TY - JOUR

T1 - Irradiance, Water Column O2, and Tide Drive Internal O2 Dynamics and Meristem H2S Detection in the Dominant Caribbean-Tropical Atlantic Seagrass, Thalassia testudinum

AU - Koch, M. S.

AU - Johnson, C. R.

AU - Madden, C. J.

AU - Pedersen, O.

N1 - Publisher Copyright: © 2022, Coastal and Estuarine Research Federation.

PY - 2022

Y1 - 2022

N2 - Water column hypoxia, low partial pressure of oxygen (pO2), and hydrogen sulfide (H2S) intrusion, a phytotoxin, are factors linked to global seagrass decline. While many lab experiments have examined these relationships, field studies are needed to elucidate complex drivers of internal pO2 in situ. Herein, we examined plant pO2 and H2S dynamics using microsensors in a dominant tropical seagrass Thalassia testudinum in Florida Bay, a subtropical estuary with recurrent seagrass die-off events. Based on 12 field deployments (48–72 h) across seasons, we show that T. testudinum has a high capacity for daytime leaf oxidation (42–53 kPa) that sustains oxic conditions in its tissues and supersaturates the water column with O2 (> 21 kPa). Although internal daytime O2 is rapidly consumed near sunset, daytime seagrass O2 production leads to supersaturation in the water column beyond sunset. This is an important feedback mechanism as high water column pO2 at night buffers against internal leaf hypoxia via diffusion. Even with high daytime irradiance, however, shoot meristems went anoxic/hypoxic (0.6 kPa) at night, indicating high plant and ecosystem O2 consumption. Hydrogen sulfide was only detected in the meristem when water column pO2 was close to anoxia (< 1 kPa) coincident with maximum water column temperatures (33 °C), an occurrence likely to increase with global warming. Our results support the hypothesis that meristem H2S intrusion in Florida Bay, and likely globally, is primarily driven by insufficient internal plant oxidation by the water column at night, even when high irradiance sustains supersaturation of tissue O2 during the day.

AB - Water column hypoxia, low partial pressure of oxygen (pO2), and hydrogen sulfide (H2S) intrusion, a phytotoxin, are factors linked to global seagrass decline. While many lab experiments have examined these relationships, field studies are needed to elucidate complex drivers of internal pO2 in situ. Herein, we examined plant pO2 and H2S dynamics using microsensors in a dominant tropical seagrass Thalassia testudinum in Florida Bay, a subtropical estuary with recurrent seagrass die-off events. Based on 12 field deployments (48–72 h) across seasons, we show that T. testudinum has a high capacity for daytime leaf oxidation (42–53 kPa) that sustains oxic conditions in its tissues and supersaturates the water column with O2 (> 21 kPa). Although internal daytime O2 is rapidly consumed near sunset, daytime seagrass O2 production leads to supersaturation in the water column beyond sunset. This is an important feedback mechanism as high water column pO2 at night buffers against internal leaf hypoxia via diffusion. Even with high daytime irradiance, however, shoot meristems went anoxic/hypoxic (0.6 kPa) at night, indicating high plant and ecosystem O2 consumption. Hydrogen sulfide was only detected in the meristem when water column pO2 was close to anoxia (< 1 kPa) coincident with maximum water column temperatures (33 °C), an occurrence likely to increase with global warming. Our results support the hypothesis that meristem H2S intrusion in Florida Bay, and likely globally, is primarily driven by insufficient internal plant oxidation by the water column at night, even when high irradiance sustains supersaturation of tissue O2 during the day.

KW - Florida Bay

KW - Hypoxia

KW - Microsensor

KW - Seagrass

KW - Sulfide

KW - Thalassia testudinum

U2 - 10.1007/s12237-022-01064-y

DO - 10.1007/s12237-022-01064-y

M3 - Journal article

AN - SCOPUS:85128289878

VL - 45

SP - 2543

EP - 2559

JO - Estuaries and Coasts

JF - Estuaries and Coasts

SN - 1559-2723

IS - 8

ER -