Stand Age–Associated Rhizosphere Bacterial Succession in the Desert Shrub Haloxylon ammodendron

Haloxylon ammodendron is a keystone shrub widely used for ecological restoration in arid regions of Northwest China. However, how rhizosphere bacterial communities reorganize across stand ages remains poorly understood. Rhizosphere soils were collected from one-, three-, and six-year-old stands using full-length 16S rRNA sequencing. Although alpha diversity remained relatively stable, beta diversity revealed pronounced community turnover. The dominant phyla were conserved across stands, whereas genus- and species-level composition shifted systematically along the age gradient. Younger stands were enriched in stress-tolerant and early colonizing taxa, intermediate stands showed increased representation of plant-associated and nitrogen-cycling bacteria, and older stands harbored taxa associated with complex carbon turnover and stress adaptation. Network analysis suggested modular co-occurrence patterns across stand ages and PICRUSt2-based functional inference indicated a conserved core metabolic repertoire accompanied by gradual ecological differentiation in pathways related to resource utilization and environmental response. Together, these findings suggest a stand age–associated pattern of rhizosphere bacterial succession and provide insight into microbial community differentiation in a desert shrub system.