title: Symbiont abundance can affect host plant population dynamics.
abstract: OBJECTIVE
  Symbioses are almost universal, but little is known about how symbiont abundance can affect host performance. Many orchids undergo vegetative dormancy and frequent and protracted dormancy have been associated with population declines. If mycorrhizal fungi affect host plant performance, those effects are likely to alter patterns of vegetative dormancy. The goal of this study was to determine whether the abundance of mycorrhizal fungi is related to the likelihood of entering dormancy and whether fungal abundance varied with dormancy duration in the federally listed threatened orchid Isotria medeoloides.
  
  
  METHODS
  We studied three populations of the threatened North American terrestrial orchid Isotria medeoloides using long-term emergence data and evaluated the relationship between the abundance of associated mycorrhizal fungi (Russulaceae) and orchid dormancy and emergence. Mycorrhizal fungi in soil adjacent to orchids were quantified in two ways. First, ectomycorrhizal (ECM) fungi on adjacent root tips were identified using DNA sequencing to determine their phylogenetic relationship to fungi that are known to form mycorrhizae with I. medeoloides. Second, we extracted DNA from soil samples and used quantitative real-time PCR to estimate the abundance of Russulaceae hyphae adjacent to each orchid.
  
  
  RESULTS
  We found that the abundance of Russulaceae, both in the soil and on nearby ECM root tips, was significantly related to orchid prior emergence. Both abundance and prior emergence history were predictive of future emergence.
  
  
  CONCLUSIONS
  These results suggest that the abundance of mycorrhizal fungi can influence orchid population dynamics and is an essential component of orchid conservation.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, Connecticut 06269-3043 USA.
authors.forename: Rachel
authors.initials: R
authors.lastname: Rock-Blake
authors.affiliation: Smithsonian Environmental Research Center, P. O. Box 28, Edgewater, Maryland 21037 USA mccormickm@si.edu.
authors.forename: Melissa K
authors.initials: MK
authors.lastname: McCormick
authors.affiliation: Smithsonian Environmental Research Center, P. O. Box 28, Edgewater, Maryland 21037 USA.
authors.forename: Hope E A
authors.initials: HE
authors.lastname: Brooks
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, Connecticut 06269-3043 USA.
authors.forename: Cynthia S
authors.initials: CS
authors.lastname: Jones
authors.affiliation: Smithsonian Environmental Research Center, P. O. Box 28, Edgewater, Maryland 21037 USA.
authors.forename: Dennis F
authors.initials: DF
authors.lastname: Whigham
mesh_terms: D001487:Basidiomycota / Q000145:classification / Q000235:genetics / Q000502:physiology*; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics; D025301:Hyphae / Q000235:genetics / Q000502:physiology; D038821:Mycorrhizae / Q000145:classification / Q000235:genetics / Q000502:physiology*; D029595:Orchidaceae / Q000382:microbiology* / Q000502:physiology; D010802:Phylogeny; D057445:Plant Dormancy; D018517:Plant Roots / Q000382:microbiology; D017422:Sequence Analysis, DNA; D012988:Soil Microbiology; D013045:Species Specificity; D013559:Symbiosis / Q000502:physiology*
chemical_list: D004271:DNA, Fungal
keywords: Isotria medeoloides; Orchidaceae; Russula; dormancy; mycorrhizal fungi; orchid