Invasive Amaranthus retroflexus obtains a competitive advantage over native A. tricolor under the addition of A. retroflexus leaf litter

There is a scarcity of research examining the influences of the addition of leaf litter from invasive plants on their own growth performance, particularly in the context of their own competitive advantage when co-cultured with native plants. This study aimed to examine the influences of the addition of a gradient of the invasive plant Amaranthus retroflexus L. leaf litter (ARLL) on its competitive advantage. An indoor planting experiment was conducted to analyze the competitive advantage of A. retroflexus with three forms of incubation conditions, that is, A. retroflexus in the monoculture, A. tricolor L. in the monoculture, and A. retroflexus co-cultured with A. tricolor. The addition of a low amount of ARLL was found to significantly enhance the competitive ability to obtain sunlight of both Amaranthus plants. The leaf photosynthetic capacity of A. tricolor and the growth competitiveness of A. retroflexus were found to be greater in the co-culture than in the monoculture. The competitive ability to obtain sunlight, the relative competitive intensity, and relative dominance of A. retroflexus were found to be stronger than those of A. tricolor regardless of the amount of ARLL and the form of incubation condition. Consequently, A. retroflexus can obtain a competitive advantage over A. tricolor under the addition of a gradient of ARLL. Accordingly, the stronger competitive advantage of A. retroflexus may facilitate its invasion process.