title: Photosynthesis in estuarine intertidal microphytobenthos is limited by inorganic carbon availability.
abstract: The effects of dissolved inorganic carbon (DIC) availability on photosynthesis were studied in two estuarine intertidal microphytobenthos (MPB) communities and in the model diatom species Phaeodactylum tricornutum. Kinetics of DIC acquisition, measured with a liquid-phase oxygen electrode, showed higher K(1/2)(DIC) (0.31 mM) and Vm (7.78 nmol min(-1) µg (Chl a)(-1)) for MPB suspensions than for P. tricornutum (K(1/2)(DIC) = 0.23 mM; Vm = 4.64 nmol min(-1) µg (Chl a)(-1)), suggesting the predominance of species with lower affinity for DIC and higher photosynthetic capacity in the MPB. The net photosynthetic rate of the MPB suspensions reached saturation at a DIC concentration of 1-1.5 mM. This range was lower than the concentrations found in the interstitial water of the top 5-mm sediment layer, suggesting no limitation of photosynthesis by DIC in the MPB communities. Accordingly, carbon isotope discrimination revealed a moderate activity of CO2-concentrating mechanisms in the MPB. However, addition of NaHCO3 to intact MPB biofilms caused a significant increase in the relative maximum photosynthetic electron transport rate (rETR max) measured by imaging pulse-amplitude modulated chlorophyll a fluorescence. These results suggest local depletion of DIC at the photic layer of the sediment (the first few hundred µm), where MPB cells accumulate during diurnal low tides. This work provides the first direct experimental evidence of DIC limitation of photosynthesis in highly productive intertidal MPB communities.
authors.affiliation: Marine and Environmental Sciences Centre (MARE), Faculdade de Ciências da Universidade de Lisboa, 1749-016, Lisbon, Portugal.|Biosystems and Integrative Sciences Institute (BioISI), Universidade de Lisboa, Campo Grande, 1749-016, Lisbon, Portugal.|Departamento de Biologia Vegetal, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016, Lisbon, Portugal.
authors.forename: Sónia
authors.initials: S
authors.lastname: Vieira
authors.affiliation: Marine Biological Section, Department of Biology, University of Copenhagen, Strandpromenaden 5, 3000, Helsingør, Denmark.
authors.forename: Paulo
authors.initials: P
authors.lastname: Cartaxana
authors.affiliation: Departamento de Biologia Vegetal, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016, Lisbon, Portugal.|Centre for Ecology, Evolution and Environmental Changes (Ce3C), Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016, Lisbon, Portugal.
authors.forename: Cristina
authors.initials: C
authors.lastname: Máguas
authors.affiliation: Biosystems and Integrative Sciences Institute (BioISI), Universidade de Lisboa, Campo Grande, 1749-016, Lisbon, Portugal. jmlsilva@fc.ul.pt.|Departamento de Biologia Vegetal, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016, Lisbon, Portugal. jmlsilva@fc.ul.pt.
authors.forename: Jorge
authors.identifier: http://orcid.org/0000-0002-5583-2715
authors.initials: J
authors.lastname: Marques da Silva
mesh_terms: D001682:Biological Availability; D002244:Carbon / Q000378:metabolism / Q000493:pharmacokinetics*; D002245:Carbon Dioxide / Q000378:metabolism; D002247:Carbon Isotopes / Q000032:analysis; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D017377:Diatoms / Q000502:physiology*; D017753:Ecosystem; D004579:Electron Transport; D063366:Estuaries; D010788:Photosynthesis; D011174:Portugal
chemical_list: D002247:Carbon Isotopes; D002734:Chlorophyll; D002245:Carbon Dioxide; D002244:Carbon; D000077194:Chlorophyll A
keywords: Chlorophyll fluorescence; Dissolved inorganic carbon; Isotope discrimination; Microphytobenthos; Phaeodactylum tricornutum; Photosynthesis