MOVED TO TUES AUG 6, PS 19-23 // Soil parameters associated with the invasive nitrogen fixing shrub autumn olive (Elaeagnus umbellata)
Autumn olive (Elaeagnus umbellata) is an invasive nitrogen fixing plant commonly found throughout the U.S. Midwest region. The most common method for autumn olive removal is cutting, combined with herbicide application. We therefore predicted that autumn olive will have a significant legacy effect on soils after its removal. In 2012, we set up two permanent plots across two autumn olive populations in central Michigan. Soils samples were taken from a regular grid (5x5 m) that started in the autumn olive population and ended in an adjacent uninvaded area. Soil parameters (pH, organic matter, available ammonium and nitrate and P) were determined for all soil samples. Bacterial communities (overall, and ammonia oxidizer) were characterized using PCR-DGGE. Microbial function was determined by measuring five enzyme activities, as well as net rates of ammonia and nitrate production in soils. Soil variables were related to proximity to, and density of, autumn olive plants. In the fall of 2012, autumn olive plants were removed from half of the sample grid. We report here the baseline soil characteristics that will be used to determine the legacy effect of autumn olive in the upcoming years.
Contrary to what we expected, there was no association between nitrogen in the soil and autumn olive. In contrast, phosphorus in the soil was significantly correlated with autumn olive proximity (higher P concentrations in soils closer to autumn olive) and density (higher P concentrations found in denser autumn olive patches). Autumn olive was also associated with lower pH and organic matter in the soil. Several enzyme activities were significantly correlated with the proximity to autumn olive plants. Acid and alkaline phosphatases, beta-glucosidase and N-acetyl-glucosaminidase were all significantly lower in soil samples that were closer to autumn olive.