1. Division of Biological Sciences, The University of Montana, Missoula, Montana 59812, USA

Correspondence to: Ragan M. Callaway Correspondence and requests for materials should be addressed to R.M.C. (Email: ray.callaway@mso.umt.edu).

Abstract

Invasive plants are an economic problem and a threat to the conservation of natural systems. Escape from natural enemies might contribute to successful invasion¹, with most work emphasizing the role of insect herbivores^{2, 3, 4}; however, microbial pathogens are attracting increased attention⁵. Soil biota in some invaded ecosystems may promote 'exotic' invasion^{6, 7, 8, 9}, and plant–soil feedback processes are also important. Thus, relatively rare species native to North America consistently demonstrate negative feedbacks with soil microbes that promote biological diversity¹⁰, whereas abundant exotic and native species demonstrate positive feedbacks that reduce biological diversity¹⁰. Here we report that soil microbes from the home range of the invasive exotic plant Centaurea maculosa L. have stronger inhibitory effects on its growth than soil microbes from where the weed has invaded in North America. Centaurea and soil microbes participate in different plant–soil feedback processes at home compared with outside Centaurea's home range. In native European soils, Centaurea cultivates soil biota with increasingly negative effects on the weed's growth, possibly leading to its control. But in soils from North America, Centaurea cultivates soil biota with increasingly positive effects on itself, which may contribute to the success of this exotic species in North America.

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