The Effect of Native Plant Diversity on the Success of Invasive Species in Polluted Soils

Soil pollution can significantly disrupt native plant communities by weakening native species and giving invasive species a competitive advantage. This study aimed to assess the resistance of native species to invasive species in plant communities with varying species densities, focusing on growth traits and soil properties under the influence of different soil pollutants. Four native experimental communities varying in number of species were established, with each community paired with a distinct invasive species., i.e., C1 (four natives, i.e., Lactuca indica L., Plantago asiatica L., Leonurus japonicus Houtt., Alternanthera sessilis L. + Symphyotrichum subulatum (Michx.) G. L.), C2 (four natives, i.e., L. indica, P. asiatica, L. japonicus, A. sessilis + Sphagneticola trilobata L.), C3 (five natives, i.e., L. indica, P. asiatica, L. japonicus, A. sessilis, Hemistepta lyrata (Bunge) + S. subulatum), C4 (five natives, i.e., L. indica, P. asiatica, L. japonicus, A. sessilis, H. lyrata + S. trilobata). These communities were exposed to four soil pollutant treatments: (i) no pollutants (CK), (ii) PE microplastic particles (MP), (iii) cadmium, representing a heavy metal (HM), and (iv) both MP + HM. An ANOVA showed that MP, HM, and MP + HM significantly affected the biomass of both native and invasive species across all four communities (P < 0.05). Furthermore, microbial biomass carbon, nitrogen, and CO₂ emissions were higher in C2 and C4 soils (invaded by S. trilobata) than in C1 and C3 soils (invaded by S. subulatum). The invasion resistance index (IRIN) of the native species increased in C1 compared to C2 by 74.50, 49.86, 18.34, and 24.72% under CK, MP, HM, and MP + HM treatments, respectively. Similarly, the IRIN in C3 increased relative to C4 by 48.30, 30.45, 22.56, and 31.03% under the same treatments. The study concludes that invasion resistance of native species depends on species diversity, the specific invasive competitor, and the type of pollutant.