Ecological effects of water and fertilizer coupling on poplar planting soil

While irrigation and fertilization are basic cultivation practices in poplar plantations on a global scale, the impact of these practices on the environment is not well understood. Here, we demonstrate that water-urea coupling and water-compound fertilizer coupling differentially impact soil ecosystems. We report that water-fertilizer coupling did not significantly alter taxonomic diversity indices (richness, evenness), but it did drive significant shifts in microbial community composition, reflected by changes in the relative abundance of specific taxa (e.g., core phyla) and their functional profiles. Water-urea coupling reduced Proteobacteria and Actinobacteria in non-rhizosphere soils while increasing Acidobacteria and Chloroflexi. In contrast, water-compound fertilizer coupling amplified Proteobacteria and Actinobacteria dominance in rhizosphere soils. Water-fertilizer coupling reshaped microbial composition and functional gene abundance linked to nitrogen and sulfur cycling, indicating a potential shift in microbial-mediated N and S transformation processes. Water-urea treatment enriched denitrification genes and dissimilatory nitrate reduction genes (napABC) in rhizosphere soil, while water-compound fertilizer treatment enhanced nitrification (amoABC, HAO) and denitrification gene abundance in both soils. For sulfur (S) cycling, water-urea treatment favored thiosulfate oxidation genes (SOX complex), whereas water-compound fertilizer treatment increased assimilatory sulfate reduction genes. Multi-omics integration linked these microbial dynamics to metabolic reprogramming—water-urea increased lipid and secondary metabolites in rhizosphere soils, while water-compound fertilizers elevated amino acid-associated metabolites in non-rhizosphere soils.