Range-expanding plant species develop species-specific belowground interactions

Root-feeding nematodes prefer native plants, thereby indirectly favoring congeneric range-expanding plant species
Range-expanding plant species may establish novel interactions with local soil organisms in their new range. However, the native soil community might not be adapted to root compounds produced by these new species. Therefore, interactions between range-expanders and native soil organisms might have different outcomes compared to similar interactions of related native plants. In turn, these altered interactions might influence the performance of the range-expanders. Here, we tested the hypotheses that 1) native root-feeding nematodes are more strongly attracted by native plants than by congeneric range-expanders, 2) root-feeding nematodes multiply better on native plants than on congeneric range-expanders and 3) in the presence of root-feeding nematodes, range-expanding plant species will have a competitive advantage over related natives. To examine nematode preference, we performed choice experiments with 2 native root-feeding nematode species, using 3 pairs of range-expanding plants and congeneric natives. Subsequently, we examined reproduction of the nematodes on these 6 plant species, and the effects of nematode preference on competition between native and range-expanding plants. Our results show that in most cases, root-feeding nematodes prefer native plants over congeneric range-expanders and that nematode multiplication rates were indeed higher on their preferred hosts. Furthermore, range-expanding plant species that compete with native congeners can benefit from the disproportional performance of root-feeding nematodes on native plants. We conclude that in new ranges, range-expanding plant species can benefit from naïve natural enemies as these favor native plants over range-expanders. These results can help explain the abundance of some range-expanding plant species in their new range.