Arbuscular Mycorrhizas: Drivers or Passengers of Alien Plant Invasion

Abstract

Observational and manipulative studies have revealed that alien plant invasions are an outcome of interplay between a myriad of biotic and abiotic factors operating at various spatio-temporal stages and scales. Despite the salient role of ubiquitous arbuscular mycorrhizal (AM) fungi in plant interactions, studies exploring the role of such symbionts in invasiveness of alien species and invasibility of communities are limited, in part because of difficult-culturablilty of AM fungi on artificial media and apparent complexities in manipulations of AM-plant interactions in field and laboratory experiments. Moreover, analysis of the AM-plant invasion studies conducted so far have yielded contradictory results with some indicating facilitation of invasion by AM fungi and others its inhibition. Other studies have indicated that arbuscular mycorrhizal symbiosis has no effect on invasiveness of alien plants. While arbuscular mycorrhizas may facilitate invasiveness of some alien plants, such plants may also potentially impact mycorrhizal community structure and functions in the invaded habitats in different ways. The present review addresses these paradoxically conflicting observations in the context of mutualismcommensalism-parasitism gradient that characterizes the relationship between AM fungi and their alien vs. native hosts and also discusses the influence of alien invasive plants on mycorrhizal community structure of invaded ecosystems. Through critical analysis of costs and benefits for invasive plants that associate with AM fungi in their introduced range, invasion-induced shifts in AM mutualism are evaluated in the context of their impact on native biodiversity. Underlining limitations of methodologies and experimental designs usually employed to understand AM-mediated plant invasiveness, we proposes herein some alternative frameworks and experimental approaches to overcome these limitations.

Invasive plants affect arbuscular mycorrhizal fungi abundance and species richness as well as the performance of native plants grown in invaded soils

“…Invaders that are non-mycorrhizal or have low symbiotic dependency can inhibit AMF, therefore reducing the competitiveness of native plants that rely on AMF. In contrast, invaders that are more dependent on mycorrhizal association may modify the AMF abundance and species richness and as a consequence, receive greater benefits from it than native plant species (Shah et al 2009). …”

“…Yuan et al (2014) provided indirect evidence that the secondary metabolites of a mycorrhizal invader in China, Solidago canadensis, selectively impact on the composition of AMF community by enhancing the most beneficial AMF and inhibiting less favorable ones. Third, plant invasions through their influence on soil properties may indirectly affect composition of AMF communities that in turn can translate into the success of invasive species (Shah et al 2009). As revealed by our investigation, the invasions of plants under study significantly changed some chemical soil properties, e.g., decreased P content and increased C:P ratio, whereas R. japonica increased N-NO 3 -concentration (Stefanowicz et al, unpublished).…”

“…They are also crucial for the protection of plants against biotic (pathogens) and abiotic (drought, heavy metal toxicity) stresses and have been found to determine plant community composition and function (Smith and Read 2008). The changes in AMF abundance and species richness caused by alien plants can thus be detrimental to native plant species and accelerate plant invasions (Reinhart and Callaway 2006;Shah et al 2009). …”

“…Moreover, there is no doubt that invasive plants alter soil microbiological properties, but directions of the changes and their magnitude may differ between habitats. As it was underlined by Shah et al (2009) and Lekberg et al (2013), the comparisons of effects of multiple plant species invading different habitats have been neglected so far. Therefore, we investigated the effects of invasions of three transformers, namely Reynoutria japonica Houtt.…”

Arbuscular mycorrhizal colonisation of roots of grass species differing in invasiveness

“…Although invasive plants may benefit from mutualistic relationships such as AMF symbioses (Richardson et al 2000, Shah 2009b, it has been hypothesized that exotic plants without obligate dependence on an AMF symbiont have greater chance to become invasive in the new community compared to those with strong AMF associations (Pringle et al 2009). The carbon cost of sharing assimilates with mycorrhizal fungi can be quite high (Douds et al 1988).…”