Exotic Spartina alterniflora invasion alters ecosystem-atmosphere exchange of CH4 and N2O and carbon sequestration in a coastal salt marsh in China.

Coastal salt marshes are sensitive to global climate change and may play an important role in mitigating global warming. To evaluate the impacts of Spartina alterniflora invasion on global warming potential ( GWP) in Chinese coastal areas, we measured CH₄ and N₂O fluxes and soil organic carbon sequestration rates along a transect of coastal wetlands in Jiangsu province, China, including open water; bare tidal flat; and invasive S. alterniflora, native Suaeda salsa, and Phragmites australis marshes. Annual CH₄ emissions were estimated as 2.81, 4.16, 4.88, 10.79, and 16.98 kg CH₄ ha⁻¹ for open water, bare tidal flat, and P. australis, S. salsa, and S. alterniflora marshes, respectively, indicating that S. alterniflora invasion increased CH₄ emissions by 57-505%. In contrast, negative N₂O fluxes were found to be significantly and negatively correlated ( P < 0.001) with net ecosystem CO₂ exchange during the growing season in S. alterniflora and P. australis marshes. Annual N₂O emissions were 0.24, 0.38, and 0.56 kg N₂O ha⁻¹ in open water, bare tidal flat and S. salsa marsh, respectively, compared with -0.51 kg N₂O ha⁻¹ for S. alterniflora marsh and −0.25 kg N₂O ha⁻¹ for P. australis marsh. The carbon sequestration rate of S. alterniflora marsh amounted to 3.16 Mg C ha⁻¹ yr⁻¹ in the top 100 cm soil profile, a value that was 2.63- to 8.78-fold higher than in native plant marshes. The estimated GWP was 1.78, −0.60, −4.09, and −1.14 Mg CO₂eq ha⁻¹ yr⁻¹ in open water, bare tidal flat, P. australis marsh and S. salsa marsh, respectively, but dropped to −11.30 Mg CO₂eq ha⁻¹ yr⁻¹ in S. alterniflora marsh. Our results indicate that although S. alterniflora invasion stimulates CH₄ emissions, it can efficiently mitigate increases in atmospheric CO₂ and N₂O along the coast of China. [ABSTRACT FROM AUTHOR]