Testing life history and trait-based predictions of AM fungal community assembly

• AM fungal life history strategies have been observed, but remain untested in the field.
• AM fungal communities differed between logged and undisturbed old-growth forests.
• However, no consistent indicators of either undisturbed or disturbed habitats were observed.
• The current paradigm for life history strategies of AM fungi warrants re-examination.

Arbuscular mycorrhizal (AM) fungal disturbance response is thought to be moderated by life history strategies (LHS). Research suggests that disturbance-tolerant taxa may be represented by fungi in the Glomerales, those in culture collections, and by cosmopolitan taxa due to their generalist growth habit. The corollary is that these taxa should be less common in undisturbed systems. Although widely accepted, these ideas originate from research conducted in previously disturbed systems. Whether they hold up to comparisons of disturbed versus undisturbed systems remains to be seen.We addressed this question by surveying logged and intact sites within forests dominated an AM fungal host (western redcedar; Thuja plicata). We predicted that old-growth sites would host fewer taxa from the Glomerales, fewer cultured taxa, and fewer cosmopolitan taxa compared to logged sites.Contrary to our predictions, the logged and intact sites did not differ with respect the putative disturbance-tolerant taxa. However, taxonomic composition differed, driven primarily by variation in relative abundance rather than loss or gain of taxa. Multiple analyses of indicator taxa revealed no consistent indicators of either undisturbed or disturbed habitats.Based on these findings, the current paradigm for a phylogenetically based LHS of AM fungi warrants re-examination.