Intercropping can accelerate the phytoremediation of Cd-contaminated soil

Remediation of heavy metal (HM)-contaminated farmland has attracted much attention. Intercropping shows great potential in the remediation of HM-contaminated farmland and has been extensively studied. However, it remains uncertain how intercropping influences phytoremediation. In this study, a meta-analysis was performed to evaluate the effects of intercropping on plant growth, plant Cd uptake, residual soil Cd concentration, and the related impact factors. The results showed that compared with monocropping, intercropping decreased plant biomass (-13.0 %) and Cd uptake (-26.9 %), whereas it increased Cd translocation factor (5.23 %) and soil pH (2.74 %). However, intercropping decreased residual soil Cd concentration by -2.08 % under the conditions of low plant biomass and less Cd uptake. These indicate that phytoextraction may contribute little to soil Cd removal in intercropping, and the indirect effects of intercropping are more important than its direct effects. Intercropping effects were affected by experimental and environmental factors. In terms of decreasing residual soil Cd concentration, intercropping produced large effect under at least one of the following conditions: monocots-dicots combination, intercropping with hyperaccumulator, in the soil contaminated by industrial pollution-derived Cd, at soil Cd level of ≤10.0 mg/kg, in acid soil (pH ≤ 6.50), and at the medium experimental duration of 61-120 d. This study confirms that intercropping can accelerate the phytoremediation of Cd-contaminated soil, and indirect effects of intercropping may play important roles.