Ailanthus altissima (tree of heaven) is a widely distributed invasive species which can outcompete native species for space and light, and affect soil properties and nutrient availability. Ecological genetics studies of invasive species focus on differences between such species in native and introduced ranges, but to date, have neglected varying population-level adaptive strategies. We hypothesized that there are beneficial plant-soil feedbacks that allow introduced populations to spread in their different environments. Furthermore, we hypothesized that seeds from each population would germinate and perform best in their own soil. We collected seeds and soils from three populations of A. altissima in the eastern U.S. and reciprocally planted the seeds from 25 seedling families (10 from PA, 5 from VA, and 10 from TN) in each of the soil types (field soil), as well as in soil that had been sterilized with gamma irradiation. Soil sterilization allowed us to identify biotic vs. abiotic determinants of feedbacks. We measured rates of seedling germination and performance measures such as stem height and number of leaves.

Results/Conclusions

We found that seedling germination rates were significantly affected by soil type in field (p=0.01) but not sterile (p=0.28) soils, with the highest germination rates in the Pennsylvania field soil. Measures of seedling performance at the peak of growth show that stem height and number of leaves are significantly different by soil and seed population (p<0.05), with all seedllings grown in Virginia field soils outperforming seedlings grown in other soils and all Virginia seedlings outperforming seedlings from other populations in all field soils. We attribute these patterns to the effects of the soil biota, as plant performance was 20-70% lower in sterile soils  and population variation patterns were absent in the sterile soil with the exception of an effect of soil type on stem height (p<0.0001). Our results suggest that not only is there genetic variation in performance of invaders, but that variation in soils due to soil biota can affect the establishment and performance of Ailanthus altissima seedlings, supporting the hypothesis of the importance of  plant-soil feedbacks to the persistence of invasive species.