Climate and Soil Factors Shape Microbial Diversity and Key Taxa Influencing Poplar Growth in Plantations

In the poplar plantations, soil microorganisms—particularly key microbial taxa—can have a profound impact on plant growth through their responses to environmental changes. However, there remains a lack of understanding of how environmental factors drive microbial diversity and key taxa, and how these, in turn, affect poplar growth. This study investigated 6-year-old poplar plantations across three regions of the North China Plain (Beijing, Hebei, and Henan). Combined with high-throughput cultivation and pot experiments, the growth-promoting effects of culturable key microbial strains on poplars were assessed. The results showed significant differences in climate indices, poplar growth traits, soil physicochemical properties, and soil microbial communities among the plantation regions (p < 0.05). A synthetic community comprising key strains (Acinetobacter-Aa20, Bacillus-Aa15, Bacillus-Ba9, and Bacillus-Ab26) significantly promoted poplar seedling growth. The results indicated that mean annual precipitation and mean annual temperature influence soil nutrient availability, thereby affecting poplar growth. Key taxa may indirectly promote poplar growth by being recruited through soil nutrient dynamics. This study provides important ecological insights into the interaction mechanisms among environmental factors, plants, soil, and microorganisms in poplar plantation ecosystems.