Life history strategies of arbuscular mycorrhizal fungi

Arbuscular mycorrhizal fungi (AMF) are part of a mutualism between Glomalean fungi and most angiosperm roots. Little is known about the life history strategies of the approximately 150 AMF species, so it is difficult to predict their community dynamics and their role in ecosystems. I examined the colonization and persistence strategies of AMF to test for distinct life history strategies. Using 21 AMF isolates in a green house experiment, I found three distinct colonization strategies: extensive root colonizers (Glomaceae), extensive soil colonizers (Gigasporaceae) and limited root plus limited soil colonizers (Acaulosporaceae). These three strategies reflect taxonomic differences among AMF at the family level. Glomaceae isolates typically colonized roots before the other isolates. Faster colonizers had more infective structures in their external mycelium and formed larger, more numerous infection units than slower colonizing AMF. Due to these differences, traditional measurements of AMF colonization based solely on root colonization will not be accurate for all AMF. Following soil disturbance, the extensive soil colonizers (Gigasporaceae) were more tolerant than other AMF due to differences in their propagule types (spores versus mycelium). AMF with extensive root colonization (Glomaceae) were usually better plant symbionts but host identity was also an important determinant of host response. Because of technical difficulties, the persistence strategies of AMF could not be examined. Marked variation in the 18SSU rDNA of AMF means that it will be difficult to use this region to identify AMF isolates in mixed cultures. My results provide a starting point for future considerations of AMF life history strategies and an initial, predictive basis for understanding their community dynamics.