Plant-soil interactions in the native range of two congeneric species with contrasting invasive success

The aim of this study was to compare plant-soil interactions in the native range of two congeneric European species differing in their invasive success in the world: a globally invasive Cirsium vulgare and non-invasive C. oleraceum. We assessed changes in soil nutrients and soil biota following soil conditioning by each species and compared performance of plants grown in self-conditioned and unconditioned soil, from which all, some or no biota was excluded. The invasive species depleted more nutrients than the non-invasive species and coped better with altered nutrient levels. The invasive species had higher seedling establishment which benefited from the presence of unconditioned biota transferred by soil filtrate. Biomass of both species increased in soil with self-conditioned soil filtrate and decreased in soil with self-conditioned whole-soil inoculum compared to unconditioned filtrate and inoculum. However, the increase was smaller and the decrease greater for the invasive species. The invasive species allocated less biomass to roots when associated with harmful biota, reducing negative effects of the biota on its performance. The results show that in the native range the invasive species is more limited by self-conditioned pathogens and benefits more from unconditioned mutualists and thus may benefit more from loss of effectively specialized soil biota in a secondary range. Our study highlights the utility of detailed plant-soil feedback research in species native range for understanding factors regulating species performance in their native range and pinpointing the types of biota involved in their regulation.