Does the mycorrhizal mediation hypothesis capture biogeographical patterns in plant-soil feedback? the case of conspecific negative density dependencies

CNDDs are thought to be stronger in AM-associating than ECM-associating trees.Most of the studies on CNDNs have been carried out in temperate systems.Mycorrhizal propagule constraints could exacerbate CNDNs of AM-trees at high latitudes.As a result overgeneralizations of existing findings on CNDNs could be precarious.Conspecific negative density dependencies (CNDDs) foster biodiversity through reducing the chances of competitive exclusion in plant communities and have therefore fascinated ecologists. A major driver of CNDDs is plant-soil feedback, and a lot of the literature assumes that the triggers of CNDDs concur with those for plant-soil feedback. Here, we suggest that a core assumption of a lot of the literature on CNDDs, that CNDDs are stronger in AM-associated than ECM-associated trees, is not quite as well supported as widely claimed. We think that dismissing this very important consideration prevents us from identifying a major gap in the literature on CNDDs. The vast majority of the literature on mycorrhiza-induced CNDDs originates from temperate systems, but the findings are extrapolated across divergent ecosystems. We then develop the argument that likely propagule limitations for arbuscular mycorrhizal trees in temperate forests might be inducing stronger CNDDs than they do at propagule sufficiency, which arbuscular mycorrhizal trees usually experience in other systems. We are thus contributing a new hypothesis in the field of mycorrhizal ecology with the potential to unify observations across scales and biomes.