Vesicular–arbuscular mycorrhizas and the soil-disturbance-induced reduction of nutrient absorption in maize

II. Development of the effect



In previously reported studies, maize seedlings absorbed more phosphorus (P) from soil in a long-term zero-till system than from the same soil after disturbance. This partly resulted from greater vesicular-arbuscular (VA) mycorrhizal infection in the undisturbed soil. In the study reported herein, a growth room experiment was conducted to determine how long a soil must remain undisturbed before subsequent disturbance will reduce P absorption. Starting with disturbed soil, maize was grown for 3-week cycles. At the conclusion of each growth cycle, half of the pots were disturbed and replanted whereas the other half was replanted without disturbing. Over the three growth cycles, major increases in mycorrhizal infection in the plants in the undisturbed soil were observed concurrently with the increases in nutrient absorption.

A significant increase in P absorption occurred in the first growth cycle on undisturbed soil and greater increases occurred after the second and third. At 21 d in the third growth cycle, plants grown in the undisturbed soil had almost twice the dry weight of plants grown in the disturbed and had higher concentrations of N, P, Mg, Cu and Zn in the shoots. Absorption of P between 14 and 21 d of the third growth cycle in the undisturbed soil was 10 times larger than that in the disturbed soil. Absorption of N, Mg, Cu and Zn was more than three times larger. In the third growth cycle, concentrations of N, P, Mg and Zn in the shoot and intensity of VA mycorrhizal infection were greater in the undisturbed soil as early as 14 d after planting. There was a concurrent and rapid increase in VA mycorrhizal infection and P absorption by maize over three growth cycles when an initially disturbed soil was left undisturbed. This rapid concurrent development, particularly starting from an initially disturbed soil, provides good evidence that soil disturbance reduces VA mycorrhizal infection and hence P absorption by maize.