Correlation analysis of lead stress-induced alterations in root metabolome and rhizosphere microbiome of Cuminum cyminum L.

Lead (Pb) contamination in agricultural soils poses serious threats to crop production and food safety. Cuminum cyminum L. is an important spice crop widely cultivated in arid regions, but its rhizosphere responses to Pb stress remain poorly understood. Here we conducted a field plot experiment with four Pb treatment levels (0, 400, 800, and 1200 mg/kg) and employed an integrated approach combining soil physicochemical and enzymatic analyses, metagenomics, and root metabolomics to characterize the rhizosphere of C. cyminum after 40 days of Pb exposure. Pb significantly decreased soil pH, organic matter, nitrogen availability, and available phosphorus and potassium, while altering soil enzyme activities by suppressing urease and acid phosphatase and enhancing catalase activity. Pb stress reshaped rhizosphere microbial communities by increasing microbial richness at low and moderate Pb levels but reducing community evenness under high Pb stress. Metal-tolerant taxa, including Sphingomonas, Arenimonas, and Gemmatimonas, were selectively enriched. Functional analyses revealed a broad enhancement of microbial metabolic potential, particularly in amino acid, carbohydrate, and energy metabolism pathways. Concurrently, Pb exposure correlated with extensive root metabolic reprogramming, characterized by accumulation of amino acids, organic acids, and flavonoids. The random forest results indicated that soil physicochemical properties had a stronger correlation with plant growth than root metabolites or rhizosphere microorganisms under Pb stress conditions. Overall, this study reveals a coordinated rhizosphere strategy of C. cyminum to Pb stress, providing new insights into heavy metal adaptation mechanisms in spice crops and informing sustainable cultivation in Pb-contaminated soils.