Invasive exotic plants are a major ecological problem and can cost millions of dollars a year per species in restoration efforts. Soils usually take thousands of years to develop, therefore, the long term effects these plants can have on soil properties within a relatively short period of time pose serious issues with remediation. Invasive woody plants are different from herbaceous plants because woody roots are concentrated in an area around the plant, and gaps are found between the roots of neighboring plants. The effects of woody invasive plants on soils may also strongly depend on the invasion context (open field, forest edge, interior forest). We present a study on the influence of the woody exotic plant autumn olive (Elaeagnus umbellata, L.) on soils in two different invasion contexts: an open field and a forest interior. Soil samples were collected immediately below autumn olive plant roots and from adjacent sites that had not yet been invaded (controls). Available nitrate and ammonium in soils were measured using 2M KCl extraction. Bacterial community composition was determined using denaturing gradient gel electrophoresis (16S rRNA gene).

Results/Conclusions

All soil samples had very low amounts of available nitrate (less than 1 μg/g dry soil), while ammonium ranged from 40-170 μg/g dry soil. Autumn olive invasion was associated with higher levels of nitrate in the open field, however, no difference was observed in the forest interior. In contrast, higher levels of ammonium were measured under autumn olive only in the forest interior. Autumn olive significantly affected the bacterial community in soils. Interestingly, the effect on bacterial communities also depended on the context of the invasion. In the open field soils, bacterial communities varied widely in control sites, but were very similar under autumn olive, indicating that the invasive plant has enriched certain bacteria in soil. In contrast, control sites in the forest interior had a uniform bacterial community. Autumn olive invasion altered those communities, however, the change was not consistent between different autumn olive samples. Our results clearly indicate that autumn olive is altering the structure and function of microbial communities in the soil. It appears that the effect is context specific, which should be taken into account during restoration efforts.