New support for the Enhanced Mutualism Hypothesis for invasion

Author(s): Ylva Lekberg, Ragan M. Callaway

Abstract

Why are so many exotic plant species more abundant and have greater impacts in their nonnative than native ranges? Hypotheses that address this vexing question generally focus on variation in the intensity of negative interactions, such as escaping consumers or outcompeting natives in nonnative ranges (Jeschke, 2014). But in addition to these, some invasive species have shown a remarkable ability to capitalize on generalist mutualists in their nonnative ranges (Traveset & Richardson, 2014), and in some cases procure more or better mutualists than in their native ranges. This latter phenomenon was formalized as the Enhanced Mutualism Hypothesis (EMH; Reinhart & Callaway, 2004, 2006). In this issue of New Phytologist, Yu et al. (2022, pp. 1140–1153) ‘Greater chemical signaling in root exudates enhances soil mutualistic associations in invasive plants compared to natives’ show that interactions with arbuscular mycorrhizal (AM) fungi are more beneficial for exotic invasive species than related native species. This provides some of the most convincing support of the EMH to date. With an elegant set of experiments, Yu et al. show that: (1) exotic plant species invest more in producing and sending chemical signals to AM fungi than do native plants; (2) signals produced by nonnative plants are more effective at recruiting AM fungi to exotic plant roots than signals produced by native species, and most importantly; (3) recruiting more AM fungi corresponds with greater plant growth. Exotic invasive plant species out-perform natives in many ways (Inderjit et al., 2021), but if and how mutualism is involved in this superior performance remains an ecological frontier.

Citation

Lekberg, Y., & Callaway, R. M. (2022). New support for the Enhanced Mutualism Hypothesis for invasion. New Phytologist, 236(3), 797–799. https://doi.org/10.1111/nph.18377