Effects of Different Degrees of Xanthium spinosum Invasion on the Invasibility of Plant Communities in the Yili Grassland of Northwest China.

Simple Summary: The effects of invasive plants on species diversity and ecosystem stability differ owing to the different stages of invasion. Xanthium spinosum is an invasive weed that is widely distributed in Europe, Asia, and North America. Its adaptability and competitive advantage over native species have led to agricultural loss and biodiversity reduction, yet its impact on local plant communities under different degrees of invasion has not been reported. Therefore, in this study, we aimed to investigate the effects of different degrees of invasion by X. spinosum on the diversity, stability, and invasibility of local plant communities in Yining County, Xinjiang, China. We believe that our study makes a significant contribution to the literature because we found that as the degree of X. spinosum invasion increased, species diversity and community stability decreased, while community invasibility increased. Notably, a light degree of invasion was found to enhance the diversity and stability of local plant communities. Based on our findings, we recommend that X. spinosum be controlled and eradicated in the early stages of invasion to prevent further invasion and harm to indigenous species. Studying the effects of different degrees of exotic plant invasion on native plants' community structure and plant diversity is essential for evaluating the harm caused to ecosystems by plant invasion. In this study, we investigated the effects of Xanthium spinosum, a widespread invasive species, on plant community species diversity and community stability in the Ili River Valley area of Xinjiang, China, under three invasion levels (no invasion and low, moderate, and heavy invasion), and the competitive advantage index, invasion intensity, and contribution of plant community species diversity to community stability and invasibility were determined for the prickly fungus under different degrees of invasion. The results show that there were significant differences (p < 0.05) in the species diversity and community stability of plant communities caused by different degrees of invasion of X. spinosum. The species diversity and stability of plant communities were negatively correlated with the community invasibility, competitive advantage, and invasion intensity of X. spinosum (p < 0.05); therefore, the competitive advantage and invasion intensity of X. spinosum increase with the increase of its invasion degree. On the contrary, community species diversity and stability decreased with the increase of its invasion degree, ultimately leading to differences in community invasibility under different invasion degrees. The Shannon–Wiener and Simpson's indices were the greatest contributors to community stability and invasibility, respectively. Moderate and heavy levels of invasion by X. spinosum reduced the diversity and stability of local plant communities, increased the invasibility of communities, and substantially affected the structures of plant communities. Therefore, the continued invasion by X. spinosum will have an immeasurable impact on the fragile ecosystems and diversity of indigenous species in Xinjiang. We recommend that this invasive species be controlled and eradicated at the early stages of invasion to prevent further harm. [ABSTRACT FROM AUTHOR]