Recruitment limitation by the invasive shrub Mimosa pigra across multiple exposure pathways: evidence for a contributory allelopathic role

Early recruitment is a critical bottleneck in plant invasion because suppression at this stage can strongly reduce resident regeneration and reinforce invader dominance. Mimosa pigra forms dense stands in wetland and riparian habitats, yet the contribution of leaf-derived chemistry to its invasion success remains insufficiently resolved. We tested whether leaf extracts of M. pigra suppress recruitment-related traits across three recipient species and whether the resulting pattern is consistent with chemically mediated interference. Using concentration-gradient bioassays combined with physicochemical controls, four-parameter logistic modelling, activated carbon neutralization, litter-leachate assays, invaded-soil comparisons, and phytochemical profiling, we found strong concentration-dependent reductions in germination, seed vigor, root growth, shoot growth, and biomass accumulation. Root growth was consistently the most sensitive endpoint across species. Activated carbon partly alleviated inhibitory effects, while litter leachates and invaded soils also reduced establishment-related traits. These inhibitory responses were associated with a phenolic- and flavonoid-rich extract profile. Together, the findings indicate that M. pigra can limit early recruitment through multiple plausible exposure pathways and support a contributory, rather than exclusive, allelopathic role in the persistence of invaded stands.