Nitrogen application and mowings improve chromium phytoextraction efficiency of Leersia hexandra Swartz

Phytoextraction is a promising option for Cr-contaminated soil, but the long remediation period remains a primary hindrance to its large-scale application. This study is the first to assess the combined effects of nitrogen addition and mowings (NM) on the growth and Cr extraction of Leersia hexandra Swartz. A 1-year plot experiment was conducted, revealing that NM promoted the growth of L. hexandra. Compared to the control, NM significantly increased shoot biomass of L. hexandra by 111% (p < 0.05). The shoot biomass harvested from the second and third mowing sessions was 1.35 and 3.34 times higher than that from the first mowing session, respectively. In addition, chlorophyll content, root activity, and auxin content were significantly higher in NM treatment than those in control. These results indicate that a single addition of ammonium sulfate provides nutrients for L. hexandra shoot regeneration and maintains good growth after mowing. Furthermore, the extracted Cr amount in the shoot of NM reached 25.4 g/m2, an increase of 48.3% compared with control (p < 0.05). The soil Cr removal rate in NM was 1.85 times that of control (p < 0.001). These findings indicated that, compared with the phytoremediation technology using only L. hexandra, NM is a promising method for promoting Cr phytoextraction, suggesting its potential for large-scale ecological restoration at a lower cost.