How a functional soil animal-earthworm affect arbuscular mycorrhizae-assisted phytoremediation in metals contaminated soil?

Phytoremediation is a promising and sustainable technology to remediate the risk of heavy metals (HMs) contaminated soils, however, this way is limited to some factors contributing to slow plant growth and low remediation efficiency. As soil beneficial microbe, arbuscular mycorrhizal fungi (AMF) assisted phytoremediation is an environment-friendly and high-efficiency bioremediation technology. However, AMF-symbiotic formation and their functional expression responsible for HMs-polluted remediation are significantly influenced by edaphic fauna. Earthworms as common soil fauna, may have various effects on formation of AMF symbiosis, and exhibit synergy with AMF for the combined remediation of HMs-contaminated soils. For now, AMF-assisted phytoremediation incorporating earthworm coexistence is scarcely reported. Therefore, the main focus of this review is to discuss the AMF effects under earthworm coexistence. Effects of AMF-symbiotic formation influenced by earthworms are fully reviewed. Moreover, underlying mechanisms and synergy of the two in HMs remediation, soil improvement, and plant growth were comprehensively elucidated. Phenomenon of "functional synergism" between earthworms and AMF may be a significant mechanism for HMs phytoremediation. Finally, this review analyses shortcomings and prescriptions in the practical application of the technology and provides new insights into AMF- earthworms synergistic remediation of HMs-contaminated soils.