EVIDENCE FOR DIFFERENTIAL RESPONSES BETWEEN HOST FUNGUS COMBINATIONS OF VESICULAR ARBUSCULAR MYCORRHIZAS FROM A GRASSLAND

The increase in spore density over that in the soil of an indigenous vesicular-arbuscular (VA) mycorrhizal community was measured in five plant species, after inoculation with the same soil (Experiment 1), and in pots containing individuals of the same species, which had been removed from the field site (Experiment 2). In Experiment 1, significant increase in spore density was observed for Glomus constrictum with Plantago lanceolata although increases in density were not observed for this fungus with other host species. Results of Experiment 2 were consistent for the combination of Plantago lanceolata and Glomus constrictum and the numbers of Acaulospora laevis spores, in pots containing Holcus lanatus or Rumex acetosa, were significantly higher than in the soil of the field site. The results do not support or oppose the hypotheses that either multiple infection or selectivity of VA mycorrhizas occur between certain combinations of host-fungus in co-existing plants of a natural community. The results indicate that VA mycorrhizal fungi respond differently according to the host species and thus such differences could result in selection pressures which favour certain