Interaction between rhizobacterial community and host root metabolism influences poplar salt tolerance

Soil salinization worldwide affects agroforestry, restraining output and functions of farmland and forest ecosystems. Soil microbiota play vital roles in plant growth and resistance to stress, but how plants interact with root microbiomes to fight adverse environments remains elusive. Here, we employed high-throughput sequencing to investigate the rhizobacterial community composition of three poplar varieties that were Populus davidiana × P. bolleana Loucne (SXY), P. deltoides × P. euramericana "Nanlin 895" (NL895), and P. alba × P. glandulosa "84K" (84K) under salt stress. Our results showed that no differences in growth parameters and damage indices were observed across varieties before treatments. Furthermore, SXY exhibited the highest salt tolerance, characterized by the highest growth parameters and lowest damage indices under salt stress, while NL895 was the most sensitive genotype. The 16S rRNA gene sequencing unveiled the lowest diversity and distinct composition in the rhizobacterial community of SXY compared to other varieties. SXY accumulated a higher abundance of Pseudomonas, Pseudoxanthomonas, and Rhizobiaceae in the rhizosphere, which showed positive correlations with host salt tolerance. Moreover, metabolomic analysis revealed higher levels of certain secondary metabolites in SXY roots than in the roots of the other varieties. Four metabolites, including D-threitol, maslinic acid, 4',5-dihydroxy-7-methoxyflavanone, and trans-3-coumaric acid, were identified as key regulators that potentially mediate the enrichment of salt tolerance-associated rhizobacterial taxa. Our findings indicate an interaction between root metabolism and rhizosphere microbiome in poplar adaptation to salt stress, providing a theoretical basis for directional modulation of plant resistance under global change.IMPORTANCEAgroforestry frequently encounters soil salinization that limits crop yields and ecosystem services. Soil microbiota plays an important role in plant adaptation to stress, but their interaction mechanisms with host roots remain unclear. Through combining high-throughput sequencing and root metabolome analysis, we unraveled the interactions between rhizobacterial communities and host root metabolism, as well as their role in plant adaptation to salt stress, providing new strategies for microbial application under global change.