Forms and vertical distributions of soil phosphorus in newly formed coastal wetlands in the Yellow River Delta estuary

To study the forms and vertical distributions of soil phosphorus (P) in a newly formed coastal wetland in the Yellow River Delta estuary, China, two transects from the Yellow River bank to the bare beach that encompassed a variety of vegetation covers were selected for soil sampling and field monitoring. A modified sequential fractionation method was used to partition the soil P, and the related properties were measured. The soils in this newly formed estuarine coastal wetland, only covered by salt-tolerant plant communities, are strongly alkaline (pH 8.4-9.2) with high soil salinity (mean, 6.23 parts per thousand). The content of total P (Pt) ranged from 548.3 to 728.5 mg kg(-1) in these soils. Dil.HCl-P-i (extracted with 1 M HCl) was the highest P fraction (mean, 58.1-72.8%), whereas NaHCO3-P-i was the lowest fraction (mean, 0.4-1.7%) of all the P forms. Vertical distributions showed a surface accumulation of Resin-P. Resin-P, NaHCO3-P-i, NaOH-P-i, and Conc.HCl-P-i (extracted with 11.3 M HCl) were positively or negatively correlated with some properties. Attributed to the spatial deposition and hydrology, Dil.HCl-P-i presented a poor correlation with Ca. The results also showed some clear differences in the P forms and P availability among vegetation covers. The vegetation cover could modify the soil quality, and Suaeda heteroptera, as the pioneer plant community species, significantly enhanced the freely exchangeable P-i and increased P availability, providing important ideas for salt-soil sustainable use.