Plants undergoing climate change induced range expansion may become decoupled from their current associated soil microbial community due to differences in range expansion ability. This would allow for increased success in novel soil microbial communities for plants typically experiencing negative plant-soil feedbacks. Plant-soil feedback studies tend to show negative feedbacks, but our knowledge of how these feedbacks will impact range expansion ability is limited. Using a greenhouse plant-soil feedback experiment with a total of 6 plant species spanning an elevational gradient of subalpine to alpine zones, we tested the growth of each lower elevation species in their own soil and in the soil microbial community of the higher elevation species with and without a higher elevation plant.
Our hypotheses were as follows: 1) plants will be more successful with soil microbes from the higher elevation species than with their own soil microbes and 2) the presence of interspecific competition from the resident species will cause the range expander to experience a more negative feedback. Above and belowground biomass and seedling mortality was measured after 3 months of growth.
Consistent with our predictions, plants tended to be less successful in their own soil microbial community than in either sterilized control soil or soil inoculated with microbes from higher elevation species. The strength of the negative feedbacks in their own soil was slightly greater for low elevation species than high elevation species. We found that aboveground competition had a substantial effect on growth and interacted with the soil microbe treatment. Competitor identity was important, but there were no clear trends with respect to elevation. Our results suggest that escape from negative plant-soil feedbacks may be an important mechanism leading to the success of plants undergoing upslope range expansion. Taking into account plant-plant interactions, low elevation species experiencing negative plant-soil feedbacks may be able to colonize higher elevation environments at a rate faster than what is predicted by niche models based on climate alone.