Arbuscular mycorrhizal fungi regulate plant mineral nutrient uptake and partitioning in iron ore tailings undergoing eco-engineered pedogenesis

Excess available K and Fe in Fe-ore tailings with organic matter and water-deficiencies may restrain plant colonization and growth, which hinders the formation of eco-engineered soil from these tailings for sustainable and cost-effective mine site rehabilitation. Arbuscular mycorrhizal (AM) fungi are widely demonstrated to assist plant growth under various unfavorable environments. However, it is still unclear whether AM symbiosis in tailings amended with different types of plant biomass, and under different water conditions could overcome the surplus K and Fe stress for plants in Fe ore tailings, and if so, by what mechanisms. Here, host plants (Sorghum spp. Hybrid cv. Silk) either colonized or non-colonized by the AM fungi (Glomus spp.), were cultivated in Lucerne hay- (C: N ratio of 18, LH) or Sugarcane mulch- (C: N ratio of 78, SM) amended Fe-ore tailings under well-watered (55% water holding capacity (WHC) of tailings) or water-deficient (30% WHC of tailings) conditions. Mycorrhizal colonization, plant growth, and mineral elemental uptake and partitioning were examined. The results indicated that AM fungal colonization improved plant growth in tailings amended with plant biomass under water deficient conditions. AM fungal colonization enhanced plant mineral element uptake, especially P, both in the LH- and SM-amended tailings regardless of water condition. Additionally, AM symbiosis development restrained the translocation of excess elements (i.e., K and Fe) from roots to shoots, thereby relieving their phytotoxicity. AM roles in phosphorus uptake, and excess elemental partitioning were greater in tailings with LH amendment than those with SM amendment. Water deficiency weakened AM fungal colonization and functions in terms of mineral element uptake and partitioning. These findings have highlighted the vital role AM fungi played in regulating plant growth and nutrition status in Fe-ore tailings technosols, providing the basis for involvement of AM fungi in the eco-engineered pedogenesis of iron ore tailings.