Due to recent climate change, many plants and associated aboveground and belowground organisms expand their range to higher latitudes and altitudes. Because of different range expansion rates, co-evolved plant-soil interactions can become disrupted. In newly colonized areas, range-expanding plant species enter the local soil food web, thereby establishing new, often non-coevolved interactions. As native soil organisms might not be adapted to secondary root metabolites of the new plant species, interactions between range-expanders and native soil organisms might have different outcomes than with native plants. In turn, these altered interactions might influence the performance of the range-expanders. We studied interactions of root-feeding nematodes with range-expanding plant species and congeneric native plant species. A previous experiment showed that multi-trophic plant-microbe-nematode interactions are established differently in the rhizospheres of range-expanding plant species compared to related natives. Here, we tested the hypotheses that 1) native root-feeding nematodes are more strongly attracted to native plant species than to congeneric range-expanders, 2) root-feeding nematodes multiply better on native plant species 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. We examined nematode preference by performing choice experiments with 2 native root-feeding nematode species, using 3 pairs of range-expanding and congeneric native plant species. We also examined nematode reproduction on all 6 plant species, and studied competition between native and range-expanding plants with and without nematodes. To explain differences in nematode attraction, we also analyzed root metabolite composition of all 6 plant species.
Our results show that in two plant pairs the nematodes preferred the native plant species over the related-range expanders. Preference corresponded well with reproduction on natives vs range expanders. In one pair there was no consistent nematode preference, and nematode reproduction was slightly higher on the range-expander. The range-expanding plant species with the most novel root chemistry repelled nematodes, had lowest nematode reproduction, and highest performance in competition in the presence of root-feeding nematodes. The root chemistries of the other two range-expanders only slightly differed from the natives and both range-expanders did not gain a competitive benefit over the natives in the presence of nematodes. We conclude that in new ranges, range-expanding plant species can benefit from naïve natural enemies as these favor native plants over range-expanders, especially when the latter have strongly differing root chemistries. These results can help explain abundance of range-expanding plant species in their new range.