β-Caryophyllene gradients act as ecological filters shaping microbial life-history strategies via iron competition.

Plant-emitted volatile organic compounds (VOCs) are increasingly recognized as key mediators of plant-microbe interactions, yet how they shape microbial community assembly and adaptive strategies remains unclear. Here, using the widespread plant sesquiterpene β-caryophyllene as a model VOC, we demonstrate that plant volatiles drive dose-dependent ecological filtering and microbial adaptation, governed by life-history trade-offs and resource availability. Soil microcosm experiments revealed that low concentrations of β-caryophyllene selectively enrich competitive bacterial taxa, whereas high concentrations favor ruderal, fast-growing opportunists, restructuring communities along a competitor-stress tolerator-ruderal axis. Focusing on representative taxa, Bacillus subtilis and Pseudomonas aeruginosa, we show that these contrasting ecological outcomes are underpinned by divergent physiological, metabolic, and transcriptional reprogramming. Across both taxa, low-dose β-caryophyllene consistently induces siderophore biosynthesis, identifying iron availability as a central integrator of volatile perception and response. Experimental manipulation of iron reprogrammed growth, carbon utilization, and antibiotic resistance, gating whether β-caryophyllene functions as a signal that primes competition or as a stressor that selects for ruderal traits. Together, our work offers critical insights into the VOC-mediated microbiome management for ecological restoration and sustainable agriculture.