Comparison of the Allelopathic Potential of Non-Native and Native Species of Mediterranean Ecosystems

Allelopathy is a frequent interaction between species in Mediterranean ecosystems and it is also one of the proposed strategies to explain the colonisation of invasive species. To confirm the importance of allelopathic potential as a mechanism of invasion of non-native species in Mediterranean ecosystems, it would be advisable to compare the allelopathic effects of non-native plants with native plants on the same target species and thus avoid overestimating the role of phytotoxicity in the invasion process. The main objective of this work was to compare the allelopathic activity of native species typical of Mediterranean ecosystems, classified as allelopathic, with the allelopathic activity of non-native species that may have an invasive character in these ecosystems. To this end, we selected three native species (Cistus ladanifer, Pistacia lentiscus, and Pistacia terebithus) and three non-native species (Acacia dealbata, Acer negundo, and Salix babylonica), and we analysed their effect on the species Lactuca sativa and the native species Lavandula stoechas and Echium plantagineum. The tests on L. sativa showed that all species have allelopathic activity. The tests on L. stoechas and E. plantagineum revealed that P. terebinthus exerted the greatest effect, being the only species that maintained an inhibitory effect at extract concentrations of 50% and 25% in all the analysed parameters, except in germination and cotyledon emergence for E. plantagineum. There were no significant differences in the effect on germination between non-native and native species, although significant differences were found in the effect on root size in the three analysed concentrations, with the native species producing greater inhibition. In conclusion, these species exert a negative effect on the selected native target species, but the negative effect of the native species is greater than that of the non-native species. These results indicate that it is important to compare the allelopathic effects of invasive and native species to correctly estimate the phytotoxic effect of invasive species on their invasiveness.