Effects of different types of heavy metal pollution on functional traits of invasive redroot pigweed and native red amaranth.
The differences in functional traits between invasive plant species (invaders hereafter) and natives are believed to be closely associated with whether the former are successful invasion. Meanwhile, variability in the type of heavy metal pollution can alter the growth and physiological performance of invaders. Thus, determination of the potential effects of different types of heavy metal pollution on functional traits of invaders is vital for illuminating the mechanisms supporting the success of invaders. This study aims to address the effects of the separated treatment of Cu, Cd, and the combined treatments of Cu and Cd on functional traits of invasive redroot pigweed (Amaranthus retroflexus L.; pigweed hereafter) and native red amaranth (A. tricolor L.; amaranth hereafter). Pigweed was significantly taller than amaranth under most treatments. The greater height of pigweed may award greater competitive ability for resource acquisition (particularly sunlight). Leaf shape index of pigweed was significantly larger than that of amaranth under all treatments. The larger leaf shape index of pigweed can enhance the efficiency of resource capture (especially sunlight capture) via adjustments to leaf shape and size. Hence, the higher height and leaf shape index of pigweed may facilitate its further invasion process. Heavy metal pollution (especially Cd) poses significant adverse effects on the growth and physiological performance of the two Amaranthus species. This may be because heavy metal pollution, especially Cd, can mediate toxicity on plant species. The combined treatments of Cu and Cd can confer an antagonistic effect on functional traits of the two Amaranthus species compared with the separated treatment of Cu or Cd. The main reason may be the fact that Cd and Cu influence each other's uptake for plants.