title: The chlorophyll-containing orchid Corallorhiza trifida derives little carbon through photosynthesis.
abstract: While measurements of tissue stable isotope signatures and isotope mixing models have suggested that the green orchid Corallorhiza trifida is photosynthetically active and hence only partially mycoheterotrophic, these assumptions have not been validated by direct analysis of carbon assimilation. The photosynthetic capabilities of three orchid species assumed on the basis of the indirect methods or chlorophyll content to have differing trophic strategies: Neottia nidus-avis (fully mycoheterotrophic), Cephalanthera damasonium (partially autotrophic), C. trifida (partially autotrophic), as well as saplings of an autotrophic tree, Fagus sylvatica, were investigated by combining the determination of chlorophyll content and fluorescence, with direct measurement of the potential for CO(2) assimilation using (13)C isotope tracers in the field. Chlorophyll content and fluorescence values were indicative of ineffective photochemical processes in Neottia and reduced efficiency of photochemical processes in Corallorhiza. These differences are reflected in the mean assimilation rates of (13)CO(2) of 594 +/- 129, 331 +/- 72, 12.4 +/- 2.4 and 7.3 +/- 0.9 microg g(-1) h(-1) for Fagus, Cephalanthera, Corallorhiza and Neottia, respectively. Our study, while confirming the fully mycoheterotrophic status of Neottia and the partially autotrophic condition in Cephalanthera, also demonstrates under field conditions that Corallorhiza is physiologically closer to the fully mycoheterotrophic condition than has previously been recognized.
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Alfred Denny Building, Western Bank, Sheffield, S10 2TN, UK.
authors.forename: Duncan D
authors.initials: DD
authors.lastname: Cameron
authors.affiliation: BayCEER - Laboratory of Isotope Biogeochemistry, University of Bayreuth Universitätsstrasse 30, D-95440 Bayreuth, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Preiss
authors.affiliation: BayCEER - Laboratory of Isotope Biogeochemistry, University of Bayreuth Universitätsstrasse 30, D-95440 Bayreuth, Germany.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Gebauer
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Alfred Denny Building, Western Bank, Sheffield, S10 2TN, UK.
authors.forename: David J
authors.initials: DJ
authors.lastname: Read
mesh_terms: D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D002247:Carbon Isotopes; D002734:Chlorophyll / Q000378:metabolism*; D005453:Fluorescence; D029595:Orchidaceae / Q000378:metabolism*; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D002245:Carbon Dioxide; D002244:Carbon