The influence of warming and biotic interactions on the potential for range expansion of native and nonnative species
Nonnative species are expected to be better range expanders than natives because plant-soil feedbacks are likely to be less negative for nonnatives owing to a lack of coevolved native soil pathogens. To test this hypothesis, we assessed whether plant-soil feedback affected performance of two natives and one exotic congener when subjected to climate conditions outside their current range, as predicted by distribution models. We grew seeds of the invasive species, Eugenia uniflora, and the common native species, E. foetida and E. axillaris, in pots in growth chambers that simulated environmental conditions for current (2010) and future (2060) spring temperature and light conditions of the projected new range. Soil biota were added to sterile potting soils in the form of fresh field-collected soil. We added the same amount of sterilized field-collected soil for controls. We tested for the effects of soil biota from different sites by collecting soils from the current range (south and central Florida) and within the projected new range (north Florida). For each species, we performed a three-way analysis of variance test to determine the relationship between mean strength of plant-soil feedbacks with soil treatment, site, and warming treatments as main effects.
In direct contrast to our hypothesis, soil feedback for the non-native plant species was more strongly negative compared to both natives, but this was unaffected by altered climate conditions. Soil origin (north, central, and south FL) had no effect on shoot biomass for all three species. Shoot biomass of the natives Eugenia foetida and E. axillaris was not affected by site, climate, soil biota treatment, or combinations of these factors. The nonnative Eugenia uniflora shoot biomass was strongly negatively affected by the soil microbiota, however it was not affected by the warmer temperatures or the different sites from which the soil was gathered. Thus, biomass of this nonnative species was not affected by a 1° C difference in temperature or the composition of the soil biota from disparate biogeographic regions. The strong negative effect of soil biota on the nonnative species but not on the native species suggests that the soil microbiota in natural systems exerts strong resistance to invasion by nonnative species. However, plant-soil feedback between the soil biota to and this high impact invasive species was not affected by warming temperatures as we had hypothesized.