AMF Inoculation Alleviates Molybdenum Toxicity to Maize by Protecting Leaf Performance

The use of arbuscular mycorrhizal fungi (AMF) is a vital strategy for enhancing the phytoremediation of heavy metals. However, the role of AMF under molybdenum (Mo) stress is elusive. A pot culture experiment was conducted to explore the effects of AMF (Claroideoglomus etunicatum and Rhizophagus intraradices) inoculation on the uptake and transport of Mo and the physiological growth of maize plants under different levels of Mo addition (0, 100, 1000, and 2000 mg/kg). AMF inoculation significantly increased the biomass of maize plants, and the mycorrhizal dependency reached 222% at the Mo addition level of 1000 mg/kg. Additionally, AMF inoculation could induce different growth allocation strategies in response to Mo stress. Inoculation significantly reduced Mo transport, and the active accumulation of Mo in the roots reached 80% after inoculation at the high Mo concentration of 2000 mg/kg. In addition to enhancing the net photosynthetic and pigment content, inoculation also increased the biomass by enhancing the uptake of nutrients, including P, K, Zn, and Cu, to resist Mo stress. In conclusion, C. etunicatum and R. intraradices were tolerant to the Mo stress and could alleviate the Mo-induced phytotoxicity by regulating the allocation of Mo in plants and improving photosynthetic leaf pigment contents and the uptake of nutrition. Compared with C. etunicatum, R. intraradices showed a stronger tolerance to Mo, which was manifested by a stronger inhibition of Mo transport and a higher uptake of nutrient elements. Accordingly, AMF show potential for the bioremediation of Mo-polluted soil.