TY - JOUR

T1 - Low irradiance disrupts the internal O2 dynamics of seagrass (Thalassia testudinum) leading to shoot meristem H2S intrusion

AU - Koch, M. S.

AU - Johnson, C. R.

AU - Madden, C. J.

AU - Pedersen, O.

PY - 2022

Y1 - 2022

N2 - Hypoxia and hydrogen sulfide (H2S) intrusion at night contribute to large-scale seagrass mortality events worldwide. Declining water quality has lowered irradiance and enhanced hypoxia in seagrass ecosystems, but linkages between low irradiance and seagrass internal pO2 in situ are not well understood. We examined low irradiance effects on leaf and meristem pO2 dynamics of a dominant tropical seagrass, Thalassia testudinum, using microsensors over multiple diurnal cycles. Further, we determined how O2 dynamics affect H2S intrusion into shoot meristems under low irradiance. Sequential days of low irradiance disrupted internal leaf O2 status in three ways: i) causing a longer lag in morning O2 pressurization, ii) depressing maximum pO2 during the day, and iii) shortening the time where maximum pO2 was sustained into the afternoon. There was a close relationship between leaf and water column pO2 during the day (R2 = 0.93 +/- 0.09); thus, internal O2 dynamics appear more dependent on water column pO2 under low irradiance. The nighttime minimum of leaf and meristem pO2 (1.2 and 0.4 kPa, respectively) were very low and the length of time the meristem sustained hypoxia (< 1.5 kPa pO2) at night was high (9:40 h:min). H2S intrusion into the meristem at night following 24-48 h of shading was persistent, likely the combined effect of limited internal O2 flow without saturating irradiances for photosynthesis, and a breakdown of the sediment oxic microshield. Under low irradiance, more frequent intrusions of H2S to the meristems increases the chances of large-scale seagrass mortality events at night.

AB - Hypoxia and hydrogen sulfide (H2S) intrusion at night contribute to large-scale seagrass mortality events worldwide. Declining water quality has lowered irradiance and enhanced hypoxia in seagrass ecosystems, but linkages between low irradiance and seagrass internal pO2 in situ are not well understood. We examined low irradiance effects on leaf and meristem pO2 dynamics of a dominant tropical seagrass, Thalassia testudinum, using microsensors over multiple diurnal cycles. Further, we determined how O2 dynamics affect H2S intrusion into shoot meristems under low irradiance. Sequential days of low irradiance disrupted internal leaf O2 status in three ways: i) causing a longer lag in morning O2 pressurization, ii) depressing maximum pO2 during the day, and iii) shortening the time where maximum pO2 was sustained into the afternoon. There was a close relationship between leaf and water column pO2 during the day (R2 = 0.93 +/- 0.09); thus, internal O2 dynamics appear more dependent on water column pO2 under low irradiance. The nighttime minimum of leaf and meristem pO2 (1.2 and 0.4 kPa, respectively) were very low and the length of time the meristem sustained hypoxia (< 1.5 kPa pO2) at night was high (9:40 h:min). H2S intrusion into the meristem at night following 24-48 h of shading was persistent, likely the combined effect of limited internal O2 flow without saturating irradiances for photosynthesis, and a breakdown of the sediment oxic microshield. Under low irradiance, more frequent intrusions of H2S to the meristems increases the chances of large-scale seagrass mortality events at night.

KW - Sulfide

KW - Shade

KW - Tide

KW - Florida Bay

KW - Microsensor

KW - Seagrass die-off

KW - Hypoxia

KW - DIE-OFF EVENTS

KW - TROPICAL SEAGRASS

KW - FLORIDA BAY

KW - OXYGEN DYNAMICS

KW - ZOSTERA-MARINA

KW - SULFIDE CONCENTRATIONS

KW - SEDIMENT SULFIDE

KW - LIGHT REDUCTION

KW - WATER-QUALITY

KW - GROWTH

U2 - 10.1016/j.aquabot.2022.103532

DO - 10.1016/j.aquabot.2022.103532

M3 - Journal article

VL - 181

JO - Aquatic Botany

JF - Aquatic Botany

SN - 0304-3770

M1 - 103532

ER -