AOBPreview originally published online on July 25, 2008
Annals of Botany 2009 103(2):303-312; doi:10.1093/aob/mcn120
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Tolerance of combined submergence and salinity in the halophytic stem-succulent Tecticornia pergranulata
1 School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
2 Plant Ecophysiology, Faculty of Biology, Utrecht University, Sorbonnelaan 16, 3584 CA, Utrecht, The Netherlands
3 Freshwater Biological Laboratory, Biological Institute, University of Copenhagen, Helsingørsgade 51, DK-3400 Hillerød, Denmark
* For correspondence. E-mail opedersen{at}bi.ku.dk
Received: 31 March 2008 Returned for revision: 12 May 2008 Accepted: 2 June 2008 Published electronically: 25 July 2008
Background and Aims: Habitats occupied by many halophytes are not only saline, but are also prone to flooding. Few studies have evaluated submergence tolerance in halophytes.
Methods: Responses to submergence, at a range of salinity levels, were studied for the halophytic stem-succulent Tecticornia pergranulata subsp. pergranulata (syn. Halosarcia pergranulata subsp. pergranulata). Growth and total sugars in succulent stems were assessed as a function of time after submergence. Underwater net photosynthesis, dark respiration, total sugars, glycinebetaine, Na+, Cl– and K+, in succulent stems, were assessed in a NaCl dose-response experiment.
Key Results: Submerged plants ceased to grow, and tissue sugars declined. Photosynthesis by succulent stems was reduced markedly when underwater, as compared with in air. Capacity for underwater net photosynthesis (PN) was not affected by 10–400 mM NaCl, but it was reduced by 30 % at 800 mM. Dark respiration, underwater, increased in succulent stems at 200–800 mM NaCl, as compared with those at 10 mM NaCl. On an ethanol-insoluble dry mass basis, K+ concentration in succulent stems of submerged plants was equal to that in drained controls, across all NaCl treatments. Na+ and Cl– concentrations, however, were elevated in stems of submerged plants, but so was glycinebetaine. Submerged stems increased in succulence, so solutes would have been ‘diluted’ on a tissue-water basis.
Conclusions: Tecticornia pergranulata tolerates complete submergence, even in waters of high salinity. A ‘quiescence response’, i.e. no shoot growth, would conserve carbohydrates, but tissue sugars still declined with time. A low K+ : Na+ ratio, typical for tissues of succulent halophytes, was tolerated even during prolonged submergence, as evidenced by maintenance of underwater PN at up to 400 mM NaCl. Underwater PN provides O2 and sugars, and thus should enhance survival of submerged plants.
Key words: Flooding, halophyte, Halosarcia pergranulata, inundation, inland salt marsh, respiration, Salicornioideae, salt lake, submergence–salinity interaction, tissue solutes, underwater net photosynthesis
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