THE ROLE OF VA MYCORRHIZAE IN THE ABSORPTION OF P AND Zn BY MAIZE IN FIELD AND GROWTH CHAMBER EXPERIMENTS

Abstract

Two years of field experiments and one growth chamber experiment were conducted to determine the role of VA mycorrhizae in P and Zn absorption as well as the P-Zn interaction. The pattern of development of vesicular-arbuscular mycorrhizae (VAM) in the early growth stages of maize (Zea mays L.) plants in southern Ontario, Canada was investigated. The field experiments consisted of three fertility treatments, recommended phosphorus (RP), high phosphorus (HP) and HP plus zinc (HPZn). The RP and HP soils were used in the growth chamber experiment and Zn fertilizer was added to both RP and HP soils to have treatments of RP, HP, RPZn and HPZn. Benomyl was used in the second year of the field experiment and in the growth chamber experiment to reduce mycorrhizal infection. In the field experiment in 1987, 20% of the roots were colonized by VAM in the RP soil just 3 wk after sowing. At 40 d after sowing, about 50% of roots were infected. The HP treatment significantly reduced VAM infection intensity compared to the RP treatment. The addition of 40 kg Zn ha⁻¹ to the HP soil had little effect on mycorrhizal infection intensity in either field or growth chamber experiments. However, Zn fertilization increased mycorrhizal infection in the RP treatment in the growth chamber experiment. Treatment with benomyl significantly decreased mycorrhizal infection, shoot dry weight, P concentration and P inflow in the RP soil, suggesting the fungal relationship is important for P absorption in this soil. There was no conclusive evidence that mycorrhizae are important for P absorption in the HP soil. Although HP treatment decreased VAM infection greatly in both field and growth chamber experiments, it did not affect the absorption of Zn. Benomyl did not affect the shoot Zn concentration in either field or growth chamber experiments, suggesting that mycorrhizae are not important in the absorption of Zn on this soil. Key words: VAM infection development, maize, P, Zn, benomyl