Radiocarbon isotopic evidence for assimilation of atmospheric CO₂ by the seagrass <i>Zostera marina</i>

• Main Authors: K. Watanabe, T. Kuwae
• Format: Article
• Language: English
• Published: Copernicus Publications 2015-10-01
• Series: Biogeosciences
• Online Access: http://www.biogeosciences.net/12/6251/2015/bg-12-6251-2015.pdf

Submerged aquatic vegetation takes up water-column dissolved inorganic carbon (DIC) as a carbon source across its thin cuticle layer. It is expected that marine macrophytes also use atmospheric CO₂ when exposed to air during low tide, although assimilation of atmospheric CO₂ has never been quantitatively evaluated. Using the radiocarbon isotopic signatures (Δ¹⁴C) of the seagrass <i>Zostera marina</i>, DIC and particulate organic carbon (POC), we show quantitatively that <i>Z. marina</i> takes up and assimilates atmospheric modern CO₂ in a shallow coastal ecosystem. The Δ¹⁴C values of the seagrass (−40 to −10 &permil;) were significantly higher than those of aquatic DIC (−46 to −18 &permil;), indicating that the seagrass uses a ¹⁴C-rich carbon source (atmospheric CO₂, +17 &permil;). A carbon-source mixing model indicated that the seagrass assimilated 0–40 % (mean, 17 %) of its inorganic carbon as atmospheric CO₂. CO₂ exchange between the air and the seagrass might be enhanced by the presence of a very thin film of water over the air-exposed leaves during low tide. Our radiocarbon isotope analysis, showing assimilation of atmospheric modern CO₂ as an inorganic carbon source, improves our understanding of the role of seagrass meadows in coastal carbon dynamics.