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<p>Macroalgae release dissolved organic carbon (DOC) into their surrounding seawater, with a portion classified as recalcitrant DOC (RDOC), which potentially contributes to long-term ocean carbon sequestration. However, the dynamic changes in RDOC contributions throughout the macroalgal growth cycle remain poorly understood, limiting comprehensive assessments of RDOC-based carbon sequestration by macroalgae. Here, we conducted mesocosm experiments at different kelp growth stages to investigate the dynamics of RDOC production in terms of both quality and quantity. Our results revealed significant variations in DOC release across different kelp growth stages, with a notable increase in both the proportion and absolute quantity of RDOC. From the sporeling stage to maturity, the RDOC fraction in released DOC increased from 24% to 48%, while the RDOC contribution rate per kelp individual rose from 0.2 mg C d<sup>−1</sup> to 478 mg C d<sup>−1</sup>, indicating an increasing dominance of RDOC in macroalgal environments as kelp grows. Additionally, using a dynamic growth model tailored to local farming conditions and definite integration, we estimated the total RDOC contribution over the full kelp growth cycle. A single kelp individual, with a wet weight gain of 2.0 kg, contributed approximately 52.7 g C in RDOC—nearly equivalent to the biomass carbon of harvested kelp (60 g C). Collectively, these findings highlight the significant role of seaweed farming in ocean carbon sequestration over the entire cultivation period. Therefore, RDOC-mediated carbon sequestration in seaweed farming should not be overlooked in evaluations of its contribution to global carbon cycles.</p>

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Neglecting recalcitrant DOC would lead to serious underestimation of seaweed farming’s contribution to ocean carbon sequestration

  • 期刊论文

  • 发表日期：

    2025年4月14日

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  • Xiuting Feng,
  • Hongmei Li,
  • Jihong Zhang,
  • Kunxian Tang,
  • Longfei Lu,
  • Lirong Chang,
  • Yongyu Zhang

摘要

Macroalgae release dissolved organic carbon (DOC) into their surrounding seawater, with a portion classified as recalcitrant DOC (RDOC), which potentially contributes to long-term ocean carbon sequestration. However, the dynamic changes in RDOC contributions throughout the macroalgal growth cycle remain poorly understood, limiting comprehensive assessments of RDOC-based carbon sequestration by macroalgae. Here, we conducted mesocosm experiments at different kelp growth stages to investigate the dynamics of RDOC production in terms of both quality and quantity. Our results revealed significant variations in DOC release across different kelp growth stages, with a notable increase in both the proportion and absolute quantity of RDOC. From the sporeling stage to maturity, the RDOC fraction in released DOC increased from 24% to 48%, while the RDOC contribution rate per kelp individual rose from 0.2 mg C d−1 to 478 mg C d−1, indicating an increasing dominance of RDOC in macroalgal environments as kelp grows. Additionally, using a dynamic growth model tailored to local farming conditions and definite integration, we estimated the total RDOC contribution over the full kelp growth cycle. A single kelp individual, with a wet weight gain of 2.0 kg, contributed approximately 52.7 g C in RDOC—nearly equivalent to the biomass carbon of harvested kelp (60 g C). Collectively, these findings highlight the significant role of seaweed farming in ocean carbon sequestration over the entire cultivation period. Therefore, RDOC-mediated carbon sequestration in seaweed farming should not be overlooked in evaluations of its contribution to global carbon cycles.