Invasive plants can regulate soil microbial communities to influence nutrient cycling and enhance their competitive advantage. However, the effects of invasive plants on rhizosphere soil bacterial community structure and nitrogen acquisition-related processes in the ecologically fragile karst rocky desertification regions remain unclear. In this study, metagenomic sequencing was used to examine how the degree of Chromolaena odorata invasion affects rhizosphere soil nitrogen-cycling bacterial communities and nitrogen cycling-related functional genes, with the aim of obtaining insights into potential shifts in rhizosphere nitrogen cycling functions associated with plant nitrogen acquisition. Soil inorganic nitrogen shifted from NH4+ dominance under mild invasion to NO3- dominance under heavy invasion. Bacterial community composition differed significantly across invasion degrees, with enrichment of taxa associated with nitrogen cycling. The relative abundance of nitrogen-cycling functional genes also varied with the invasion degree: assimilatory and dissimilatory nitrate reduction genes were enriched under mild invasion, whereas nitrification genes were more abundant under heavy invasion. These findings suggest invasion-degree-dependent shifts in nitrogen acquisition, potentially mediated by rhizosphere soil bacteria and nitrogen-cycling-associated functional genes. Structural equation modeling supported indirect effects of invasion degree on soil inorganic N via pH-mediated microbial changes. This study clarifies how C. odorata invasion reshapes rhizosphere soil nitrogen-cycling bacteria and functional genes in karst ecosystems, improving our understanding of the impact of invasive plants on soil nitrogen cycling. Our findings provide a scientific basis for ecological restoration and invasive plant management in karst regions.