ABSTRACT

In laboratory microcosm experiments, co-occurring plant species were found to support very different rates of sporulation of arbuscular mycorrhizal (AM) fungi. These differences were not affected by the time of harvest, suggesting that they reflect host-dependent differences in fungal growth rates, rather than host-dependent timing of sporulation. Spore counts in field soil and estimates from sorghum trap cultures showed that the association of AM fungi with particular host plants in the field was positively correlated with the sporulation rates observed on those hosts in the microcosm experiments. The AM fungal species richness observed at the field site was high relative to estimates made in previous studies. Twenty-three distinct species of AM fungi were found, seven of which have not been previously described. The host-dependence of the relative growth rates of fungal populations may play an important role in the maintenance of fungal species diversity.