The relative importance of immediate allelopathy and allelopathic legacy in invasive plant species

Some introduced invasive species may be competitively superior to natives because they release allelochemicals, which egatively affect native species. Allelochemicals can be immediately effective after being released but can also persist in soils, esulting in a legacy effect. However, to our knowledge there are no studies which distinguish between allelopathic legacy and mmediate allelopathy of invasive species and also test for their relative importance and possible interdependence. We used eleven invasive species and tested whether they show immediate allelopathy and allelopathic legacy effects in a actorial pairwise competition experiment using field-collected soil (invaded/non-invaded) and activated carbon to neutralize llelochemicals. We grew two native and the invasive species in both monocultures and pairwise mixtures. In monocultures, the native species did not experience an allelopathic legacy effect of the invasives, suggesting that invaders enerally lack persistent allelochemicals. However, the effects of invader allelochemicals were modulated by competitive nteractions. In competition, immediate allelopathy decreased competitive ability of natives, while allelopathic legacy positively ffected the natives. Moreover, immediate allelopathic and allelopathic legacy effects were strongly negatively correlated. Our results suggest that both immediately released allelochemicals and the allelochemical legacy of invasive species are mportant for plant performance under natural conditions, and that natives should be able to recover once the invaders are emoved. To test whether immediate allelopathy is responsible for plant invasion success, further studies should compare llelopathic effects between invasive and closely related native species.