The impact of sea embankment reclamation on soil organic carbon and nitrogen pools in invasive Spartina alterniflora and native Suaeda salsa salt marshes in eastern China

Abstract

The construction of sea embankments is an increasingly common approach for controlling the spread of the exotic C4 perennial grass Spartina alterniflora Loisel. in coastal wetlands of eastern China. However, the impact of sea embankment reclamation on the soil organic carbon (C) and nitrogen (N) dynamics in salt marshes is not fully understood. In this study, we examined the stocks of the total, labile and recalcitrant organic C and N, the recalcitrant indices of C and N, and the concentrations of water-soluble organic carbon (WSOC), microbial biomass carbon (MBC) and cumulative CO2-C mineralization (MINC) in sea embankment-reclaimed S. alterniflora and Suaeda salsa (Linn.) Pall. salt marshes through comparisons with adjacent unreclaimed S. alterniflora and S. salsa salt marshes in a coastal wetland of eastern China. Sea embankment reclamation significantly decreased plant biomass by 55.34%, soil salinity by 81.71%, soil moisture by 43.16%, soil total organic C by 50.60% and total organic N by 49.99%, and also lowered labile and recalcitrant organic C and N, WSOC, MBC and MINC in the invasive S. alterniflora salt marsh. However, sea embankment reclamation did not significantly affect the stocks of the soil organic total C and N, recalcitrant organic C and N, and soil organic C dynamics in the native S. salsa salt marsh, possibly because the total quantity of S. salsa materials entering the soil, soil salinity, moisture and bulk density were not affected by sea embankment reclamation. Our results suggest that the impact of sea embankment reclamation on soil organic C and N pools is much more profound in S. alterniflora salt marsh than in S. salsa salt marsh. Sea embankment reclamation could greatly weaken the C and N sinks of S. alterniflora salt marsh and potentially affect C and N sinks in the coastal wetlands of eastern China.