Enhanced phytoextraction of manganese and cadmium by Polygonum lapathifolium L. via Enterobacter sp. inoculation: Roles of rhizosphere regulation and endophytic microbiome assembly.

Plant growth-promoting bacteria (PGPB) can enhance phytoremediation, but whether inoculation alters rhizosphere microbial abundance and elicits tissue-specific endophytic responses remains unclear. Here, Enterobacter sp. was applied to improve Mn/Cd phytoextraction by Polygonum lapathifolium L. Inoculation decreased rhizosphere pH and increased acid-extractable Mn and Cd by 11.8% and 45.5%, respectively, accompanied by enhanced nutrient availability and C, N and P cycling enzyme activities. It also altered rhizosphere bacterial and fungal community structure, increased their absolute abundances and functional potential, and markedly increased rhizosphere Enterobacter abundance. In parallel, inoculation induced adaptive shifts in plant endophytic microbial communities, as reflected by higher root bacterial community-level rrn copy numbers but lower values in leaves, together with enhanced modularity of the endophytic interaction network under the C1.0 (9.50 ×1010 CFU/pot) treatment, predominated by Pseudomonadota and Actinomycetota. Path analysis revealed that rhizosphere bacteria indirectly promoted Mn/Cd phytoextraction by regulating soil properties, while alleviation of oxidative stress sustained metal uptake. Inoculation reduced H2O2 and ·O2- levels, enhanced antioxidant capacity, and increased plant growth and metal accumulation. Overall, Enterobacter sp. inoculation enhanced phytoextraction through quantitative and compositional changes in rhizosphere microbiota, tissue-specific endophytic responses, and improved plant stress tolerance, supporting its application in Mn-Cd contaminated soils.