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-18g encoding cinnamoyl-CoA hydratase/dehydrogenase. Overexpression of CHD-18g 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.
Liao et al. (Thu,) studied this question.