# Can allelopathic potentialities of Mediterranean plant species reduce the spread of invasive plant species, Acacia dealbata and Ailanthus altissima?

## TL;DR

This study shows that extracts from three Mediterranean plants can slow the growth of invasive species, but soil amendments reduce this effect.

## Contribution

The study demonstrates the allelopathic potential of three native Mediterranean species against two invasive plants and how soil amendments affect this.

## Key findings

- Leaf extracts from Cistus ladanifer, Cistus albidus, and Cotinus coggygria delayed germination and reduced seedling growth of Acacia dealbata and Ailanthus altissima.
- Higher doses of the extracts increased allelopathic effects, but compost addition reduced or canceled these effects.
- Allelochemicals from native plants could be a nature-based solution to manage invasive species along railway borders.

## Abstract

Beyond ecological and health impacts, invasive alien plant species can generate indirect and direct costs, notably through reduced agricultural yields, restoration, and management of the invaded environment. Acacia dealbata and Ailanthus altissima are invasive plant species that cause particularly significant damage to the railway network in the Mediterranean area. The allelopathic properties of Mediterranean plant species could be used as nature‐based solutions to slow down the spread of such invasive plant species along railway borders. In this context, a mesocosm experiment was set‐up: (i) to test the potential allelopathic effects of Cistus ladanifer, Cistus albidus, and Cotinus coggygria leaf aqueous extracts on seed germination and seedling growth of A. dealbata and A. altissima; (ii) to evaluate whether these effects depend on the extract dose; and finally, (iii) to estimate whether these effects are modified by soil amendment. Leaf aqueous extracts of the three native plant species showed negative effects on both seed germination and seedling growth of the two invasive species. Our results show that the presence of allelochemicals induces a delay in seed germination (e.g., A. dealbata germination lasted up to 269% longer in the presence of high‐dose leaf aqueous extracts of C. coggygria), which can lead to a decrease in individual recruitment. They also highlight a decrease in seedling growth (e.g., high‐dose C. coggygria leaf aqueous extracts induced a 26% decrease in A. dealbata radicle growth), which can alter the competitiveness of invasive species for resource access. Our results also highlight that compost addition limits the inhibitory effect of native Mediterranean plants on the germination of invasive alien plants, suggesting that soil organic matter content can counteract allelopathic effects on invasive alien plants. Thus, our findings revealed that the allelopathic potential of certain Mediterranean plant species could be a useful tool to manage invasive plant species.

In this study, we provide clear evidence that the leaf aqueous extracts of three Mediterranean native species (Cistus albidus, Cistus ladanifer and Cotinus coggygria) exhibit negative allelopathic effects on seed germination and seedling growth of the two invasive plant species (Acacia dealbata and Ailanthus altissima). These allelopathic effects increased with dose extract but are greatly reduced and even canceled in the presence of soil amendment.