Performance of Acaulospora longula soil-inoculum grown under contrasting phosphorus supply on foliar antioxidant bioactivity of maize

It is known that phosphorus (P) availability can modulate the efficiency of arbuscular mycorrhizal fungi (AMF). Propagating AMF inoculants in a medium with high P rate may enable their use in agricultural systems with high P availability. However, the effect of this strategy on foliar antioxidant bioactivities remains unknown. This study aimed to investigate the role of a mycorrhizal isolate, cultivated in a substrate with a high P rate, on the foliar antioxidant capacity of maize ( Zea mays L.) grown in a P-supplemented substrate. Acaulospora longula inoculum was cultivated at two P rates: low P [3μM KH 2 PO 4 ] and high P [15μM KH 2 PO 4 ] and then used to inoculate maize grown in a substrate with (39mg P dm -3 ) or without (22mg P dm -3 ) P addition. After 70 days, in vitro antioxidant activity was evaluated using DPPH and ABTS radicals, as well as the ferric reducing power and the phosphomolybdenum complex assay, along with the production of proteins, flavanones and dihydroflavonols, and total saponins in maize leaves. The A. longula soil-inoculum cultivated in high-P substrate was effective in increasing, by more than 100%, the in vitro antioxidant potential and the production of foliar flavanones and dihydroflavonols in maize grown in the unfertilized substrate. On the other hand, the fungus cultivated in the low-P substrate showed similar performance under both phosphate fertility conditions (39mg P dm -3 and 22mg P dm -3 ), with increments ranging from 24% to 150% in foliar antioxidant activity compared to the non-inoculated plants. Thus, high-P-cultured inoculum has potential under low-P or unfertilized conditions and cannot be directly extrapolated to high-P agricultural soils.