Competition mediates mycorrhizal dependency shifts for a species in its introduced and native range

Background/Question/Methods: The interactions between plant and soil mutualists, arbuscular mycorrhizal (AM) fungi in particular, may play a decisive role in influencing the establishment and the range expansion of exotic plants in new environments. However, whether there are post-introduction shifts in dependence on AM fungi and whether the dependency can be altered by competition remain poorly understood. We conducted a common garden experiment in order to test how native (US) and invasive (China) populations of an invasive plant Plantago virginica L. respond to AM fungi, and whether these responses are mediated by competition.

Results/Conclusions: We found that AM fungi increased the growth, reproduction, and plant P contents of the native populations, both with and without competition. However, the invasive populations benefited less from AM fungi compared to the native populations, demonstrating weaker mycorrhizal dependence. Invasive populations even exhibited reduced growth with AM fungi when grown with a native competitor. The different responses of the invasive and native populations to AM fungi indicate that different populations of P. virginica have differential strategies to better cope with the altered resources availability and competition pressure. These results suggest that adaptive alteration in mycorrhizal dependency in P. virginica may have occurred during its invasion. Although little is known about the factors driving these adaptations, the role of native competitors should be taken into account in future studies.