Targeted rewiring of the rhizosphere metabolite-microbe axis restores phosphorus acquisition in inefficient citrus rootstock.

Abstract

Low phosphorus (P) availability limits citrus production, while genotypic determinants governing rhizosphere P mobilization remain elusive. Here, we investigated P-acquisition strategies in citrus rootstocks. We performed a systematic screening of citrus rootstocks under P-deficient conditions and identified two contrasting genotypes: P-efficient Citrus tangerina and P-inefficient Citrus junos. Comparative metabolomics, microbiome profiling, targeted strain isolation, and inoculation assays were combined to unravel metabolic and microbial drivers governing P mobilization. The superior P acquisition of C. tangerina stemmed from a unique root-exudate profile enriched in 2-hydroxyflavanone, scopoletin, raffinose, and gallic acid. These metabolites selectively enriched Methylobacterium sp. strain HA110, a robust P-solubilizing bacterium. Exogenous exudate application enhanced C. junos P acquisition, yet this beneficial effect was abolished under soil sterilization, demonstrating an essential role of microbiota. Combined supplementation of the metabolites and strain HA110 enhanced rhizosphere P activation, which in turn strengthened the P-acquisition capacity of C. junos and consequently stimulated its growth. Collectively, these findings uncover a novel metabolite-microbe axis: P-efficient rootstocks reshape their rhizosphere microbiome through specific exudates. This axis is amenable to rational reconfiguration to restore P acquisition in P-inefficient genotypes, laying a theoretical basis for exudate-derived biofertilizers to boost P-use efficiency in sustainable citriculture.

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