Environments experienced by parental plants may potentially influence the performance of their offspring. These effects may also vary depending on the current environment experienced by the offspring. However, whether these transgenerational effects, especially those induced by biotic factors such as competition, can persist for multiple generations has not been tested. Here, we examined intraspecific competition‐induced transgenerational effects across multiple generations using a floating clonal plant Spirodela polyrhiza, by growing three successive generations each under either low or high density. The second‐generation offspring performed better when the first‐generation plants were grown under low than under high density, independently of the density experienced by the second generation. The third‐generation offspring performed better under low than under high density, and the difference was more pronounced when the second‐generation plants were grown under low density. Moreover, the density of the first and second generation interacted to influence the morphology of the third‐generation offspring. These results indicate that competition‐induced transgenerational effects in S. polyrhiza can vary depending on the competition environment of its offspring and that these effects can persist across multiple generations.

Many studies have shown that increasing species diversity generally increases ecosystem functioning, but few have evaluated the role of species diversity in soil pollutant removal, especially for organic pollutants. We test the hypothesis that increasing plant diversity can enhance soil pollutant removal. To test the hypothesis, we conducted two experiments: one for removal of cadmium and the other for removal of cypermethrin from the soil. In both experiments, plants were grown in monocultures, four‐ and eight‐species mixtures in soils contaminated with the pollutants. Contaminated soils without plants were also included as controls. Our results showed that the efficiency of cadmium removal from the soil decreased with increasing plant species richness. The negative effect of diversity on cadmium removal was largely attributed to species underyielding in plant mixtures. In contrast, the efficiency of cypermethrin removal from soils increased with increasing plant species richness. The positive effect of diversity on cypermethrin removal was likely due to the presence of Taraxacum mongolicum which had the lowest biomass but the highest removal efficiency. Our results suggest that species diversity may regulate pollutant remediation, and this is pollutant‐dependent. Moreover, the performance of individual species can strongly influence the direction and magnitude of the diversity effect on soil pollutant removal. These species should be treated with cautious in the remediation of contaminated soils.