MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps14657

ABSTRACT: The seed sheaths of eelgrass (Zostera marina L.) have recently been shown to possess photosynthetic capacity that can alleviate intra-seed hypoxic conditions and thereby enhance biosynthetic activity. However, nothing is known about how increasing seawater temperatures affect physiological responses in developing Z. marina seeds. We used an optical multi-analyte sensor system in combination with O₂-sensitive sensor spots to measure rates of photosynthesis and dark respiration within custom-made gas exchange chambers. Exponential saturation models were then applied to determine key photosynthetic parameters, such as maximum photosynthesis rates (P_MAX), light use efficiencies (α), saturating photon irradiances (E_K), compensation photon irradiances (E_C), and net diel O₂ budgets. Our results showed that both photosynthetic activity and dark respiration rates in sheath-covered seeds increased with increasing seawater temperature (from 10 to 25 °C), but with a 2-fold stronger response in dark respiration as compared to gross photosynthesis over the measured temperature range. These temperature responses resulted in increasing light requirements (from 47 to 183 µmol photons m^-2 s^-1 in E_K) and decreasing net diel O₂ budgets (from -5.4 to -126 nmol O₂ mg WW^-1 h^-1) of the eelgrass seeds with increasing temperature. Eelgrass seed exposure to high temperature led thus to highly reduced net diel O₂ balances, which is expected to have detrimental effects on seed development and germination success owing to negative effects on synthesis rates of storage products in the endosperm.