title: Heat stress of two tropical seagrass species during low tides - impact on underwater net photosynthesis, dark respiration and diel in situ internal aeration.
abstract: Seagrasses grow submerged in aerated seawater but often in low O2 sediments. Elevated temperatures and low O2 are stress factors. Internal aeration was measured in two tropical seagrasses, Thalassia hemprichii and Enhalus acoroides, growing with extreme tides and diel temperature amplitudes. Temperature effects on net photosynthesis (PN ) and dark respiration (RD ) of leaves were evaluated. Daytime low tide was characterized by high pO2 (54 kPa), pH (8.8) and temperature (38°C) in shallow pools. As PN was maximum at 33°C (9.1 and 7.2 μmol O2  m(-2) s(-1) in T. hemprichii and E. acoroides, respectively), the high temperatures and reduced CO2 would have diminished PN , whereas RD increased (Q10 of 2.0-2.7) above that at 33°C (0.45 and 0.33 μmol O2  m(-2)  s(-1) , respectively). During night-time low tides, O2 declined resulting in shoot base anoxia in both species, but incoming water containing c. 20 kPa O2 relieved the anoxia. Shoots exposed to 40°C for 4 h showed recovery of PN and RD , whereas 45°C resulted in leaf damage. These seagrasses are 'living near the edge', tolerant of current diel O2 and temperature extremes, but if temperatures rise both species may be threatened in this habitat.
authors.affiliation: Freshwater Biological Laboratory, Department of Biology, University of Copenhagen, Universitetsparken 4, 3rd floor, 2100, Copenhagen, Denmark.|School of Plant Biology, The University of Western Australia, Crawley, WA, 6009, Australia.|Institute of Advanced Studies, The University of Western Australia, Crawley, WA, 6009, Australia.
authors.forename: Ole
authors.initials: O
authors.lastname: Pedersen
authors.affiliation: School of Plant Biology, The University of Western Australia, Crawley, WA, 6009, Australia.
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Colmer
authors.affiliation: Freshwater Biological Laboratory, Department of Biology, University of Copenhagen, Universitetsparken 4, 3rd floor, 2100, Copenhagen, Denmark.
authors.forename: Jens
authors.initials: J
authors.lastname: Borum
authors.affiliation: School of Plant Biology, The University of Western Australia, Crawley, WA, 6009, Australia.|Oceans Institute, The University of Western Australia, Crawley, WA, 6009, Australia.|Western Australian Marine Science Institution (WAMSI), Crawley, WA, 6009, Australia.
authors.forename: Andrea
authors.initials: A
authors.lastname: Zavala-Perez
authors.affiliation: School of Plant Biology, The University of Western Australia, Crawley, WA, 6009, Australia.|Oceans Institute, The University of Western Australia, Crawley, WA, 6009, Australia.|Western Australian Marine Science Institution (WAMSI), Crawley, WA, 6009, Australia.
authors.forename: Gary A
authors.initials: GA
authors.lastname: Kendrick
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D003624:Darkness; D017753:Ecosystem; D006358:Hot Temperature; D031321:Hydrocharitaceae / Q000502:physiology* / Q000528:radiation effects; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis; D018515:Plant Leaves / Q000502:physiology / Q000528:radiation effects; D012623:Seawater; D013312:Stress, Physiological
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen
keywords: Enhalus acoroides; Thalassia hemprichii; anaerobiosis; anoxia; submerged plants; temperature stress; thermal stress; water column and tissue O2