Abstract Detail

Symbioses: Plant, Animal, and Microbe Interactions

Kent, Oliver J [1], Leake, Jonathan, R. [1], Cameron, Duncan D [1].

Effects of light irradiance and sugar concentrations on Goodyera repens and its mycorrhizal symbiont.

Mycorrhizal associations are traditionally viewed as a mutualistic symbiosis between plant roots and soil fungi, encompassing the vast majority of plant species. In this conventional view of symbiosis carbon from plant photosynthates are exchanged for fungal-acquired mineral nutrients from the soil. Orchids are unusual as they produce tiny dust like seeds that are unable to germinate unaided, as a consequence they rely on their fungal partner to supply carbon and mineral nutrients in a form of nutrition known as mycoheterortophy. After several years underground, most orchids subsequently produce green shoots capable of photosynthesis. Recent research employing stable and radio-isotope tracers have shown that once green the orchid can engage in a convential mutalistic symbiosis, exchanging carbon from the plant to the fungus in return for mineral nutrients. Therefore there is a change in carbon nutrition from the mycoheterotrophic seedling to the autotrophic adult green orchid. We investigated whether this conversion to autotrophy is permanent in the adult green orchid or can the orchid switch from autotrophy to mycoheterotrophy when required? Using a microcosm approach we investigated the effects of varying light irradiances and carbon concentrations on the adult green orchid Goodyera repens and its fungal symbiont. We examined if G. repens can obtain carbon from its fungal symbiont in addition to whether the orchid supplies carbon from photosynthesis to its fungal partner. These microcosms were simultaneously dual labelled using ¹⁴C- labelled glucose to measure fungus to plant transfer and ¹³CO₂ to measure plant to fungus transfer. We show that once green G. repens can no longer survive only on fungal carbon, since G. repens cannot increase the carbon acquired from the fungus in low light irradiance and when the fungus is supplied with a high carbon concentration. This shows for the first time that the adult G. repens plant cannot change its trophic strategy (in the short term) once it has become autotrophic.

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1 - University of Sheffield, Department of Animal and Plant Sciences, Alfred Denny Building, Western Bank, Sheffield, South Yorkshire, S10 2TN, UK

Keywords:
Symbioses
Mycorrhiza
orchid
mycoheterotrophy
Goodyera repens.

Presentation Type: Oral Paper:Papers for Topics
Session: 42
Location: 552A/Convention Center
Date: Tuesday, August 3rd, 2010
Time: 2:15 PM
Number: 42004
Abstract ID:172