Purpose

We investigated S. alterniflora saltmarshes in 10 regions to distinguish the major sources of soil organic carbon (SOC) and provide data for SOC content in Chinese coastal wetlands under exotic invasion.

Methods

We collected soil and plant samples. We analyzed the soil properties for SOC content, recalcitrant organic carbon (RC), labile organic carbon (LC), total nitrogen (TN), total phosphorus (TP), total salinity and water content, as well as stable isotopic carbon composition (δ¹³C) in the SOC and RC. SOC and RC were determined using a Shimadzu TOC analyzer. We used δ¹³C values and C/N ratios of the SOC to identify carbon source inputs. The δ¹³C of the SOC and RC was measured using a Sercon Integra CN isotope ratio mass spectrometer.

Results

The results showed that the S. alterniflora saltmarsh SOC pool properties differed significantly between study areas, dependent upon local circumstances and carbon exchanges. The δ¹³C values of SOC in surface sediments from Tianjin to Guangxi were from −25.16 to −20.64‰, RC from −27.82 to −23.1‰, and C/N ratios between 11.36 and 19.00. These samples had SOC values of 14.77–23.95 g kg⁻¹, RC values of 11.98–21.44 g kg⁻¹, and LC values of 0.44–4.08 g kg⁻¹. The SOC and RC of surface sediments were positively correlated with TN and TP.

Conclusions

S. alterniflora saltmarsh SOC is derived from multiple carbon inputs including from marine and land sources and its formation is driven by complicated factors. TN and TP inputs increase SOC in coastal wetlands. Generally, terrigenous carbon inputs dominate the SOC composition in Chinese coastal wetlands, although marine-derived organic carbon (OC) inputs to sediment increase from northern to southern areas.