title: Oxic microshield and local pH enhancement protects Zostera muelleri from sediment derived hydrogen sulphide.
abstract: Seagrass is constantly challenged with transporting sufficient O₂ from above- to belowground tissue via aerenchyma in order to maintain aerobic metabolism and provide protection against phytotoxins. Electrochemical microsensors were used in combination with a custom-made experimental chamber to analyse the belowground biogeochemical microenvironment of Zostera muelleri under changing environmental conditions. Measurements revealed high radial O₂ release of up to 500 nmol O2 cm(-2) h(-1) from the base of the leaf sheath, maintaining a c. 300-μm-wide plant-mediated oxic microzone and thus protecting the vital meristematic regions of the rhizome from reduced phytotoxic metabolites such as hydrogen sulphide (H₂S). H₂S intrusion was prevented through passive diffusion of O₂ to belowground tissue from leaf photosynthesis in light, as well as from the surrounding water column into the flow-exposed plant parts during darkness. Under water column hypoxia, high belowground H₂S concentrations at the tissue surface correlated with the inability to sustain the protecting oxic microshield around the meristematic regions of the rhizome. We also found increased pH levels in the immediate rhizosphere of Z. muelleri, which may contribute to further detoxification of H₂S through shifts in the chemical speciation of sulphide. Zostera muelleri can modify the geochemical conditions in its immediate rhizosphere, thereby reducing its exposure to H₂S.
authors.affiliation: Plant Functional Biology and Climate Change Cluster, University of Technology Sydney (UTS), 15 Broadway, Ultimo, Sydney, NSW, 2007, Australia.
authors.forename: Kasper Elgetti
authors.initials: KE
authors.lastname: Brodersen
authors.affiliation: Plant Functional Biology and Climate Change Cluster, University of Technology Sydney (UTS), 15 Broadway, Ultimo, Sydney, NSW, 2007, Australia.
authors.forename: Daniel Aagren
authors.initials: DA
authors.lastname: Nielsen
authors.affiliation: Plant Functional Biology and Climate Change Cluster, University of Technology Sydney (UTS), 15 Broadway, Ultimo, Sydney, NSW, 2007, Australia.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Ralph
authors.affiliation: Plant Functional Biology and Climate Change Cluster, University of Technology Sydney (UTS), 15 Broadway, Ultimo, Sydney, NSW, 2007, Australia.|Marine Biological Section, Department of Biology, University of Copenhagen, Strandpromenaden 5, DK-3000, Helsingør, Denmark.|Singapore Centre on Environmental Life Sciences Engineering, School of Biological Sciences, Nanyang Technological University, Singapore.
authors.forename: Michael
authors.initials: M
authors.lastname: Kühl
mesh_terms: D019015:Geologic Sediments / Q000737:chemistry*; D006862:Hydrogen Sulfide / Q000633:toxicity*; D006863:Hydrogen-Ion Concentration; D008954:Models, Biological; D010100:Oxygen / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism; D011789:Quantum Theory; D027343:Rhizome / Q000187:drug effects / Q000378:metabolism; D058441:Rhizosphere; D013050:Spectrometry, Fluorescence; D035962:Zosteraceae / Q000378:metabolism*
chemical_list: D045332:Photosystem II Protein Complex; D010100:Oxygen; D006862:Hydrogen Sulfide
keywords: Zostera muelleri; biogeochemistry; microelectrodes; oxic microshield; plant-sediment interactions; radial oxygen release; rhizosphere