title: Contrasting submergence tolerance in two species of stem-succulent halophytes is not determined by differences in stem internal oxygen dynamics.
abstract: OBJECTIVE
  Many stem-succulent halophytes experience regular or episodic flooding events, which may compromise gas exchange and reduce survival rates. This study assesses submergence tolerance, gas exchange and tissue oxygen (O2) status of two stem-succulent halophytes with different stem diameters and from different elevations of an inland marsh.
  
  
  METHODS
  Responses to complete submergence in terms of stem internal O2 dynamics, photosynthesis and respiration were studied for the two halophytic stem-succulents Tecticornia auriculata and T. medusa. Plants were submerged in a glasshouse experiment for 3, 6 and 12 d and O2 levels within stems were measured with microelectrodes. Photosynthesis by stems in air after de-submergence was also measured.
  
  
  RESULTS
  Tecticornia medusa showed 100 % survival in all submergence durations whereas T. auriculata did not survive longer than 6 d of submergence. O2 profiles and time traces showed that when submerged in water at air-equilibrium, the thicker stems of T. medusa were severely hypoxic (close to anoxic) when in darkness, whereas the smaller diameter stems of T. auriculata were moderately hypoxic. During light periods, underwater photosynthesis increased the internal O2 concentrations in the succulent stems of both species. Stems of T. auriculata temporally retained a gas film when first submerged, whereas T. medusa did not. The lower O2 in T. medusa than in T. auriculata when submerged in darkness was largely attributed to a less permeable epidermis. The submergence sensitivity of T. auriculata was associated with swelling and rupturing of the succulent stem tissues, which did not occur in T. medusa.
  
  
  CONCLUSIONS
  The higher submergence tolerance of T. medusa was not associated with better internal aeration of stems. Rather, this species has poor internal aeration of the succulent stems due to its less permeable epidermis; the low epidermal permeability might be related to resistance to swelling of succulent stem tissues when submerged.
authors.affiliation: School of Plant Biology and Institute of Advances Studies, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia and Freshwater Biological Laboratory, Institute of Biology, University of Copenhagen, Universitetsparken 4, 2100 Copenhagen, Denmark dennis.konnerup@uwa.edu.au.
authors.forename: Dennis
authors.initials: D
authors.lastname: Konnerup
authors.affiliation: School of Plant Biology and Institute of Advances Studies, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia and Freshwater Biological Laboratory, Institute of Biology, University of Copenhagen, Universitetsparken 4, 2100 Copenhagen, Denmark.
authors.forename: Louis
authors.initials: L
authors.lastname: Moir-Barnetson
authors.affiliation: School of Plant Biology and Institute of Advances Studies, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia and Freshwater Biological Laboratory, Institute of Biology, University of Copenhagen, Universitetsparken 4, 2100 Copenhagen, Denmark School of Plant Biology and Institute of Advances Studies, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia and Freshwater Biological Laboratory, Institute of Biology, University of Copenhagen, Universitetsparken 4, 2100 Copenhagen, Denmark School of Plant Biology and Institute of Advances Studies, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia and Freshwater Biological Laboratory, Institute of Biology, University of Copenhagen, Universitetsparken 4, 2100 Copenhagen, Denmark.
authors.forename: Ole
authors.initials: O
authors.lastname: Pedersen
authors.affiliation: School of Plant Biology and Institute of Advances Studies, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia and Freshwater Biological Laboratory, Institute of Biology, University of Copenhagen, Universitetsparken 4, 2100 Copenhagen, Denmark.
authors.forename: Erik J
authors.initials: EJ
authors.lastname: Veneklaas
authors.affiliation: School of Plant Biology and Institute of Advances Studies, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia and Freshwater Biological Laboratory, Institute of Biology, University of Copenhagen, Universitetsparken 4, 2100 Copenhagen, Denmark.
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Colmer
mesh_terms: D027703:Amaranthaceae / Q000502:physiology*; D055868:Floods; D008027:Light; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis; D018547:Plant Stems / Q000502:physiology; D055049:Salt Tolerance; D013045:Species Specificity; D014904:Western Australia
chemical_list: D010100:Oxygen
keywords: Flooding tolerance; Salicornioideae; Tecticornia auriculata; Tecticornia medusa; gas film; halophyte; oxygen dynamics; samphire.; submergence tolerance; underwater photosynthesis; underwater respiration