Variation of soil carbon and nitrogen storage in a natural restoration chronosequence of reclaimed temperate marshes

•SOC and TN storage increased with restoration time but fastest rates in first 8 years.•SOC and TN storage after 27 years of restoration was lower than in the natural marsh.•SOC and TN storage was affected by plant biomass and soil physicochemical properties. Wetland restoration significantly affects ecosystem carbon and nitrogen cycles by changing soil physicochemical properties and plant properties. To reveal the effect of wetland restoration on soil organic carbon (SOC) and total nitrogen (TN) storage, we measured the SOC and TN content and calculated their storage in a restoration chronosequence (1, 4, 8, 13, 17, 27 years) and compared them with those in a soybean field and a natural marsh, all in Sanjiang Plain, northeast China. Our results showed that the SOC and TN content and storage in the investigated sites increased with restoration time. However, the restoration rate was faster in the first 8 years but slowed down after 8 years of restoration. The SOC and TN content and storage decreased with soil depths in the eight sites. After 27 years of restoration, the carbon and nitrogen storage in the restored site was 2.8 and 1.9 times that in the soybean field, respectively. However, the SOC and TN storage in the 27-year restored site was 45.3% and 35.1% lower than that in the natural marsh, respectively. The SOC and TN content, bulk density, moisture content, clay, and plant belowground biomass significantly impact the SOC and TN storage (P