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

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.