A native herbaceous community exerts a strong allelopathic effect on the woody range-expander Betula fruticosa

Biological invasions by range-expanding native and alien plant species often reduce native plant community diversity and productivity. Superior performance of some invasive plants over native plants is due to production of allelochemicals by invaders that suppress growth of native plants. Nevertheless, native plants can also produce allelopathic compounds, which may provide biotic resistance against invasive plant species, in accordance with the homeland security hypothesis. In support of the hypothesis, several previous studies found evidence for allelopathic effects of native plant species on alien plant species. However, as most of these studies tested allelopathic effects of single native plant species on invasive plant species, the contribution of allelopathy to the resistance of native plant communities to invasion has received considerably less attention. Here, we performed two competition experiments in a greenhouse to test for potential pairwise allelopathic effects on each other of a woody range-expander Betula fruticosa and a community of four native herbaceous species in China. We tested whether B. fruticosa and the herbaceous community differed in their competitive effects and responses, and whether these were changed by the presence of activated carbon - an allelopathy neutralizer in the soil. Results show that presence of activated carbon ameliorated suppressive effects of the resident herbaceous community on above-ground biomass of B. fruticosa. By contrast, presence of activated carbon tended to aggravate suppressive effects of B. fruticosa on the resident herbaceous community. Overall, these results provide support to the homeland security hypothesis and suggest that strong biotic resistance of the resident herbaceous community may limit invasion success of the woody range-expander B. fruticosa.