Mycorrhizal co‐invasion and novel interactions depend on neighborhood context

Abstract

Abstract. Biological invasions are a rapidly increasing driver of global change, yet fundamental gaps remain in our understanding of the factors determining the success or extent of invasions. For example, although most woody plant species depend on belowground mutualists such as mycorrhizal fungi and nitrogen-fixing bacteria, the relative importance of these mutualisms in conferring invasion success is unresolved. Here, we describe how neighborhood context (identity of nearby tree species) affects the formation of belowground ectomycorrhizal partnerships between fungi and seedlings of a widespread invasive tree species, Pseudotsuga menziesii (Douglas-fir), in New Zealand. We found that the formation of mycorrhizal partnerships, the composition of the fungal species involved in these partnerships, and the origin of the fungi (co-invading or native to New Zealand) all depend on neighborhood context. Our data suggest that nearby ectomycorrhizal host trees act as both a reservoir of fungal inoculum and a carbon source for late-successional and native fungi. By facilitating mycorrhization of P. menziesii seedlings, adult trees may alleviate mycorrhizal limitation at the P. menziesii invasion front. These results highlight the importance of studying biological invasions across multiple ecological settings to understand establishment success and invasion speed.

Facilitation between woody and herbaceous plants that associate with arbuscular mycorrhizal fungi in temperate European forests

“…The respective (quartile) figures for herbaceous plants were 3%–7% (ECM) and 40%–49% (AM). The mycorrhizal mediation hypothesis has been tested several times with a focus on ECM plants and in most cases the data supported the hypothesis (e.g., Dickie, Guza, Krazewski, & Reich, 2004; Richard, Selosse, & Gardes, 2009; Teste et al., 2009; Moeller, Dickie, Peltzer, & Fukami, 2015) which appears to be due to ECM propagule limitation (Dickie et al., 2004; Dickie, Davis, & Carswell, 2012) . Despite our awareness that AM propagules decline in the forest compared to herbaceous systems (Fisher & Fulé, 2004), we know much less about the possibility that mycorrhizal mediation exists in temperate forests with regard to AM fungi.…”

Loss of functional diversity and network modularity in introduced plant-fungal symbioses

“…Nonetheless, the successful invasion of Pinus associating with a highly simplified fungal community suggests that even where there is a major reduction in mycorrhizal associates, trees may not be limited by a loss of symbiont diversity (Hynson et al 2013; Hayward et al 2015 b ). Furthermore, in some cases alien trees may form novel associations with fungal associates of native flora (Tedersoo et al 2007; Bahram et al 2013; Moeller et al 2015), or re-establish symbioses with cosmopolitan species (Dickie et al 2010). …”

“…The few studies of other alien ectomycorrhizal trees, including Eucalyptus (Diez 2005) , Pseudotsuga (Moeller et al 2015), Salix and Alnus (Bogar et al 2015) suggest that co-invasion with a reduced fungal community from the native range is widespread, although the identity of co-invading fungi may vary with alien tree identity.…”

“…This means that the presence of one plant species may support a population of fungi that serves as inoculum, facilitating the establishment of a second plant species. Shared fungal symbiont species have been observed between co-occurring alien Alnus and Salix (Bogar et al 2015), and between alien trees, Pinus and Pseudotsuga , and native trees in the Nothofagaceae (Dickie et al 2010; Moeller et al 2015), although the shared symbionts are generally only a small portion of total associations. Shared fungal symbiont species have also been observed between native trees and alien trees in plantations of Eucalyptus (Tedersoo et al 2007) and Pinus (Bahram et al 2013).…”

Research on mutualisms between native and non-native partners can contribute critical ecological insights

“…Non-native species acting opportunistically can be generalist mutualists under some contexts and cheaters under others; the non-native Japanese white-eye (Zosterops japonicus), for example, nectar-robs some endemic Hawaiian plant flowers but pollinates others . Recent evidence that Douglas fir (Pseudotsuga menziesii) invading New Zealand can readily form mutualisms with a diversity of native ectomycorrhizal fungi (Moeller et al 2015) runs counter to other ectomycorrhizal invasive plants in the Southern hemisphere whose associations appear restricted to cosmopolitan or coinvading fungi (Nuñez et al 2009;Dickie et al 2010;Bogar et al 2015). While no research has explored the network impact or stability of these interactions, we can logically predict that diverse associations may enhance stability.…”