Background and Aims: Soil abiotic and biotic properties shaped by plants impact future plant invasions (“plant-soil feedbacks”). Human activities have increased soil heavy metal concentrations, often where invasion pressure is increasing, so it is imperative to investigate plant-soil feedback mechanisms associated with invasive species in environments contaminated by heavy metals. Methods: We experimentally created soils with different Cd concentrations and conditioned them with invasive Phytolacca americana or native Phytolacca acinosa (or without plants) in a greenhouse experiment. We measured soil chemical, microbial (by PFLAs), and physical properties. We grew individual plants of P. Americana or P. Acinosa in these soils in a feedback phase. Results: Soil Cd increased invasive mass but decreased native mass. Fungi and bacteria were abundant in invasive conditioned soils, especially without Cd. Phenol, flavonoid and tannin concentrations and soil pH increased with Cd when plants were present. Phenol and tannin concentrations were higher with invasive plants but flavonoids were lower. In the feedback phase, invasive mass was sensitive to soil microbes. Native plants were smaller in invasive (away) soils, especially with higher soil Cd concentrations, reflecting their sensitivity to soil chemicals and soil physical characteristics. Conclusion: These results indicate that P. Americana invasions are enhanced both through direct effects of soil Cd on P. Acinosa as well as through Cd magnifying the negative effects of soil chemical and physical characteristics on the native. This study offers valuable insights into the influence of PSF on plant invasion processes in the context of soil heavy metal pollution.

Increasing evidence suggests that invasive plants can sustain high growth rates in heavy metal-enriched environments, while native species do not contribute to their invasion success. However, the underlying mechanisms are poorly understood. This study examined the invasive plant Phytolacca americana and native Phytolacca acinosa in Cd-contaminated soils in China. The results showed that, while native plant biomass decreased at higher soil Cd concentrations, invasive plant biomass remained unaffected. Soil enzyme activities decreased with increasing Cd concentration but were higher in soils where invasive plants grew than those in soils where native plants grew. Phytolacca americana accumulated more Cd, particularly in the leaves and under higher soil Cd concentrations. Native seed germination was inhibited with increasing litter-Cd concentration, whereas invasive seed germination was unaffected. These findings suggest that the ability of the invasive species to mitigate the negative effects of Cd pollution on soil enzyme activities contributed to their higher Cd-tolerance by maintaining soil nutrient availability. Additionally, higher leaf-Cd levels in invasive plants constitute an elemental defence. Overall, heavy metal pollution not only favoured invasive plants by suppressing native plant growth but may have also promoted invasion through the effects of Cd accumulation in invasive litter on native seed germination.

Studies on the effects of invasive plants on native herbivores often only concern about short-term effects, and few studies have focused on the long-term effects of invasive plants on herbivores. We investigated the development of Spodoptera litura to the second generation on the invasive plant Phytolacca americana and the exotic non-invasive plant Phytolacca icosandra, meanwhile, we tested the impacts of the P. americana on the S. litura through laboratory bioassay, oviposition preference and detoxifying enzyme activity analysis. The results show that S. litura have feeding and oviposition preference to P. icosandra, the larval weight and oviposition preference index (OPI) of S. litura feeding on P. icosandra are higher. However, the developmental duration of S. litura on P. icosandra is shorter than that of P. americana; the activities of Acetyl cholinesterase (AchE) and Glutathione-S-transferase (GST) of S. litura feeding on the leaves of the P. americana were higher than those of feeding on artificial diet and P. icosandra. There is no significant difference of activities of AchE and GST between S. litura feeding on artificial diet and P. icosandra. These findings have important implications for the evaluation of the impacts of invasive plant P. americana on native herbivores in the local ecosystem and explain that invasive plant has higher resistance to herbivores and suffer less damage than exotic non-invasive plant in the invaded range.