Climate warming and anthropogenic activities have led to an increase in the prevalence of non-native plants in mountainous regions that previously exhibited limited occurrences. This phenomenon has resulted in detrimental effects on endemic plants and ecosystem functions. However, the variation in traits of non-native plants that successfully spread to high elevations, as well as the underlying drivers of these changes, remains poorly understood. In this study, we use Erigeron annuus, a cosmopolitan non-native plant that has invaded high elevations, as our model to explore its individual biomass pattern along a 1900 m elevation gradient. We also contrast this pattern with that of the native Artemisia lavandulifolia, which has the same distribution range as E. annuus. We found that the biomass of E. annuus displayed a hump-shape pattern along elevation, while the biomass of the native A. lavandulifolia gradually decreased with increasing elevation. By evaluating the effects of climate variables, soil properties, rhizosphere fungal communities, and their spatial mid-domain effect (i.e., geographic limitation) on plant biomass, we found that the biomass of E. annuus was primarily influenced by the spatial mid-domain effect, while the biomass of A. lavandulifolia resulted from a complex interplay of climatic variables and rhizosphere microbial communities. Our findings emphasize the importance of a spatial mid-domain effect on the growth of non-native E. annuus across elevation, indicating that the impact of E. annuus is probably greatest at mid-elevations and thus, where management priority should be set. Further investigations considering more non-native plant species and species’ traits will allow us to scrutinize this vision.