Invasive trees rely more on mycorrhizas, countering the ideal‐weed hypothesis

Abstract

The ideal weed hypothesis predicts that invasive plants should be less dependent on mutualisms. However, evidence in favor or against this hypothesis comes mainly from observational studies. Here, we experimentally tested this hypothesis using a two-factor greenhouse experiment, comparing the seedling growth response of different Pinus species (varying in invasiveness) to ectomycorrhizal fungal inoculation. Most species showed no response until they were six months old, at which point inoculation increased growth between 10% and 260% among the different species. This growth response was higher for species with lower seed mass, higher dispersal ability, higher Z score (a proxy for invasiveness) and higher number of naturalized regions, all of which correspond to higher invasiveness. Our results show that timing is a crucial factor when comparing mycorrhizal dependecy of different species. Dependence on mutualistic microorganisms could be part of a strategy in which invasive species produce smaller seeds, in greater number, which can disperse further but where seedlings are more reliant on mycorrhizas to improve access to water, nutrients, and protection from pathogens. Our results suggest that reliance on mutualisms may enhance, rather than limit, non-native species in their ability to spread, establish and colonize.

The root‐associated arbuscular mycorrhizal fungal assemblages of exotic alien plants are simplified in invaded distribution ranges, but dominant species are retained: A trans‐continental perspective

“…In novel environments, the AMF have the potential to alter nutrient acquisition strategies and decrease requirements for the presence of specialized nutrient acquisition strategies of invasive plants (Palma et al, 2017). On the other hand, invasive plants might be less dependent on generalist AMF in their exotic ranges (Seifert et al, 2009), although the reverse has been reported for several species of trees (Moyano et al, 2020; Moyano et al, 2021). However, invasive plants that colonize disturbed areas may obtain, or require, fewer benefits from their AMF partners as long as resources are readily available (Jasper et al, 1989).…”

Development of negative soil feedback by an invasive plant near the northern limit of its invaded range

“…However, any differences in these elements were weak, and multivariate analyses indicated substantial overlap between invaded and uninvaded sites. These results do not suggest that substantial chemical differences between soils explain their invasion status, as might be expected given that paired plots were chosen to be as similar as possible; however, it is possible that L. vulgaris itself may modify the chemistry of plots where it is established, as has been shown for other invaders (Liao et al 2008 Measuring effects of the entire soil community integrates the effects of both antagonists (nematodes, bacteria, and fungal pathogens including inappropriate mycorrhizal partners) and mutualists (mycorrhizae, bene cial rhizosphere bacteria) in soil, and invasive species can depend on mutualistic microorganisms, such as mycorrhizal fungi, in the invaded range (Moyano et al 2021). Therefore, the relatively more positive effect of sterilization in invaded soils compared to uninvaded soils in principle could result from either the removal of soil pathogens from invaded soils or the removal of mutualists from uninvaded soils.…”

“…For the rst greenhouse iteration, individuals were left to grow for 6 weeks, and plant height (cm) was measured every seven days. This length of time was su cient to allow plants to reach maturity and ower, which is desirable since effects of soil pathogens may change over maturation from seedling to adulthood (Moyano et al 2021). Plants were evenly watered every 3 days, and containers were shu ed every week within the greenhouse chamber.…”

Diaspore traits specialized to animal adhesion and sea current dispersal are positively associated with the naturalization of European plants across the world

“…In the case of anemochorous plants, although there are abundant cases of non‐native species within this LDD syndrome, their naturalization success could be related to factors other than dispersal syndrome. For example, if we consider the Pinus genus, whose species have anemochorous diaspores (some widely naturalized) (Essl et al 2010), their invasiveness has been explained by different aspects, such as a high introduction effort (Essl et al 2010, McGregor et al 2012), high climate matching (Essl et al 2011, McGregor et al 2012), high and continuous seed output (Richardson et al 1990, Rejmánek and Richardson 1996) or their mutualistic symbiosis with ectomycorrhizal fungi (Moyano et al 2020, 2021). Further, while most Pinus species are anemochorous (with very few exceptions), only a few species are invasive (Grotkopp et al 2004).…”