Achieving overyielding and efficient potentially toxic elements phytoremediation by constructing remediation plant communities

According to the ecological niche theory and stress gradient hypothesis, diverse communities consisting of hyperaccumulators, nursing plants, and pioneer plants could enhance community productivity and more efficiently extract potentially toxic elements (PTE) from the soil. To test this hypothesis, Pteris vittata L. (hyperaccumulator, denoted by E), Medicago sativa L. (tolerant/nurse plants, denoted by M), and Parthenocissus semicordata (Wall.) (tolerant/pioneer plants, denoted by P) were cultivated in monoculture and intercropped at 1/2/3 abundance levels. Seven treatments (E, M, P, EM, EP, MP, EMP) were carried out to explore the ecological effects and interspecific relationships within plant communities, and to assess their impact on the efficiency of PTE combined pollution remediation. All intercropping communities exhibited an overyielding effect, with the plant aboveground PTE accumulation (mg/m2) exceeding that of monoculture communities, in the order of EM > EP > EMP. The overyielding effect in EM was significant and dominated by complementary effects, with the aboveground biomass of Pteris vittata (EM-E) being 3.04 times greater than that of E. The plant aboveground of EM accumulated significantly higher levels of As, Cd, Pb, Cu, and Zn, reaching 1861.36, 48.01, 166.92, 53.89, and 2022.71 mg/m2, respectively, compared to other communities. Compared with the monoculture community, the accumulation of As, Cd and Zn in the plant aboveground of EM-E increased by 5.07%, 11.24% and 83.36%, respectively, and in EM-M by 48.43%, 76.01%, 8.84%, 28.09% and 51.52%, respectively. The microorganisms (Candidatus Solibacte, Candidatus Udaeobacter, Nitrosovibrio, Kaistobacter, Thiobacillus, etc.) involved in nutrient cycling in the rhizosphere soil of the intercropping community accounted for a large proportion, showing notably higher abundance compared to the monoculture community. Structural equation model analysis revealed that the variation in ecological effects had a direct or indirect impact on the enrichment of PTE by remediation plants through influencing soil PTE content and adjusting microbial community function.