Distinct rhizobacteria recruitment under copper stress contributes to the different copper-accumulating capacities of two Elsholtzia species (Lamiaceae)

Background and aims This study aims at identifying Cu accumulators from Elsholtzia and uncovering the rhizospheric mechanisms for improving the phytoremediation of Cu-contaminated soils. Methods The Cu accumulation capacities of ten Elsholtzia species were investigated in Cu-polluted soil, and two species with the largest differences in Cu accumulation capacities were selected to verify the results and to analyze their rhizospheric response characteristics (e.g., changes in Cu availability and rhizospheric bacterial community) to Cu stress in soils spiked with 0, 250, and 500 mg kg −1 Cu. Results These 10 Elsholtzia species showed various Cu accumulation capacities (Cu bioconcentration factors: 0.55–1.86 in shoots, 1.13–5.27 in roots), and most of them showed the potential for Cu phytostabilization. Among them, E. eriocalyx and E. winitiana could both tolerate up to 500 mg kg −1 Cu in soils but showed high- and low-Cu-accumulating capacities, respectively. Rhizospheric analysis indicated that specific rhizobacteria recruited by E. eriocalyx and E. winitiana were responsible for their differential Cu uptake. Several different plant growth-promoting rhizobacteria (e.g., Sphingomonas , Gemmatimonas , Devosia , and Flavisolibacter ) might contribute to the plant vitality of E. eriocalyx under Cu stress. Moreover, the dominant Sphingomonas was responsible for the higher Cu accumulation in E. eriocalyx plants. However, the dominance of several rhizobacteria in the Planctomycetes phylum might participate in Cu immobilization, thus decreasing Cu uptake by E. winitian . Conclusion This study identifies novel Elsholtzia species resources for the phytoremediation of Cu-contaminated soils and improves our understanding of the roles of rhizobacteria in regulating the Cu accumulation capacities of plants.