Soil microbial community structure of range-expanding plant species differs from co-occurring natives

1. Due to global warming and other changes in the environment, many native and exotic plant species show range expansion from lower to higher latitudes. In the new range, the (in)ability of range-expanding plants to establish associations with local soil microbes can have important consequences for plant abundance; however, very little information exists on rhizosphere communities of range-expanding plant species. Here, we examine the rhizosphere microbial community composition of range-expanding plant species in comparison with phylogenetically related species that are native in the invaded range. 2. We tested the hypothesis that range-expanding plants species would promote fewer shifts in rhizosphere communities than congeneric natives would. In order to test this, soil was collected from the invaded habitat and six range-expanding and nine congeneric natives were planted individually in pots to condition soil microbial communities. 3. After harvesting, individuals of the same species were planted in conditioned own and control soils to test the legacy effects of soil conditioning on biomass production. The control soils were mixtures of soils conditioned by all other plant species, except congenerics. After 10 weeks of plant growth, we determined the rhizosphere community composition of bacteria, fungi, arbuscular mycorrhizal fungi (AMF) and Fusarium spp. 4. All groups of microbes were analysed qualitatively using denaturating gradient gel electrophoresis (DGGE). Ergosterol was determined as a quantitative measure of nonarbuscular mycorrhizal fungal biomass, and real-time PCR was applied to detect amounts of Fusarium spp. 5. Range-expanding plants had less fungal hyphal biomass and lower amounts of Fusarium spp. in the rhizosphere than congenerics. Bacterial community composition was influenced by a combination of soil conditioning and plant origin, whereas fungal communities, AMF and Fusarium spp. were less pronounced in their responses to the experimental treatments. 6. Synthesis. We conclude that the lack of legacy effects in range-expanding plant species compared with natives may be due to differences in bacterial rhizosphere community composition, or to different quantities of potential pathogenic fungi. If the range-expanding plant species were benefiting more from AMF, effects will not have been due to differences in community composition, but we cannot exclude other options, such as different effectiveness of AMF or other soil biota in the rhizosphere of range-expanding vs. native plant species. The greater accumulation of bacterial and fungal pathogens in the rhizosphere of natives in relation to range expanders might explain the successful establishment of range-expanding plants