Soil bacterial diversity drives shifts in dominant plants' fine root C:N:P stoichiometry across an altitudinal gradient

Fine roots (diameter ≤ 2 mm) play a crucial role in regulating the biogeochemical cycles of mountain ecosystems, yet how their stoichiometric characteristics are influenced by rhizosphere microorganisms and their functional genes remains poorly understood. This study examined six vegetation zones spanning an altitude range of 1350–2950 m in the Helan Mountains, China, focusing on the rhizosphere of dominant plants. Specifically, it investigates fine root carbon (C), nitrogen (N), and phosphorus (P) contents, their stoichiometric ratios, microbial diversity, and the enrichment of functional genes linked to C, N, and P cycling processes. For each plant life form (arbor, shrub, and herb), sampling was carried out along the altitudinal gradient, targeting four specific elevations where each life form dominates. Furthermore, the research evaluated the key factors that influence fine root stoichiometric ratios. We found that as altitude increases, arbor species trigger a cascade effect through coordinated reductions in soil nutrient (soil organic carbon, total nitrogen, total phosphorus), and microbial diversity, which drives adaptive differentiation in fine root stoichiometry. Meanwhile, under the same lifeform, the primary factor influencing fine root stoichiometry for different plants at different altitudes is plant species. In the microbial driving mechanism, bacterial diversity emerged as the primary determinant of fine root stoichiometry in dominant plants. Additionally, the enrichment of microbial C, N, and P cycling functional genes had no significant impact on fine root stoichiometry. Our findings provide insights for ecological restoration and conservation to enhance the stability and sustainability of mountain ecosystems.