Effects of soluble phosphate fertilizer on Zn/Cd phytoextraction and nutrient accumulation of Sedum alfredii H. in co-contaminated soil

Improving the efficiency of phytoextraction is crucial for its successful application in phytoremediation technology practices. Fertilizer can increase plant biomass and change in phytoavailable soil elements, and is necessary strength in measurement of phytoremediation of contaminated soils. Mineral nutrition affects plant growth and metal absorption and subsequently accumulation of heavy metals through hyper-accumulator plants. This study assessed the effects of di-hydrogen phosphate (KH2PO4, Ca (H2PO4)2, NaH2PO4 and NH4H2PO4) applications (P2O5 22, 88 and 352 mg/kg soil) on growth, metal uptakes and nutrient contents of Sedum alfredii on aged zinc/cadmium (Zn/Cd) co-contaminated paddy soils. The addition of phosphates increase dry matter yield significantly at the phosphorus (P) supply level of P2O5 352 mg/kg (P0.05). The shoot P and Zn concentrations are enhanced significantly (P0.05), while the Cd concentration is decreased with the increase of phosphate levels. The phosphate application reduces N, the secondary nutrients (Ca, Mgand S) and micronutrients (Mn, Fe and Cu) concentrations, while the potassium (K)concentration has no significant effect except for NaH2PO4 treatment at P2O5 352 mg/kg. The total carbon concentration of shoots is increased at the high P level. The addition of P increases the amounts of Zn phytoextracted by S. alfredii at 88 and 352 mg/kg P2O5, significantly, and increases Cd significantly only at higher P levels (P0.05) after one clipping. The highest phytoextraction of Zn and Cd was observed in case of KH2PO4 and NH4H2PO4 treatments at P2O5 352 mg/kg. These results suggest that application of P fertilizers can increase bio-fixed amount of carbon, enhance removal of Zn and Cd from co-contaminated soils by S. alfredii, and shorten the time needed for accomplishing remediation goals.