Dynamics of soil biogenic element in Phragmites australis wetlands in intertidal zone in the Yellow River Estuary

Wetland soil serves as source, sink and transfer conduit of biogenic elements．Soil profiles to a depth of 50 cm in Phragmites australis wetlands in intertidal zone in the Yellow River Estuary were collected at levels of 0-10, >10-20, >20-30 and >30-50 cm in three sampling seasons (summer, autumn and spring)．The spatio-temporal dynamics and influencing factors of contents and stocks of biogenic elements including total nitrogen (TN), total phosphorus (TP), total sulfur (TS) and total potassium (TK) were examined．TN and TS contents in the top 50 cm soil were found to range from 68.19-421.29 mg·kg⁻¹ and from 356.15-935.77 mg·kg⁻¹, respectively．Contents were the highest in surface-soils, the highest in the spring among the three sampling seasons．TP contents were found to vary from 379.80-728.30 mg·kg⁻¹, with more uniform distributions, but with the highest content in summer season．TK contents varied from 17 852.41-23 265.30 mg·kg⁻¹, with no obvious profile distribution．Total nitrogen stocks (TNS) in the top 50 cm soil were found to be 109.66-227.36 g·m⁻², total phosphorus stocks (TPS) 350.74-625.27 g·m⁻², total sulfur stocks（TSS）331.15-575.70 g·m⁻², total potassium stocks (TKS) 12220.77-19780.33 g·m⁻²．Biogenic element stocks were mainly concentrated in the top 30 cm soil．TNS followed the order of summer, spring, autumn, while TPS and TKS followed the order of summer, autumn, spring ( P < 0.05)．TSS in spring was lower than in summer and autumn．Redundancy analysis and correlation analysis showed that total soil carbon, electrical conductivity, Mg and Al were closely related to contents of biogenic elements．It is concluded that total carbon content and carbon-nitrogen ratio were important factors influencing TNS．Bulk density, moisture content and electrical conductivity were important factors affecting TPS．