Response of mycorrhizal symbiosis to phosphorus and its application for sustainable crop production and remediation of environment

ABSTRACT Mycorrhizal fungi symbiotically associate with 80% of land plants, extend extraradical hyphae in the soil, and promote phosphorus (P) uptake in host plants. It is necessary to utilize the function of mycorrhizal symbiosis to cope with future depletion of P resources. Elucidation of the mycorrhizal colonization mechanism for utilizing mycorrhizal fungi, inoculation methods in agriculture and forestry, and new function of extraradical hyphae are described. Root exudates from P-deficient plants promoted extraradical hyphal growth and a hydrophobic fraction of the exudates promoted the formation of appressorium and subsequent colonization of the roots. Inoculation with a mycorrhizal fungus at the nursery stage reduced phosphate fertilizer application in Welsh onion cultivation and thus production cost. Inoculation with ectomycorrhizal and arbuscular mycorrhizal fungi increased the growth of tropical tree species under nursery and field conditions. Acid phosphatase was secreted from the extraradical hyphae of Rhizophagus clarus and its activity was increased under low P conditions. We found that utilization of AM fungi is useful as a strategy for sustainable P resource use.