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Authors Johnson, CR; Koch, MS; Pedersen, O; Madden, CJ
Author Full Name Johnson, C. R.; Koch, M. S.; Pedersen, O.; Madden, C. J.
Title Hypersalinity affects leaf and meristem O-2 dynamics exposing meristems to H2S in the dominant tropical seagrass Thalassia testudinum
Source JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY
Language English
Document Type Article
Author Keywords Hypoxia; Microsensor; Florida Bay; Seagrasses; Die-off; Mortality
Keywords Plus DIE-OFF EVENTS; FLORIDA BAY; OXYGEN DYNAMICS; ZOSTERA-MARINA; SULFIDE; SEDIMENT; SUBMERGENCE; RHIZOSPHERE; TOLERANCE; INTRUSION
Abstract Large-scale (> 80 km(2)) seagrass mortality events have been reported worldwide. While the mechanisms triggering these sudden die-off events are not well understood, plant hypoxia and H2S intrusion, at times linked to hypersaline conditions, have been suggested to play a role. In the present study, we used microsensors (similar to 100 mu m) to measure pO(2) light-dark dynamics (4 and 1 h, light:dark) in the leaf, and simultaneously pO(2) and H2S in the meristem, of the tropical seagrass, Thalassia testudinum. The role of leaf pO(2) in mitigating H2S intrusion into the meristem was examined. We also assessed the interactive effect of water column hypoxia and hypersalinity (35, 45, 55, 65) on meristem pO(2) light-dark dynamics and H2S intrusion. Internal gas dynamics were measured from seagrass shoots in intact cores collected at a site with recurrent die-off events in Florida Bay, USA. When the overlying water column pO(2) was maintained at air equilibrium (20 kPa), the leaf pO(2) in shoots at <= 55 salinity was supersaturated (30 to 35 kPa) with respect to the water column. However, leaves of shoots at 65 salinity in the light maintained leaf pO(2) on par with the water column (similar to 20-25 kPa), even after 4 h. This was the case even though the initial (10 min) leaf Delta pO(2) was similar across salinity treatments, suggesting 65 salinity limited O-2 pressurization, rather than, or in addition to, O-2 production. The low leaf pO(2) at 65 salinity in the light limited meristem pO(2) (similar to 10 kPa pO(2)) at the start of the dark cycle. Consequently, the meristem pO(2) threshold of similar to 1.5 kPa pO(2) was reached within 1-2 h of the dark cycle, and H2S intrusion occurred. Further, at 65 salinity, H2S intrusion occurred at higher water column pO(2) (10-15 kPa), compared to salinity <= 55 (similar to 5 kPa). Meristem minimum pO(2) were also lower in the dark at higher salinity, indicating a greater belowground O-2 demand. Based on these experimental microsensor results, we suggest two primary goals to minimize hypoxia and H2S-induced seagrass mortality: (1) minimize hypersaline conditions to increase the efficiency of seagrass leaf and meristem O-2 pressurization, and (2) reduce nutrient loads and hypersaline conditions to keep water column pO(2) at a maximum and lower sediment-meristem O-2 demand in the dark.
Author Address [Johnson, C. R.; Koch, M. S.] Florida Atlantic Univ, Biol Sci Dept, Aquat Plant Ecol Lab, 777 Glades Rd, Boca Raton, FL 33431 USA; [Pedersen, O.] Univ Copenhagen, Dept Biol, Univ Pk 4,3rd Floor, DK-2100 Copenhagen, Denmark; [Madden, C. J.] South Florida Water Management Dist, Everglades Ecosyst Res Div, W Palm Beach, FL 33406 USA
Reprint Address Koch, MS (corresponding author), Florida Atlantic Univ, Biol Sci Dept, Aquat Plant Ecol Lab, 777 Glades Rd, Boca Raton, FL 33431 USA.
E-mail Address mkoch@fau.edu
ResearcherID Number Johnson, Christopher/AAE-2840-2021; Pedersen, Ole/F-2476-2011
ORCID Number Pedersen, Ole/0000-0002-0827-946X
Funding Agency and Grant Number South Florida Water Management District (West Palm Beach, FL)
Funding Text We acknowledge the South Florida Water Management District (West Palm Beach, FL) for funding this research and Everglades National Park (Homestead, FL) for their logistical support through the Flamingo Marina. We thank our colleague Dr. McNicholl for his assistance in the field and lab. We also appreciate the time and effort of two anonymous reviewers and editors.
Publisher ELSEVIER
Publisher City AMSTERDAM
Publisher Address RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS
ISSN 0022-0981
29-Character Source Abbreviation J EXP MAR BIOL ECOL
ISO Source Abbreviation J. Exp. Mar. Biol. Ecol.
Publication Date DEC
Year Published 2020
Volume 533
Article Number 151458
Digital Object Identifier (DOI) 10.1016/j.jembe.2020.151458
Page Count 10
Web of Science Category Ecology; Marine & Freshwater Biology
Subject Category Environmental Sciences & Ecology; Marine & Freshwater Biology
Document Delivery Number OP7SI
Unique Article Identifier WOS:000588286500004
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