Invasional meltdown in plants: The reduction of litter allelochemical promoted positive alien biotic interactions

One core focus of ecology is how the differences in community invasion resistance are established. An invasional meltdown suggests that the establishment of one alien invader might promote further invasions through soil microbes. However, whether a similar effect might be mediated by plant litter and whether such a situation might depend on environmental factors condition is still poorly understood. We grew Phytolacca americana as target plants in pot-mesocosms under two interaction species origin (alien vs native). In each species origin, we produced 36 combinations of two litter treatments, two soil microbe treatments, three soil phosphorus levels, and three P. americana density treatments. We found that although microbial communities differed by species origin, microbial inoculation had no effect on P. americana growth. Litter origin did affect plant performance;P. americana growth was greater under alien litter treatment. This phenomenon may come from the reduction in allelochemical (e.g., total phenolics) rather than nutrients, and these processes were significantly affected by P. americana density but not by soil phosphorus content.

Synthesis: Our study provides novel insights into the invasion process showing that biotic interactions between alien plants may mediate the invasional meltdown process through the action of litter. The main result highlights the importance of bio-control in areas invaded by multiple alien species.