Immediate and Long-Term Effects of Invasive Plant Species on Soil Characteristics.

Research on invasive species has typically focused on characteristics of the organism in question.  Often these species are superior competitors with higher resource acquisition and/or more efficient resource utilization over native species.  Invasive species may alter soil characteristics or interact with the soil microbial community to yield a competitive advantage.  Our objectives were to determine: i) if invasive plant species alter soil physical, chemical or biological properties; and ii) the long-term effects of invasive plant species on soil properties and subsequent implications on ecological restoration efforts.  We focused on sericea lespedeza (Lespedeza cuneata ), a plant that may be allelopathic. Soil samples were collected from four locations in Central Missouri, USA:  an old-field with abundant sericea lespedeza, two restored sites, and a remnant prairie that has never been plowed.  The restored sites, planted in 2011 and 2013, were under similar management:  3-5 years of cropping (corn or soybean) to eradicate undesirable plants followed by broadcast seeding with seeds collected from near-by prairies to restore prairie assemblages.  At each site we collected four soil samples at two depths (0-5cm and 5-10cm).  Soils were intentionally collected underneath sericea lespedeza at the old field site, while at the other 3 sites sericea lespedeza was intentionally avoided. Soil was analyzed for : i) physical properties:  color, texture, bulk density and water-stable aggregates; ii) chemical properties: pH, base cations, active-C, total soluble phenolics, and electrical conductivity; and iii) biological properties: β-glucosidase and β-glucosaminidase for community function and PLFA for community structure.  Nearly every analysis differed significantly between the unplowed prairie reference site and the other three sites. The restored sites generally did not differ from the invaded old-field.  These results indicate that the restored prairies are not fully recovered.  Although above ground traits appear as prairie, soils still resemble that of an invaded site. These results indicate that more time may be needed before soil properties fully recover.  Additional investigations, including other sites in the region, are needed to verify this work.