Abstract Plant-associated microbial communities play a vital role in host adaptation to environmental stress, yet their contributions to plant nickel (Ni) tolerance strategies remain unclear. It is not understood whether the same microbial community elicits similar responses across different plant species or regulates stress adaptation in a host-specific manner. Although microorganisms influence plant responses to metal toxicity by altering metal bioavailability in the rhizosphere, their potential to optimize plant metal uptake is less explored. In this study, we evaluated whether synthetic microbial communities enhance (Ni) uptake in two species with contrasting metal strategies: the hyperaccumulator Odontarrhena chalcidica and the Ni-excluding Arabidopsis arenosa. We hypothesized that soil microorganisms support plant metal adaptation by improving physiological function rather than altering soil metal availability. Our results show that O. chalcidica reached its full hyperaccumulating potential only when co-cultivated with a soil-derived microbial community, regardless of the microorganisms’ ability to mobilize Ni or promote plant growth. Microorganisms that enhanced Ni uptake had no effect on soil Ni availability. Microbial community analysis revealed species-specific microbiota assembly, with O. chalcidica being more responsive yet more selective. Serpentine-soil microbiota enhanced Ni uptake in O. chalcidica by upregulating iron-transporter genes, confirming reliance on Fe-transport pathways for Ni acquisition. In contrast, the same inoculum induced Zn-transporters and NRT2.1/NRT2.2 in A. arenosa, reflecting strategy of cation partitioning and nutrient-transport fine-tuning under Ni stress. These findings refine criteria for selecting microorganisms in phytoremediation and highlight that the functional impact of plant-associated microorganisms on metal handling outweigh their effects on metal solubility in soil.
Domka et al. (2025) studied this question.