VESICULAR-ARBUSCULAR MYCORRHIZAS AND THE SOIL-DISTURBANCE-INDUCED REDUCTION OF NUTRIENT ADSORPTION IN MAIZE .3. INFLUENCE OF P AMENDMENTS TO SOIL

Maize seedlings have been shown to absorb more phosphorus (P) from soil from long term zero‐till plots than from the same soil after disturbance, apparently because of greater vesicular‐arbuscular (VA) mycorrhizal colonization in the undisturbed soil, A growth room experiment was conducted to determine the effect of soil P availability on this phenomenon. Maize was grown for three 3‐week cycles in initially disturbed soil. Phosphorus was mixed with the soil to create five P‐amendment rates: 0, 40, 80, 120, and 160 μg Pg−1soil. After each growth cycle, the soil in half the pots was disturbed and replanted, whereas the other half were replanted without disturbing the soil. In the third growth cycle, shoot dry weights were greater in the undisturbed soil than in the disturbed soil at the lower P‐amendment rates, but soil disturbance had no effect at the 120 and 160 μg P g−1 soil amendments. Mycorrhizal colonization was much greater in the undisturbed soil at all P amendment rates. Shoot N, P, Mg, and Zn concentrations were higher in the undisturbed than in the disturbed soil at all P amendments, but only the increased P and Zn could be directly related to increased mycorrhizal colonization. While the benefit to the plant from mycorrhizal colonization induced by lack of soil disturbance can be quite large even at high rates of P amendment to the soil, the benefit achieved depends on the balance between the carbon (C) cost and P benefit to the host and may or may not favour the host. Copyright © 1990, Wiley Blackwell. All rights reserved