Changes in the storage of soil biogenic elements across different restoration years in the Xianghai degraded wetland

Wetland restoration through plant transplantation has been shown to positively influence the accumulation and stability of soil biogenic elements; however, there is limited understanding of the dynamic changes in these elements within typical plant communities of inland wetlands across varying restoration years. This study employed in situ field soil sampling to investigate the effects of different restoration years (one year, three and five years) on soil biogenic elements across distinct plant communities in typical inland wetlands, utilizing a space-for-time approach. The findings revealed that the contents of soil organic carbon (SOC) and total phosphorus (TP) were significantly greater in the Phragmites australis wetland compared to the Typha orientalis wetland, owing to the higher biomass of P. australis. The ratios of total nitrogen (TN) to TP and SOC to TP increased significantly in both T. orientalis and P. australis wetlands. The contents and densities of SOC and TP increased in both wetlands as restoration year progressed, which was linked to decreased soil temperature and increased soil moisture and bulk density. The content and density of TN also significantly increased in the P. australis wetland with longer restoration years, while those were higher in the T. orientalis wetland restored for three years, caused by the positive effect of lower soil temperature and minimal root disturbance. The contents and densities of SOC and TP were higher in the P. australis wetland than those in the T. orientalis wetland due to superior regulation of soil moisture and temperature. Our results suggest that prolonged restoration years enhance the content and density of soil biogenic elements, underscoring the importance of consideration of the duration of wetland restoration when evaluating the dynamics of soil carbon and nutrient accumulation in typical degraded inland marshes.