Warming enhances carbon dioxide and methane fluxes from Red Sea seagrass ( Halophila stipulacea) sediments

Burkholz, Celina; Garcias-Bonet, Neus; Duarte, Carlos M.

Seagrass meadows are autotrophic ecosystems acting as carbon sinks, but they have also been shown to be sources of carbon dioxide (inline-formulaCO2) and methane (inline-formulaCH4). Seagrasses can be negatively affected by increasing seawater temperatures, but the effects of warming on inline-formulaCO2 and inline-formulaCH4 fluxes in seagrass meadows have not yet been reported. Here, we examine the effect of two disturbances on air–seawater fluxes of inline-formulaCO2 and inline-formulaCH4 in Red Sea Halophila stipulacea communities compared to adjacent unvegetated sediments using cavity ring-down spectroscopy. We first characterized inline-formulaCO2 and inline-formulaCH4 fluxes in vegetated and adjacent unvegetated sediments, and then experimentally examined their response, along with that of the carbon (C) isotopic signature of inline-formulaCO2 and inline-formulaCH4, to gradual warming from 25 inline-formulaC (winter seawater temperature) to 37 inline-formulaC, 2 inline-formulaC above current maximum temperature. In addition, we assessed the response to prolonged darkness, thereby providing insights into the possible role of suppressing plant photosynthesis in supporting inline-formulaCO2 and inline-formulaCH4 fluxes. We detected 6-fold-higher inline-formulaCO2 fluxes in vegetated compared to bare sediments, as well as 10- to 100-fold-higher inline-formulaCH4 fluxes. Warming led to an increase in net inline-formulaCO2 and inline-formulaCH4 fluxes, reaching average fluxes of 10 422.18 inline-formula± 2570.12 inline-formulaµmol inline-formulaCO2 minline-formula−2 dinline-formula−1 and inline-formula88.11±15.19inline-formulaµmol inline-formulaCH4 minline-formula−2 dinline-formula−1, while inline-formulaCO2 and inline-formulaCH4 fluxes decreased over time in sediments maintained at 25 inline-formulaC. Prolonged darkness led to an increase in inline-formulaCO2 fluxes but a decrease in inline-formulaCH4 fluxes in vegetated sediments. These results add to previous research identifying Red Sea seagrass meadows as a significant source of inline-formulaCH4, while also indicating that sublethal warming may lead to increased emissions of greenhouse gases from seagrass meadows, providing a feedback mechanism that may contribute to further enhancing global warming.

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Burkholz, Celina / Garcias-Bonet, Neus / Duarte, Carlos M.: Warming enhances carbon dioxide and methane fluxes from Red Sea seagrass (Halophila stipulacea) sediments. 2020. Copernicus Publications.

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