Changes in Soil Organic Carbon Dynamics in a Native C4 Plant-Dominated Tidal Marsh Following Spartina alterniflora Invasion

Invasion of an exotic C-4 plant Spartina alterniflora has been shown to increase soil organic carbon (SOC) concentrations in native C-3 plant-dominated coastal wetlands of China. However, little is known about the effects of S. alterniflora invasion on SOC concentrations and fractions in tidal marshes dominated by native C-4 plants. In this study, a field experiment was conducted in a tidal marsh dominated by the native C-4 plant Cyperus malaccensis in the Minjiang River estuary, China. Concentrations of SOC and liable SOC fractions, dissolved organic carbon (DOC), microbial biomass carbon (MBC), and easily oxidizable carbon (EOC), were measured in the top 50-cm soils of the C. malaccensis community, as well as those of three S. alterniflora communities with an invasion duration of 0-4 years (SA-4), 4-8 years (SA-8), and 8-12 years (SA-12), respectively. Results showed that both SOC stocks in the 50-cm soils and mean SOC concentrations in the surface soils (0-10 cm) of the C. malaccensis community increased with the duration of S. alterniflora invasion, whereas SOC concentrations in the 10-50-cm soils decreased slightly during the initial period of S. alterniflora invasion, before increasing again. The pattern of changes in labile SOC fractions (DOC, MBC, and EOC) with invasion duration was generally similar to that of SOC, while the ratios of labile SOC fractions to total SOC (DOC:SOC, MBC:SOC, and EOC:SOC) decreased significantly with the duration of S. alterniflora invasion. The findings of this study suggest that invasion of the exotic C-4 plant S. alterniflora into a marsh dominated by the native C-4 plant C. malaccensis would enhance SOC sequestration owing to the greater amount of biomass and lower proportion of labile SOC fractions present in the S. alterniflora communities.