Effects of different soil pH and nitrogen fertilizers on Bidens pilosa L. Cd accumulation

Bidens pilosa L. was a Cd hyperaccumulator. This experiment determined the effects of different soil pH (adjusted by weak acid and alkali at 4.83, 6.81, and 7.84, respectively) and nitrogen ((NH₄)₂SO₄, Ca(NO₃)₂) on B. pilosa phytoextracting Cd in soil collected from a smelter (Cd concentration was 19.63 mg kg^-1). The results showed that the Cd concentrations in B. pilosa were significantly higher (p < 0.05) with soil pH 4.83 treatments than those of pH 6.81 and 7.84 ones. The Cd concentration of B. pilosa grown in pH 7.84 soil was significantly lower (p < 0.05) than that in pH 6.81 soil. The extractable Cd concentration in soil was decreased (p < 0.05) with the increase of pH. Under three different pH conditions, the rhizosphere pH of B. pilosa was basically 0.2 lower than that of pH in bulk soil respectively, indicating that the hyperaccumulator had a certain acidification effect on soil. Two kinds of nitrogen fertilizers (NH₄)₂SO₄ and Ca(NO₃)₂ had no significant difference (p < 0.05) on Cd concentrations of B. pilosa, which was probably caused by the acidification effect of its rhizosphere. The biomasses of B. pilosa were not affected (p < 0.05) by different pH of soil. The photosynthetic production, antioxidative enzymes, and lipid peroxidation change trends of B. pilosa were basically consistent with its biomasses. Generally speaking, B. pilosa showed high Cd accumulation potential and strong adaptability for different soil situations.