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

I. Causal relations



This study was designed to test the hypothesis that disruption of the macrostructure of a previously zero-tilled soil is capable of reducing vesicular-arbuscular (VA) mycorrhizal infection to a degree such that phosphorus (P) absorption is reduced. Undisturbed soil cores (within plastic cylinders) were excavated from long-term, zero-tilled plots. Soil removed from these plots, which was first subjected to structurally disruptive forces and then packed into identical cylinders, formed the disturbed comparisons. Maize (Zea mays L.), wheat (Triticum aestivum L.), spinach (Spinacea oleracea L.) or rape (Brassia napus L.) were grown in the cores and P and zinc (Zn) absorption patterns monitored.

Soil disturbance significantly reduced P and Zn absorption by maize grown in soil originating from three sites differing in local geography and/or texture. Disturbance also reduced mycorrhizal infection in the three soils.

A significant effect of disturbance upon the VA mycorrhizal infection of both maize and wheat roots (both mycorrhizal) and also upon the P absorption by these species was observed. None was found with respect to spinach and rape comparisons (non-mycorrhizal).

Injection of benomyl, a potent inhibitor of mycorrhizal fungi, into the soil surface significantly reduced the influence of soil disturbance upon P absorption. No significant differences were found in VA mycorrhizal infection within fungicide-treated cores.

We accepted our hypothesis based upon the above evidence.