The effect of biomass variations of Spartina alterniflora on the organic carbon content and composition of a salt marsh in northern Jiangsu Province, China

The relationship of the organic carbon content and surface sediment composition to the litter mass of Spartina alterniflora was analyzed to investigate the responses of organic carbon content and composition to biomass changes in a salt marsh after the introduction of S. alterniflora. The vertical distribution of sediment organic carbon and its relationship with S. alterniflora underground biomass was also examined. The results show that the total organic carbon (TOC), recalcitrant carbon (RC) and labile carbon (LC) contents were significantly greater in the surface sediments of the S. alterniflora flat, which showed different intra-annual variation trends compared to a bare flat. In particular, the majority of S. alterniflora-derived organic carbon was LC in the S. alterniflora flat sediments, indicating that the introduction of S. alterniflora resulted in a significant increase in surface sediment LC content. In addition, the results of S. alterniflora litter decomposition revealed a rapid decrease of 40% in the organic carbon stocks within the first 2 months, and the TOC and LC contents showed intra-annual variation trends similar to the surface litter mass but with a two-month “phase difference” in time. Further analysis indicated, S. alterniflora litter controlled the content and proportion of the S. alterniflora-derived TOC input, and it ultimately affected the TOC content variations in the sediments. However, due to the LC mainly originated from S. alterniflora, the surface litter exerted more significant impact on the variation of LC content. In the bare flat core, the relatively low TOC, RC and LC content values were significantly influenced by the grain control effect, and the origins of these components were mainly derived from non-S. alterniflora sources. However, in the S. alterniflora flat cores, the relationships between organic carbon content, grain size and underground biomass, together with the analysis of the organic carbon origins, indicated that the S. alterniflora underground biomass significantly affected the origin of organic carbon. In addition, Spartina alterniflora introduction significantly increased the carbon sequestration capacity of the tidal salt marsh in North Jiangsu. Furthermore, the TOC, LC and RC accumulation rate analyses also indicated that S. alterniflora introduction improved the salt marsh soil and was beneficial to long-term carbon sequestration of the organic carbon pool.