A numerical analysis of published field trials with vesicular-arbuscular mycorrhizal fungi

This paper presents a numerical analysis of 78 published field trials with vesicular-arbuscular (VA) mycorrhizal fungi. Increased VA mycorrhizal colonization of the roots of crops and pasture herbs, produced by inoculation with these fungi, resulted in yield increases of 37% on average. However, there was no relationship between the size of the increase in infection and the size of the increase in yield. In addition, in approximately one-fifth of the trials, yield of plants with higher infection was depressed. VA mycorrhizal fungi are abundant and widespread in the roots of plants in both agricultural and natural vegetation. It is concluded here that the function of these symbiotic associations in field ecosystems warrants further study, particularly in terms of the influence of the type and degree of host infection on plant nutrient uptake and yield. For the present, direct evidence for a mutualistic function of VA mycorrhizal symbioses in the field is scant.