Allelopathic potential of invasive species is determined by plant and soil community context

摘要

The search for mechanisms to explain the competitive dominance of invasive species has generated much interest in testing for allelopathy as a major mechanism of plant invasion. The Novel Weapons Hypothesis postulates that invasive plants disproportionally impact native plants by producing novel allelochemicals. We studied the allelopathic potential of three invasive and three native species on twelve co-occurring plant species in the Eastern Deciduous Forest of Indiana, USA, using foliar leachate and soil with an intact microbial community. Our bioassay was a full factorial test of two soil treatments and six foliar leachates on the germination and growth of 12 species (2 x 6 x 12 full factorial). The strength of allelopathic impacts were context dependent, with significant 3-way and 2-way interactions between leachate species, target species, and soil microbial communities (live vs. sterilized). Allelopathic potential was different between life stages of the target species. Ligustrum vulgare's and Lonicera maackii's impacts on some native species supported the Novel Weapons Hypothesis; however, the invasives as a group did not significantly affect growth and had a weaker effect on germination than the effect of certain invasive species individually. For example, native Cercis canadensis reduced germination and growth in some conditions. Our results in the live soil treatment indicate that some natives, such as Elymus hystrix, should be resistant to Lonicera maackii and Ligustrum vulgare, but these shrubs' allelopathy could contribute to the decline of susceptible native species.