Although vesicular–arbuscular mycorrhizas (VAM) are abundant in natural ecosystems, the evidence for the mutualistic effect of this association under field conditions is conflicting. VAM infection and inflow of phosphorus, copper, zinc and manganese was measured in six co-existing plant species of a semi-natural grassland, during a 2-yr period, in order to establish whether patterns of nutrient uptake and plant growth in co-existing species can be related to levels of mycorrhizal infection. There was no relationship between VAM infection and shoot concentrations of P, Cu, Zn or Mn, or plant biomass, and only in a few cases was nutrient inflow related to infection.
Although the results do not support the hypothesis that VAM infection is beneficial for plant nutrition, high levels of P inflow do occur at certain periods during the growth season, suggesting that mycorrhizas may promote plant nutrient uptake at these times. Owing to the abundance of VAM, the lack of speciation and high P inflows which can occur in the field, these mycorrhizal associations are likely to be mutualistic.
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