The Invasive Plant Amaranthus spinosus L. Exhibits a Stronger Resistance to Drought than the Native Plant A. tricolor L. under Co-Cultivation Conditions When Treated with Light Drought

Drought may facilitate the invasion process of invasive plants, mainly because invasive plants can obtain a stronger growth competitiveness than native plants under drought. It is therefore imperative to illuminate the mechanisms underlying the successful invasion of invasive plants under drought, with a particular focus on the differences in the resistance of invasive and native plants to drought. This study aimed to elucidate the differences in the resistance between the invasive plant <i>Amaranthus spinosus</i> L. and the native plant <i>A. tricolor</i> L. to drought under a gradient of drought. The resistance of co-cultivated <i>A. spinosus</i> to drought was significantly higher than that of co-cultivated <i>A. tricolor</i> under light drought. Hence, <i>A. spinosus</i> may obtain a stronger competitive advantage than <i>A. spinosus</i> under co-cultivation conditions when treated with light drought. The resistance of the two plants to drought may be predominantly influenced by their height and biomass. This present study also defines a method for evaluating the stress resistance of a given plant species to stress by calculating the stress resistance index. This present study offers a robust theoretical foundation for determining the stress resistance of a given plant species and the environmental management of <i>A. spinosus</i> under drought.