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

[摘要] Seagrass meadows are autotrophic ecosystems acting as carbon sinks, but they have also been shown to be sources of carbon dioxide ( CO 2 ) and methane ( CH 4 ). Seagrasses can be negatively affected by increasing seawater temperatures, but the effects of warming on CO 2 and CH 4 fluxes in seagrass meadows have not yet been reported. Here, we examine the effect of two disturbances on air–seawater fluxes of CO 2 and CH 4 in Red Sea Halophila stipulacea communities compared to adjacent unvegetated sediments using cavity ring-down spectroscopy. We first characterized CO 2 and CH 4 fluxes in vegetated and adjacent unvegetated sediments, and then experimentally examined their response, along with that of the carbon (C) isotopic signature of CO 2 and CH 4 , to gradual warming from 25  ∘ C (winter seawater temperature) to 37  ∘ C, 2  ∘ C 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 CO 2 and CH 4 fluxes. We detected 6-fold-higher CO 2 fluxes in vegetated compared to bare sediments, as well as 10- to 100-fold-higher CH 4 fluxes. Warming led to an increase in net CO 2 and CH 4 fluxes, reaching average fluxes of 10 422.18  ±  2570.12  µ mol  CO 2  m −2  d −1 and 88.11±15.19   µ mol  CH 4  m −2  d −1 , while CO 2 and CH 4 fluxes decreased over time in sediments maintained at 25  ∘ C. Prolonged darkness led to an increase in CO 2 fluxes but a decrease in CH 4 fluxes in vegetated sediments. These results add to previous research identifying Red Sea seagrass meadows as a significant source of CH 4 , 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.

[学科分类] 大气科学