Taxonomic basis for variation in the colonization strategy of arbuscular mycorrhizal fungi

Arbuscular mycorrhizal fungi (AMF) are important components of terrestrial communities but the basic ecology of individual AMF, including their colonization strategy, remains unclear. The colonizing behaviours of 21 AMF isolates from three families (Acaulosporaceae, Gigasporaceae and Glomaceae) were compared to test for a relationship between AMF taxonomy and colonization strategy. Both the rate and extent of colonization were considered by measuring percentage root colonization, root fungal biomass, soil hyphal length and soil fungal biomass over 12 wk. Most Glomaceae isolates colonized roots before Acaulosporaceae and Gigasporaceae isolates. The fastest colonizers were also often the most extensive. Taxonomic differences were apparent in the amount and proportion of fungal biomass found in roots vs in soil. Glomaceae isolates had high root colonization but low soil colonization, Gigasporaceae isolates showed the opposite trend whereas Acaulosporaceae isolates had low root and soil colonization. These results were similar for four different host plants. The results indicate that the colonizing strategies of AM fungi differ considerably and that this variation is taxonomically based at the family level. Arbuscular mycorrhizal fungal taxonomy therefore has a functional basis.