Showing their mettle: Extraradical mycelia of arbuscular mycorrhizae form a metal filter to improve host Al tolerance and P nutrition

BACKGROUND: New evidence has shown that arbuscular mycorrhizal (AM) fungi can contribute to the aluminum (Al(3+) ) tolerance of host plants growing in acidic soils with phytotoxic levels of Al(3+) . The aim of this study was to investigate the role of AM fungi isolated from naturally occurring Al(3+) acidic soils in conferring host tolerance to Al(3+) toxicity in three wheat cultivars differing in Al(3+) sensitivity. The experiment was conducted in a soilless substrate (vermiculite/perlite, 2:1 v/v) using two Al(3+) -tolerant wheat genotypes and one Al(3+) -sensitive wheat genotype. The wheat was colonized with a consortium of AM fungi isolated from an Andisol, with or without Al(3+) at a concentration of 200 mumol L(-1) . RESULTS: The response of wheat to Al(3+) in the medium was dependent on both the plant genotype and AM colonization. The benefits of the AM fungi to the wheat cultivars included an increased P concentration and relatively low Al(3+) accumulation in the plants. This was achieved through two mechanisms. First, the metal-chelating capacity of the AM fungi was clear in two of the cultivars ('Tukan' and 'Porfiado'), in which the enhanced extraradical mycelium development was able to retain Al(3+) in the glomalin and hyphae. Second, the increased AM-induced acid phosphatase activity in the rhizosphere of the other cultivar ('Atlas 66') increased host nutrition possibly by hyphae-mediated nutrient uptake and glomalin-related soil protein. CONCLUSION: The results suggest that the role of AM fungi in cultivar-specific Al(3+) detoxification can be achieved by increased extraradical mycelial filters and enhanced bioavailability of P in the host rhizosphere. (c) 2019 Society of Chemical Industry.