Remediation efficacy of Sedum plumbizincicola as affected by intercropping of landscape plants and oxalic acid in urban cadmium contaminated soil

Abstract

Intercropping is a promising technique for remediation of soils contaminated with heavy metals. Organic acids can increase the availability of heavy metals in soil. Our aim was to assess the effect of oxalic acid as an activator for hyperaccumulator–landscape plant intercropping to efficiently restore contaminated soil with low cost. The hyperaccumulator plant (Sedum plumbizincicola) was intercropped with selected landscape plants: Oxalis corniculate (ground cover plant), Calendula officinalis (grass flower plant), and Buxus sinica (shrub). The effects of 11 mmol kg−1 oxalic acid treatment on growth and Cd accumulation capacity of Sedum plumbizincicola–landscape plants intercropping systems were evaluated in a 76-day pot experiment. Oxalic acid has increased the availability of Cd in soil. The biomass of Sedum, Oxalis, and Buxus plants was higher in treatment of oxalic acid than without oxalic acid. The biomass, chlorophyll, and catalase contents of Calendula were lower in treatment of oxalic acid than without oxalic acid, which indicated severe stress caused by enhanced availability of Cd. The malondialdehyde contents of Calendula and Buxus were higher in treatment of oxalic acid, which indicates that higher Cd availability has resulted damage of membrane. The free proline contents of Calendula and Buxus were higher in treatment of oxalic acid. The Cd content of Sedum plants was higher in treatment of oxalic acid than lower Cd in landscape plants with no application of oxalic acid. It is concluded that oxalic acid has a positive effect on remediation efficiency of Sedum plumbizincicola-Oxalis and Sedum plumbizincicola-Buxus intercropping systems. Oxalic acid has enhanced remediation efficiency of hyperaccumulator-landscape plants intercropping which has offered a new, useful and practical technique for remediation of urban soils with low-level Cd contamination.