Effective stimulation of phytoremediation of Amaranshus mangostanus L. in cadmium contaminated soils through reasonable phosphorous fertilizer rate

Objectives Soil property and chemical fertilization affect the remediation of plants to heavy metal contaminated soil. This study investigated the effects of different phosphate fertilizer rates on cadmium (Cd) absorption and accumulation of plants, aiming to provide reference through reasonable nutrient management.

Methods Amaranth (Amaranshus mangostanus L.) was used as the test material, and yellow brown soil and lateritic red soil were used in a pot experiment. Adding CdCl₂∙2.5H₂O of (analytical grade), and standing for one month were to simulate Cd polluted soil (Cd 15 mg/kg soil). Five P levels were setup as: 0 (CK), 50, 100, 200 and 400 mg/kg soil, using ammonium dihydrogen phosphate (analytical grade) as P source. After growing for 45 days, amaranth was harvested, the biomass of shoot and root were weighed, and the P and Cd contents were measured. Soil DTPA extracted available Cd content was measured as well.

Results P addition in soil increased the biomass of amaranth significantly. Compared with CK, the biomass of shoots and roots of amaranth were increased by 9.2%−39.0% and 4.0%−15.0% in yellow-brown soil, and by 7.7%−46.0% and 10.0%−100.0% in lateritic red soil. The Cd contents in the shoots and roots were decreased by 7.4%−50.2% and 7.9%−58.8% in yellow-brown soil, and by 9.9%−55.8% and 21.7%−66.0% in lateritic red soil; however, the Cd accumulation of amaranth in the shoots and roots were increased by 36.2%−54.3% and 7.4%−38.9% in yellow-brown soil, and by 34.3%−62.8% and 5.4%−55.4% in lateritic red soil. The total Cd accumulation in amaranth reached the highest at P addition level of 50 mg/kg soil. P addition in soil significantly decreased the content of available Cd, and the decrease was 0.9%−7.2% in yellow-brown soil and 1.2%−7.9% in lateritic red soil. There was a negative correlation between the content of Cd and P in amaranth.

Conclusions The application of phosphate fertilizer could promote the growth of amaranth and decrease the available content of Cd in soil. Although application of P fertilizer significantly reduce Cd content in root and root of amaranth, significantly increased biomass can increase the total uptake and accumulation of Cd, thus effectively enhance the phytoremediation of Cd contamination soil. In both the tested soils and the Cd pollution level, adding 50 mg/kg soil of P shows the best improvements.