The effect of an invasive shrub (autumn olive, Elaeagnus umbellata) on soil microbial communities depends on the proximity of soil to the invasive plant

Background/Question/Methods

Autumn olive is an invasive plant species that fixes nitrogen; therefore it is expected to alter soil microbial communities involved in nitrogen cycling.  In this study we determined the effect of autumn olive on the overall microbial function and the diversity of nitrifiers in soil.  Soil samples were collected at three different sites in a rectangular grid at the edge of an invaded area.   The location of all autumn olive plants in the grid was recorded. DNA from each sample was extracted and the diversity of nitrifiers was determined using PCR-DGGE using primers specific for bacterial and archaeal ammonia oxidizers, and nitrite oxidizers.  The overall function of soil microbial communities was assessed using phosphatase and phenol oxidase/peroxidase activity assays.  Microbial parameters were related to the local density of autumn olive and the proximity of autumn olive plants to soil samples.

Results/Conclusions

Soil samples that were closer to autumn olive appeared to have more altered microbial communities.  Differences were more prominent for certain parameters of the soil microbial community, for example, phosphatase activity.  Our results suggest that the effect of autumn olive on soils is heterogeneous and strongly dependent on the local density of the invasive plant.