Soil origin influences the potential for plant-soil feedbacks to facilitate plant invasion
Most plant species are thought to generate negative plant-soil feedbacks (PSF) wherein they perform poorly in soil that was previously occupied by conspecifics. However, some species generate positive PSF in which they perform better in soil previously occupied by conspecifics than in other soil; some of these PSF preferentially benefit conspecifics. This leads to the Plant-Soil Feedback Hypothesis of Invasion which states that plant species may have greater invasive potential when they generate PSF types that preferentially benefit conspecifics. If an invasive plant benefits from PSF then: (1) the PSF should a type that preferentially benefits conspecifics (conspecific positive feedback or heterospecific negative feedback); and (2) the PSF should be consistent among invaded sites. The objective of this study was to examine PSF as a trait that confers invasive potential to four plant species. To address this objective, three soil types were collected from distinct areas within and outside the range of each invader and transported to a glasshouse. In the glasshouse, a two-stage experiment was run and the effects of soil conditioning by the invasive species on conspecific and heterospecific performance was evaluated. Invasive species used were Agropyron cristatum, Centaurea solstitialis, Poa pratensis, and Taeniatherum caput-medusae.
Support for the Plant-Soil Feedback Hypothesis of Invasion was found for two of the four invasive species. T. caput-medusae created an invasive PSF in all of three soils and A. cristatum created an invasive PSF in two of the three soils. However, P. pratensis did not create PSFs and C. solstitialis only created a PSF in the soil from outside its invasive range. These results suggest that PSF generation may contribute to the success of T. caput-medusae and A. cristatum, but not to P. pratensis and C. solstitialis.
The limited support we found for the Plant-Soil Feedback Hypothesis of Invasion does not signify weakness of the hypothesis, but instead lends support to the idea that most likely a number of traits exist that confer invasive potential (such as competitive ability, phenotypic plasticity, or PSF generation) and a successful invader may need only possess one.