Allelopathic Effects of Native Versus Invasive Plants on One Major Invader

Area of Science:

• Plant Ecology
• Invasive Species Biology
• Chemical Ecology

Background:

• Allelopathy involves chemical interactions between plants, affecting neighboring species.
• Native species' allelopathy can confer biotic resistance against invasive plants.
• Exotic species' allelochemicals may facilitate their establishment, a phenomenon known as invasional meltdown.

Purpose of the Study:

• To investigate the allelopathic effects of four plant species on the invasive target species *Ludwigia hexapetala*.
• To determine if allelochemicals from exotic or native species influence *L. hexapetala*'s growth and physiology.
• To assess the role of autoallelopathy in the invasiveness of *L. hexapetala*.

Main Methods:

• Two experiments were conducted using root and leaf leachates from *Ludwigia hexapetala*, *Ludwigia peploides*, *Myriophyllum aquaticum*, and *Mentha aquatica*.
• Target species *L. hexapetala* was exposed to these leachates, and its stem length, relative growth rate, and physiological traits (nitrogen balance, flavonol, chlorophyll, anthocyanin indices) were measured weekly.
• Aboveground and belowground biomass, lateral branch number, and length were determined at the experiment's conclusion.

Main Results:

• Root leachates of *L. peploides* and *M. aquaticum* stimulated flavonol synthesis in *L. hexapetala*.
• Leaf leachate of *L. hexapetala* also stimulated its own flavonol synthesis, indicating autoallelopathy.
• Root leachates from both *Ludwigia* species and leaf leachate from *M. aquaticum* promoted lateral branch production in *L. hexapetala*, with *L. peploides* root leachate also increasing total biomass.

Conclusions:

• The autoallelopathy of *L. hexapetala* may contribute to its invasive success.
• The invasive species *M. aquaticum* and *L. peploides* appear to facilitate the establishment of *L. hexapetala*, suggesting an 'invasional meltdown' scenario.
• *Mentha aquatica* leachates did not affect *L. hexapetala*, indicating no biotic resistance from this native species in the studied community.