Reasonable mowing and nitrogen fertilization promote chromium remediation by the hyperaccumulator Leersia hexandra Swartz

Abstract

Abstract Leersia hexandra Swartz, is a chromium (Cr) hyperaccumulator, but the potential for continuous remediation or reasonable mowing and nitrogen fertilization pattern has not been fully characterized. This study aimed to investigate the Cr remediation by L. hexandra under reasonable mowing and nitrogen fertilization patterns using hydroponic experiments. The mowing heights (no mowing, CK; the shoots were reserved for 0, 5 and 10 cm), mowing time (CK; the shoots were mowing after 30, 60, 90 and 120 days), mowing frequencies (CK; the shoots were mowing for 1, 2 and 3 times) and concentrations (42, 84 and 168 mg/L) of nitrogen fertilization (calcium nitrate, ammonium sulfate, and urea) have effects on biomass, Cr concentration and accumulation in shoots of L. hexandra. The results show that the highest biomass (67.0 g) and Cr accumulation (5.33 mg/pot) of L. hexandra found at mowing pattern (10 cm, 90 days, three times), which were increased by 91.4%, and 36.0% compared to CK, respectively. The addition of 84 mg/L ammonium sulfate significantly increased (p < 0.05) the biomass and Cr accumulation of L. hexandra. In addition, the contents of hormones GA3, 6-BA, 6-KT, TZR and JA in leaves were significantly increased under reasonable mowing and nitrogen fertilization treatments, while IPA and JA in stems. In conclusion, the study results have shown that reasonable mowing and nitrogen fertilization are effective options for improving the continuous phytoremediation of Cr-contaminated.