title: Use of sediment CO2 by submersed rooted plants.
abstract: OBJECTIVE
  Submersed plants have different strategies to overcome inorganic carbon limitation. It is generally assumed that only small rosette species (isoetids) are able to utilize the high sediment CO(2) availability. The present study examined to what extent five species of submersed freshwater plants with different morphology and growth characteristics (Lobelia dortmanna, Lilaeopsis macloviana, Ludwigia repens, Vallisneria americana and Hydrocotyle verticillata) are able to support photosynthesis supplied by uptake of CO(2) from the sediment.
  
  
  METHODS
  Gross photosynthesis was measured in two-compartment split chambers with low inorganic carbon availability in leaf compartments and variable CO(2) availability (0 to >8 mmol L(-1)) in root compartments. Photosynthetic rates based on root-supplied CO(2) were compared with maximum rates obtained at saturating leaf CO(2) availability, and (14)C experiments were conducted for two species to localize bottlenecks for utilization of sediment CO(2).
  
  
  RESULTS
  All species except Hydrocotyle were able to use sediment CO(2), however, with variable efficiency, and with the isoetid, Lobelia, as clearly the most effective and the elodeid, Ludwigia, as the least efficient. At a water column CO(2) concentration in equilibrium with air, Lobelia, Lilaeopsis and Vallisneria covered >75% of their CO(2) requirements by sediment uptake, and sediment CO(2) contributed substantially to photosynthesis at water CO(2) concentrations up to 1000 micromol L(-1). For all species except Ludwigia, the shoot to root ratio on an areal basis was the single factor best explaining variability in the importance of sediment CO(2). For Ludwigia, diffusion barriers limited uptake or transport from roots to stems and transport from stems to leaves.
  
  
  CONCLUSIONS
  Submersed plants other than isoetids can utilize sediment CO(2), and small and medium sized elodeids with high root to shoot area in particular may benefit substantially from uptake of sediment CO(2) in low alkaline lakes.
authors.affiliation: Freshwater Biological Laboratory, Biological Institute, University of Copenhagen, Helsingørsgade 51, Hillerød, Denmark.
authors.forename: Anders
authors.initials: A
authors.lastname: Winkel
authors.forename: Jens
authors.initials: J
authors.lastname: Borum
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D002250:Carbon Radioisotopes; D019015:Geologic Sediments; D029746:Lobelia / Q000254:growth & development / Q000378:metabolism; D019684:Magnoliopsida / Q000254:growth & development / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism*; D018520:Plant Shoots / Q000254:growth & development / Q000378:metabolism
chemical_list: D002250:Carbon Radioisotopes; D002245:Carbon Dioxide