CHD-18 g-modulated Pseudomonas taxa support poplar salt tolerance.

Against the background of global climate change, soil salinization has emerged as a major abiotic stressor constraining agroforestry productivity worldwide. Root-recruited microbes enhance plant stress resilience, and host-microbe interactions depend on plant root metabolism. Stress-tolerant plant genotypes exhibit a marked capacity to enrich beneficial root-associated microbes through specialized metabolic responses, thereby facilitating phenotypic plasticity. However, the molecular mechanisms underlying these plant-microbe interactions remain unclear. In this study, we compared salt tolerance among three poplar varieties under aseptic and non-aseptic conditions, and analyzed their rhizosphere bacterial community responses to salt stress. We found that microbial inoculation modulated poplar salt tolerance, and poplar shaped rhizosphere bacterial communities in a genotype-dependent manner. Transcriptome sequencing and targeted metabolomic analysis indicated that salt-tolerant poplar plants preferentially activate the phenylpropanoid biosynthesis pathway, accompanied by the enhanced root secretion of benzoic acid (BA) and salicylic acid (SA) and up-regulation of CHD-18 g encoding cinnamoyl-CoA hydratase/dehydrogenase. Overexpression of CHD-18 g increased rhizosphere Pseudomonas abundance by enhancing BA and SA biosynthesis. Binary interaction assays further showed that the BA-induced Pseudomonas taxa mitigated salt stress and promoted poplar growth under salt stress. Our findings propose a framework linking host gene expression, root metabolism, and key microbial taxa in conferring salt tolerance. This work uncovers a metabolic signaling mechanism by which trees shape their root microbiome to enhance stress adaptation, offering actionable genetic and ecological strategies for improving tree resilience in sustainable agroforestry systems.