, State Forestry Administration, Southwest Forestry University, Kunming, China.
authors.forename: Jianrong
authors.initials: J
authors.lastname: Wu
authors.forename: Huancheng
authors.initials: H
authors.lastname: Ma
authors.forename: Xingliang
authors.initials: X
authors.lastname: Xu
authors.forename: Na
authors.initials: N
authors.lastname: Qiao
authors.forename: Shitan
authors.initials: S
authors.lastname: Guo
authors.forename: Fang
authors.initials: F
authors.lastname: Liu
authors.forename: Donghua
authors.initials: D
authors.lastname: Zhang
authors.forename: Liping
authors.initials: L
authors.lastname: Zhou
mesh_terms: D018533:Biomass; D038821:Mycorrhizae / Q000502:physiology*; D009584:Nitrogen / Q000378:metabolism*; D029595:Orchidaceae / Q000254:growth & development / Q000378:metabolism* / Q000382:microbiology
chemical_list: D009584:Nitrogen
keywords: 15N labelling; Cymbidium species; Mycorrhizal fungi; amino acid uptake; nutrient acquisition