Genotype‐Dependent Rhizosphere Microbiome Assembly Improves Potassium Use Efficiency in Pear Rootstocks Under Low Potassium Stress

ABSTRACT Potassium (K) is a vital nutrient for fruit quality in pears ( Pyrus spp.), and rhizosphere microbes play a critical role in enhancing plant K uptake and utilization. To investigate the genotype‐dependent influences of the rhizosphere microbiome on potassium use efficiency (KUE) in pears, we compared two rootstocks with contrasting KUE ( Pyrus betulaefolia and Pyrus ussuriensis ) using integrated pot and long‐term field experiments, 16S rRNA amplicon sequencing, and metagenomic analyses. Synthetic community (SynCom) inoculation and transcriptome profiling were employed to elucidate the mechanisms underlying enhanced K acquisition. Under low‐K conditions, P. betulaefolia recruited distinct microbial communities, which significantly improved K accumulation by upregulating genes (e.g., ATP1A, kdPB , and COG3158 ) associated with K transport and homoeostasis. Field trials further confirmed that P. betulaefolia ‐grafted trees sustained higher Bacillaceae abundance, superior fruit quality, and elevated K content than P. ussuriensis under K‐deficient conditions. SynComs constructed from five Bacillaceae strains enhanced low‐K tolerance by promoting root metabolic activity, stimulating root hair development, modulating K⁺ transporter (e.g., NRT2.4 ) expression, and activating calcium‐dependent signalling pathways. Inoculation with SynComs led to substantial improvements under K limitation, including a 105.86% increase in plant biomass, a 164.99% increase in K accumulation, and a 125.91% enhancement in the aboveground K utilisation index. These findings reveal that genotype‐driven enrichment of Bacillaceae ‐dominated microbiomes significantly enhances pear KUE, offering mechanistic insights to guide the development of microbiome‐based bioinoculants and breeding of “microbiome‐responsive” rootstocks for sustainable fruit production under K‐limiting conditions.