17:15 〜 19:15
[ACG51-P03] 大型海藻・海草由来溶存有機炭素の分解性
キーワード：ブルーカーボン生態系、炭素動態、溶存有機炭素、藻場
As climate change intensifies, ocean-based solutions are increasingly recognized for their role in carbon sequestration. Coastal ecosystems, including macroalgae and seagrass beds, play a crucial role in carbon cycling by absorbing atmospheric CO2 and storing organic carbon (OC). While traditional blue carbon ecosystems (e.g., mangroves, salt marshes, and seagrass beds) have been well studied as sedimentary OC reservoirs, macroalgae also contribute significantly to the coastal carbon budget, primarily through the export of OC beyond their habitats. Among exported OC, dissolved organic carbon (DOC) derived from macroalgae and seagrass is considered a key pathway for long-term carbon storage. A fraction of this DOC resists degradation and persists as recalcitrant DOC (RDOC), which can remain in the ocean for over 100 years. However, RDOC formation and stability are not well understood due to variability in experimental conditions and the diverse traits of marine macrophytes. A systematic approach using standardized experimental protocols and predictive models, such as the reactivity continuum (RC) model, is needed to refine RDOC storage estimates. This study investigated DOC release and degradation dynamics in macroalgae and seagrass through field-bag experiments and degradation assays.
DOC release rates varied widely across macrophyte types (5–462 µmol g-DW-1 d-1). Macroalgae and seagrass showed comparable average DOC release rates of 100 and 137 µmol g-DW-1 d-1. Degradation experiments showed that RDOC fractions varied among macrophyte types. By Day 300, the RDOC fraction averaged 30.5% for macroalgae and 41.6% for seagrass. By Year 100, the RDOC fraction estimated using the RC model was 13.5% for macroalgae and 25.0% for seagrass, indicating the greater long-term stability of seagrass-derived DOC.
Fluorescence analysis identified four dissolved organic matter (DOM) components. Over 300-days degradation, fluorescence intensities (FIs) of humic-like components increased, while FIs of protein-like components decreased, suggesting selective preservation and microbial synthesis of humic-like compounds. RDOC fractions correlated positively with the ratio of humic-like FIs and DOC.
These findings enhance our understanding of macrophyte-derived DOC dynamics and its role in carbon sequestration, providing insights for blue carbon strategies and climate change mitigation.
DOC release rates varied widely across macrophyte types (5–462 µmol g-DW-1 d-1). Macroalgae and seagrass showed comparable average DOC release rates of 100 and 137 µmol g-DW-1 d-1. Degradation experiments showed that RDOC fractions varied among macrophyte types. By Day 300, the RDOC fraction averaged 30.5% for macroalgae and 41.6% for seagrass. By Year 100, the RDOC fraction estimated using the RC model was 13.5% for macroalgae and 25.0% for seagrass, indicating the greater long-term stability of seagrass-derived DOC.
Fluorescence analysis identified four dissolved organic matter (DOM) components. Over 300-days degradation, fluorescence intensities (FIs) of humic-like components increased, while FIs of protein-like components decreased, suggesting selective preservation and microbial synthesis of humic-like compounds. RDOC fractions correlated positively with the ratio of humic-like FIs and DOC.
These findings enhance our understanding of macrophyte-derived DOC dynamics and its role in carbon sequestration, providing insights for blue carbon strategies and climate change mitigation.