The positive effects of arbuscular mycorrhizal fungi inoculation and/or additional aeration on the purification efficiency of combined heavy metals in vertical flow constructed wetlands

Inoculation with arbuscular mycorrhizal fungi (AMF) and additional aeration (AA), as two approaches to improve the functioning of treatment wetlands, can further promote the capacity of wetlands to purify pollutants. The extent to which, and mechanisms by which, AMF and AA purify wetlands polluted by combined heavy metals (HMs) are not well understood. In this study, the effects and mechanisms of AMF and/or AA on combined HMs removal in vertical flow constructed wetlands (VFCWs) with the Phragmites australis (reeds) were investigated at different HMs concentrations. The results showed that (1) AA improved the AMF colonization in VFCWs and AMF accumulated the combined HMs in their structures; (2) AMF inoculation and/or AA significantly promoted the reeds growth and antioxidant enzymes activities, thereby alleviating oxidative stress; (3) AMF inoculation and AA significantly enhanced the removal rates of Pb, Zn, Cu, and Cd under the stress of high combined HMs concentrations comparing to the control check (CK) treatment (autoclaved AMF inoculation and no aeration), which increased by 22.72%, 30.31%, 12.64%, and 50.22%, respectively; (4) AMF inoculation and/or AA significantly promoted the combined HMs accumulation in plant roots and substrates and altered the distribution of HMs at the subcellular level. We therefore conclude that AMF inoculation and/or AA in VFCWs improves the purification of combined HM-polluted water, and the VFCWs-reeds-AMF/AA associations exhibit great potential for application in remediation of combined HM-polluted wastewater.