Impacts of Spartina alterniflora invasion on coastal carbon cycling within a native Phragmites australis-dominated wetland

Abstract

Despite its significance for climate adaptation, the impact of non-native Spartina alterniflora on coastal blue carbon cycling remains unclear. While it is generally reported that S. alterniflora invasion increases the soil organic carbon (SOC) stock along China's coastlines from tropical to subtropical climate zones, some cases, such as the Jiuduansha wetland in the Yangtze River estuary, show a different pattern. To clarify the impacts of S. alterniflora invasion on carbon cycling within a native Phragmites australis-dominated wetland, a comprehensive study was conducted in the Yangtze River estuary, employing a multidisciplinary approach that integrated eddy covariance (EC) measurements, soil and water sampling, and satellite remote sensing. The EC measurements revealed that three marshes (S. alterniflora saltmarsh, native Phragmites australis saltmarsh, and P. australis freshwater marsh) functioned as net carbon sinks annually, with S. alterniflora saltmarsh capturing 822.57 g C m⁻² yr⁻¹, which was 86.13 % and 54.27 % higher than P. australis saltmarsh (NEE=−441.93 g C m⁻² yr⁻¹) and P. australis freshwater marsh (NEE=−533.21 g C m⁻² yr⁻¹), respectively. This suggests that enhanced lateral carbon fluxes from the wetland to the estuary underlie the higher primary production but lower SOC storage observed in S. alterniflora wetlands. This possibility is further supported by higher satellite-derived dissolved organic carbon concentrations in the tidal creeks adjacent to S. alterniflora compared to those near P. australis marshes, which were significantly correlated with satellite-derived non-photosynthetic vegetation fractional cover. This study underscores the role of non-native S. alterniflora in facilitating carbon transfer from the atmosphere to the estuary, in contrast to native P. australis, and highlights that effective S. alterniflora management is beneficial for the synergistic enhancement of wetland restoration, conservation, and carbon sequestration.