Arbuscular mycorrhizal fungal hyphae mediating acidification can promote phytate mineralization in the hyphosphere of maize (Zea mays L.)

Mycorrhizal and non-mycorrhizal maize (Zea mays L.) plants were grown in two-compartment rhizoboxes, in order to study the effect of mycorrhizal hyphae-mediated acidification on organic P mineralization in the hyphosphere. The soil in the two compartments was supplemented with either KNO3 or (NH4)2SO4, and phytin (0 or 75 mg P kg−1) was added to the hyphal compartment. P content in the shoots was significantly higher for the NH4+ treatment than for the NO3− treatment, but only in the combined presence of phytin and AM fungal mycelium (Rhizophagus intraradices). NH4+ treatment under these conditions also led to a decrease in hyphosphere pH, enhanced phosphatase activity in the hyphosphere and accelerated mineralization of phytin compared to the NO3− treatment. The results show that hyphosphere acidification induced by absorption of NH4+ by the AM fungal mycelium leads to an increase in phosphatase activity, and consequently enhances mineralization of phytin and improves maize uptake of P from phytin-P.