Keystone and potentiator taxa in hyperaccumulator rhizospheres: A new perspective for microbiome-assisted...

Soil heavy-metal contamination threatens agroecosystem functioning, and hyperaccumulators, together with their rhizosphere microbiomes, offer promise for the phytoremediation of contaminated soils. Most rhizosphere microbiome studies have emphasized keystone taxa, but abundant and stable non-keystone members may also contribute to community functioning. Here, we examined the rhizosphere microbiome of the Ni hyperaccumulator Odontarrhena chalcidica using a combination of amplicon and metagenomic sequencing. Keystone taxa were identified as taxa supported by multiple ecological inference approaches, whereas potentiator taxa were defined as abundant and stable taxa that were not identified as keystones. We then compared their taxonomic composition, functional potential, and model-predicted metabolic interactions. Keystone and potentiator taxa were taxonomically distinct. Potentiator taxa showed broader functional potential than keystone taxa, suggesting that these stable non-keystone members may contribute functions that are overlooked by keystone-focused analyses alone. Genome-scale metabolic modeling further predicted greater metabolite exchange in mixed keystone-potentiator assemblages than in single-role assemblages, with model-predicted metabolic support directed mainly from potentiator taxa to keystone taxa. These findings indicate that abundant and stable non-keystone taxa can complement keystone taxa in the rhizosphere microbiome of a Ni hyperaccumulator. More broadly, this study provides an analytical strategy for identifying candidate microbial combinations that may support microbiome-assisted phytoremediation of metal-contaminated soils.