Soil heterogeneity modulates competitive interactions between Solanum rostratum and replacement control plants

Background Plant replacement control is an important ecological approach for managing the invasive weed Solanum rostratum , yet its effectiveness is strongly mediated by soil conditions. However, current screening of replacement species often overlooks how soil heterogeneity alters competitive outcomes and plant–soil nutrient feedbacks, limiting the stability and general applicability of this approach. We conducted a two-factor pot experiment using soils collected from typical regions in China where S. rostratum is widely distributed. Monocultures and mixtures of S. rostratum and six native forage species were established. Plant biomass and chlorophyll content were measured, competitive effects were quantified using the log response ratio (lnRR), and redundancy analysis was used to link plant performance with soil nutrient dynamics. Results Mixed planting consistently suppressed S. rostratum across all soils (lnRR < 0), although the magnitude of suppression and the most effective replacement species varied markedly among soil types. Soil nutrient variation explained 30.69% of the variation in S. rostratum traits. Leymus chinensis and Festuca arundinacea showed greater competitiveness in soils with higher organic matter or nitrogen availability, whereas Medicago sativa and Agropyron cristatum exerted stronger suppression where plant performance was closely associated with changes in nutrient availability. Notably, M. sativa maintained relatively stable suppressive effects even under nutrient-poor conditions. Conclusion Our results demonstrate that replacement control efficacy is jointly regulated by species-specific competitive ability and soil nutrient feedbacks under heterogeneous soil conditions. These findings highlight the importance of matching replacement species to soil environments to achieve stable and effective ecological control of S. rostratum .