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.