Host-specificity of AM fungal population growth rates can generate feedback on plant growth

While the mutualistic interaction between plants and AM fungi is of obvious importance to ecosystem processes, the factors influencing the ecological and evolutionary dynamics within this interaction are poorly understood. The mutual interdependence of plant and AM fungal relative growth rates could generate complex dynamics in which the composition of the AM fungal community changes due to association with host and this change in fungal composition then differentially feeds back on plant growth. I first review evidence for feedback dynamics and then present an approach to evaluating such complex dynamics. I specifically present evidence of host-specific differences in the population growth rates of AM fungi. Pure cultures of AM fungi were mixed to produce the initial fungal community. This community was then distributed into replicate pots and grown with one of four co-occurring plant species. Distinct compositions of AM fungal spores were produced on different host species. The AM fungal communities were then inoculated back onto their own host species and grown for a second growing season. The differentiation observed in the first generation was enhanced during this second generation, verifying that the measure of spore composition reflects host-specific differences in AM fungal population growth rates. In further work on this system, I have found evidence of negative feedback through two pairs of plant species. The dynamic within the AM fungal community can thereby contribute to the coexistence of plant species.