Sediment phosphorus speciation and retention process affected by invasion time of Spartina alterniflora in a subtropical coastal wetland of China

In coastal wetland ecosystems, most phosphorus (P) accumulates in the sediments and becomes a major pollutant causing eutrophication by recycling to the water column in estuary areas, especially exotic plant invasions will change the nutrient cycling. In this study, a large wetland invaded by exotic species Spartina alterniflora for over 15 years was selected to study the sediment P fractionation and its retention for different plant invasion periods. The samples were collected from east to west in September and the sediment P was fractionated into total P (TP), inorganic P (IP), iron/aluminum-bound P (Fe/Al-P), calcium-bound P (Ca-P), and organic P (OP). Additionally, the effect of the invasion period on the wetland P fractionation based on space–time reciprocal principle was investigated. For different S. alterniflora invasion periods, the average TP concentration was 675.37 mg kg −1 with a range of 160.33–1071 mg kg −1 . The IP concentration was in the range of 107.33–813.33 mg kg −1 (accounting for 54.4–79.5% of TP), of which Fe/Al-P and Ca-P represented up to 99.4%. In addition, the P retention ( R P ) was within 41.67–329.67 mg kg −1 . We also found that TP, IP, Fe/Al-P, Ca-P, OP, and R P in sediments were negatively correlated with pH ( p