Max Planck Institute for Marine Microbiology, 28359 Bremen, Germany.
University of Bremen, Center for Marine Environmental Sciences, MARUM, 28359 Bremen, Germany.
Proc Natl Acad Sci U S A. 2023 Jan 3;120(1):e2210561119. doi: 10.1073/pnas.2210561119. Epub 2022 Dec 30.
Brown algae annually convert gigatons of carbon dioxide into carbohydrates, including the complex extracellular matrix polysaccharide fucoidan. Due to its persistence in the environment, fucoidan is potentially a pathway for marine carbon sequestration. Rates of fucoidan secretion by brown algae remain unknown due to the challenge of identifying and quantifying complex polysaccharides in seawater. We adapted the techniques of anion exchange chromatography, enzyme-linked immunosorbent assay, and biocatalytic enzyme-based assay for detection and quantification of fucoidan. We found the brown alga at the Baltic Sea coast of south-west Finland to secrete 0.3% of their biomass as fucoidan per day. Dissolved fucoidan concentrations in seawater adjacent to algae reached up to 0.48 mg L. Fucoidan accumulated during incubations of , significantly more in light than in darkness. Maximum estimation by acid hydrolysis indicated fucoidan secretion at a rate of 28 to 40 mg C kg h, accounting for 44 to 50% of all exuded dissolved organic carbon. Composed only of carbon, oxygen, hydrogen, and sulfur, fucoidan secretion does not consume nutrients enabling carbon sequestration independent of algal growth. Extrapolated over a year, the algae sequester more carbon into secreted fucoidan than their biomass. The global utility of fucoidan secretion is an alternative pathway for carbon dioxide removal by brown algae without the need to harvest or bury algal biomass.
褐藻每年将数十亿吨二氧化碳转化为碳水化合物，包括复杂的细胞外基质多糖褐藻糖胶。由于褐藻糖胶在环境中持久存在，因此它有可能成为海洋碳封存的途径。由于难以识别和量化海水中的复杂多糖，褐藻分泌褐藻糖胶的速率仍不清楚。我们采用阴离子交换色谱、酶联免疫吸附测定和基于生物催化酶的测定技术来检测和定量褐藻糖胶。我们发现，芬兰西南部波罗的海沿岸的褐藻每天分泌其生物量的 0.3%作为褐藻糖胶。与藻类相邻的海水中溶解的褐藻糖胶浓度高达 0.48 毫克/升。在对 的孵育过程中，褐藻糖胶积累，光照下的积累量明显多于黑暗下的积累量。酸水解的最大估计值表明，褐藻糖胶的分泌速率为 28 至 40 毫克 C kg h，占所有分泌溶解有机碳的 44%至 50%。褐藻糖胶仅由碳、氧、氢和硫组成，分泌褐藻糖胶不会消耗营养物质，从而使碳封存独立于藻类生长成为可能。根据推算，藻类通过分泌褐藻糖胶固定的碳量超过其生物量。褐藻分泌褐藻糖胶是去除二氧化碳的另一种途径，无需收获或掩埋藻类生物质，在全球范围内具有广泛的应用前景。
