Invasion of Spartina species enhance blue carbon functions by increasing CO₂ uptake and reducing methane emissions in Chinese and Danish coastal wetlands

The salt marsh ecosystem is vulnerable to disturbances like vegetation invasion, which alter community structure and ecosystem functions, particularly blue carbon sequestration. While previous studies have mainly focused on localized carbon storage post- Spartina invasion, there is a lack of comprehensive seasonal dynamics and multi-regional comparative analyses of carbon fluxes. This study evaluated the impacts of Spartina species invasion on carbon fluxes in salt marsh wetlands across China and Denmark. Both regions, sharing the same native plant species, Phragmites australis, yet differing in climatic conditions, offer ideal settings for exploring the broader effects on carbon cycle and climate feedback mechanisms. Monthly observations over an entire growing season revealed that Spartina invasions enhanced the carbon sequestration functions of coastal wetlands in both China and Denmark by increasing carbon dioxide (CO₂) sequestration and reducing methane (CH₄) emissions. CO₂ fluxes in Chinese coastal wetlands were about 10 times higher than those in Denmark, with minimal differences in CH₄ emissions. Furthermore, although CH₄ emission offset some of the CO₂ uptake, the overall radiative balance of Spartina remained lower than that of P. australis, suggesting that Spartina had the potential to mitigate global warming. Species-specific plant traits, like biomass, and abiotic factors, like air and soil temperature, affecting these fluxes in both countries’ salt marshes. This study highlighted the intricate interactions between invasive species and carbon dynamics, underscoring the importance of across-regional research to fully understand their role in global climate regulation.