Ectomycorrhizal Fungal Strains Facilitate Cd Enrichment in a Woody Hyperaccumulator Under Co-Existing Stress of Cadmium and Salt

Cadmium (Cd) pollution occurring in salt-affected soils has become an increasing environmental concern in the world. Fast-growing poplars have been widely utilized for phytoremediation of soil contaminating heavy metals (HMs). However, the woody Cd-hyperaccumulator, × , is relatively salt-sensitive and therefore cannot be directly used to remediate HMs from salt-affected soils. The aim of the present study was to testify whether colonization of × with ectomycorrhizal (EM) fungi, a strategy known to enhance salt tolerance, provides an opportunity for affordable remediation of Cd-polluted saline soils. Ectomycorrhization with strains facilitated Cd enrichment in × upon CdCl exposures (50 μM, 30 min to 24 h). The fungus-stimulated Cd in roots was significantly restricted by inhibitors of plasmalemma H-ATPases and Ca-permeable channels (CaPCs), but stimulated by an activator of plasmalemma H-ATPases. NaCl (100 mM) lowered the transient and steady-state Cd influx in roots and fungal mycelia. Noteworthy, colonization partly reverted the salt suppression of Cd uptake in poplar roots. EM fungus colonization upregulated transcription of plasmalemma H-ATPases (, , ) and annexins (, , ), which might mediate Cd conductance through CaPCs. EM roots retained relatively highly expressed and , thus facilitating Cd enrichment under co-occurring stress of cadmium and salinity. We conclude that ectomycorrhization of woody hyperaccumulator species such as poplar could improve phytoremediation of Cd in salt-affected areas.