Internal leaf and meristem O2 and H2S dynamics of a tropical seagrass identify mechanisms of large-scale die-off events

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Christopher R Johnson, Marguerite Koch, C McNicholl, Ole Pedersen, C. J. Madden

While cosmopolitan seagrasses are ecologically important, large-scale (>50 km2) mortality events are becoming more frequent globally, driven by coastal eutrophication and global change that promote hypoxia and sediment H2S accumulation. To identify mechanisms causing internal plant hypoxia and H2S intrusion, we conducted a series of laboratory and field studies, placing microsensors into the leaf (O2) and meristematic shoot (O2 and H2S) tissue lacunae of the dominant subtropical-Atlantic-Caribbean seagrass, Thalassia testudinum. At a site with recurrent die-off events in Florida Bay, gas dynamics were measured monthly with several consistent patterns emerging. There was a strong linear relationship (R2=0.99) between leaf/meristem pO2 and irradiance with leaves and meristems reaching 60 and 35 kPa O2 within a few hours of sunrise. When the meristem O2 level was only 4.5 kPa at sunset, lower than any other run, the meristem became anoxic within 1-2 hrs and H2S intruded into the meristem within 3 hrs. Laboratory experiments examining hypersalinity and water column hypoxia stress, support the importance of high meristem pO2 at the onset of darkness to prevent H2S intrusion. The inability of T. testudinum leaves to pressurize lacunae above water column pO2 saturation (>21 kPa) under hypersalinity (65 psu) in the light resulted in a low initial meristem pO2 at darkness that caused H2S intrusion, similar to conditions in the field at ambient salinity. Thus, maintaining a high pO2 in the meristem lacunae in the light before sunset is likely critical to avoid H2S intrusion at night and a potential seagrass die-off event.
Original languageEnglish
Publication date16 Feb 2020
Publication statusPublished - 16 Feb 2020
EventOcean Sciences Meeting 2020 - San Diego, United States
Duration: 16 Feb 202021 Feb 2020
https://www.agu.org/ocean-sciences-meeting

Conference

ConferenceOcean Sciences Meeting 2020
LocationSan Diego
CountryUnited States
Period16/02/202021/02/2020
Internet address

ID: 227182492