Dominant core bacterial taxa show stronger associations with rhizosphere soil multifunctionality than core rare taxa in Pinus tabuliformis planted forests along a Loess Plateau aridity gradient

Drought intensification threatens ecosystem functioning of Pinus tabuliformis planted forests on the Loess Plateau. Soil multifunctionality integrates key processes, including nutrient cycling, organic matter transformation, and enzyme activities, thereby supporting planted forests ecosystem functions. Rhizosphere core microorganisms regulate these processes and influence soil multifunctionality. However, core microbial communities are not homogeneous, and how abundance-based ecological differentiation affects their drought responses and contributions to soil multifunctionality remains unclear. Along a natural aridity gradient, rhizosphere soils were collected from mature P. tabuliformis planted forests across three regions of the Loess Plateau. Core bacterial taxa were classified into dominant core and core rare taxa based on 16S rRNA sequencing, prevalence, and relative abundance. We evaluated their ecological differentiation in terms of diversity, niche breadth, drought responses, co-occurrence network topology, and associations with soil multifunctionality. Dominant core and core rare taxa exhibited contrasting community characteristics and drought response patterns. Dominant core taxa showed higher α-diversity, broader niche breadth, and lower compositional variation, whereas core rare taxa displayed higher β-diversity and stronger species turnover. With increasing aridity (decreasing aridity index), diversity increased in both groups, but core rare taxa diversity was more strongly associated with the aridity gradient ( R 2 = 0.81, P < 0.001). Core rare taxa harbored a higher proportion of drought-responsive amplicon sequence variants (ASVs) (61.29% vs. 49.48%), whereas dominant core taxa showed stronger response intensity, with 17.42% of ASVs simultaneously exhibiting large effect sizes (| β | > 0.5) and high explanatory power ( R 2 > 0.6), suggesting a higher prevalence of aridity responses among core rare taxa and stronger abundance-based responses in dominant core taxa. Co-occurrence network analyses revealed distinct topological roles for the two groups. Dominant core taxa formed the main network framework because of their higher abundance and node representation, whereas core rare taxa included a higher proportion of keystone nodes involved in network organization. Dominant core networks exhibited higher global connectivity, while core rare networks showed stronger local clustering and modularity. With increasing aridity, dominant core network complexity decreased significantly ( P < 0.001), whereas core rare network complexity showed an increasing trend without reaching statistical significance ( P > 0.05). More importantly, dominant core-associated traits independently explained 33.4% of the variation in soil multifunctionality, exceeding the contribution of core rare taxa (6.3%), with network complexity exhibiting the highest relative importance (32.54%). Piecewise structural equation modeling further indicated that dominant core network complexity potentially links aridity variation to soil multifunctionality. Overall, this study reveals abundance-based ecological differentiation within the core microbiome and provides new insights into microbial contributions to ecosystem functioning under increasing aridity.