Carbon Sequestration in the Form of Recalcitrant Dissolved Organic Carbon in a Seaweed (Kelp) Farming Environment

Abstract

Under climate change scenarios, the contribution of macroalgae to carbon sequestration has attracted wide attention. As primary producers, macroalgae can release substantial amounts of dissolved organic carbon (DOC) in seawater. However, little is known about the molecular composition and chemical properties of DOC derived from macroalgae and which of them are recalcitrant DOC (RDOC) that can be sequestered for a long time in the ocean. In the most intensive seaweed (kelp) farming area (Sanggou Bay) in China, we found that kelp mariculture not only significantly increased DOC concentration, but also introduced a variety of new DOC molecular species, many of which were sulfur-containing molecules. A long-term DOC degradation experiment revealed that those DOC with strong resistance to microbial degradation, i.e., RDOC, account for approximately 58% of the DOC extracted from kelp mariculture area. About 85% (3587 out of 4224 with different chemical features) of the RDOC molecular species were steadily present throughout the long-term degradation process. 15% (637 out of 4224 with different chemical features) of the RDOC molecular species were likely newly generated by microorganisms after metabolizing macroalgae-derived labile DOC. All these stable RDOC should be included in the blue carbon budgets of seaweed.

Kelp Culture Enhances Coastal Biogeochemical Cycles by Maintaining Bacterioplankton Richness and Regulating Its Interactions

“…However, most related investigations have only considered the direct absorption of these substances by the seaweed itself ( 44 – 46 ). Admittedly, direct absorption by seaweed is the dominant element fixation pathway; however, the microbes related to seaweed cultivation in biogeochemical cycles also contribute substantially ( 47 ). Our study results revealed that seaweed culture activities effectively promoted the biogeochemical cycles of bacterioplankton in the culture areas.…”

Effect of hyposaline stress on the release of dissolved organic carbon from five common macroalgal species

“…Macroalgae can release a large amount of DOC to the environment during growth, and this makes macroalgae have a high carbon sink potential (Krause-Jensen and Duarte, 2016; Ortega et al, 2019;Watanabe et al, 2020;Li et al, 2022). However, a variety of environmental stressors have significant effects on DOC release from macroalgae (Paine et al, 2021;Hurd et al, 2022).…”

Green Tides Significantly Alter the Molecular Composition and Properties of Coastal DOC and Perform Dissolved Carbon Sequestration

“…prolifera than in those without this macroalgae (Figure S6). As macroalgae are rich in sulfur-containing substances (e.g., sulfated polysaccharides), − the much higher proportion of CHOS in the newly introduced DOC molecules suggests that these were derived mainly from U. prolifera as this was the dominant macroalgal species in our sampling area.…”