Changes in Soil Organic Carbon Dynamics in a Native C4Plant-Dominated Tidal Marsh Following Spartina alternifloraInvasion

Invasion of an exotic C4plant Spartina alterniflorahas been shown to increase soil organic carbon (SOC) concentrations in native C3plant-dominated coastal wetlands of China. However, little is known about the effects of S. alterniflorainvasion on SOC concentrations and fractions in tidal marshes dominated by native C4plants. In this study, a field experiment was conducted in a tidal marsh dominated by the native C4plant Cyperus malaccensisin 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. malaccensiscommunity, as well as those of three S. alternifloracommunities 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. malaccensiscommunity increased with the duration of S. alterniflorainvasion, whereas SOC concentrations in the 10–50-cm soils decreased slightly during the initial period of S. alterniflorainvasion, 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. alterniflorainvasion. The findings of this study suggest that invasion of the exotic C4plant S. alterniflorainto a marsh dominated by the native C4plant C. malaccensiswould enhance SOC sequestration owing to the greater amount of biomass and lower proportion of labile SOC fractions present in the S. alternifloracommunities.