Background and aims Rhizosphere microorganisms play a critical role in plant growth, particularly in degraded lands. However, the characteristics of rhizosphere microbial communities, assembly mechanisms, and their influencing factors in Pinus elliottii plantations on sandy lands in the Poyang Lake Basin, China, remain unclear. Methods We investigated the composition of bulk soil and rhizosphere microbial communities in P. elliottii plantations by Illumina Miseq sequencing. Community assembly and cross-domain network analyses were used to reveal the microbial community assembly mechanisms and co-occurrence patterns, and to identify the main biotic and abiotic factors influencing them. Results The P. elliottii rhizosphere was significantly enriched with Burkholderia-Caballeronia-Paraburkholderia. The composition of the fungal community did not exhibit significant differences between compartments. The P. elliottii rhizosphere had a notably simplified bacterial-fungal co-occurrence network, with keystone microorganisms potentially exerting significant roles in plantation establishment and soil nitrogen and phosphorus cycling. Bacterial community assembly was governed by both deterministic and stochastic processes, whereas fungal communities were dominated by stochastic processes. A significant correlation was detected between bacterial communities and fungal richness. Differences in fungal richness were significantly correlated with the rhizosphere bacterial community beta-Nearest Taxon Index, whereby a larger difference in fungal richness between samples led to a higher percentage of variable selection in the process of rhizosphere bacterial community assembly. Conclusion This study highlights the strong association between P. elliottii and Burkholderia-Caballeronia-Paraburkholderia and underscores the significant role of fungal richness in the bacterial community assembly in the rhizosphere of P. elliottii in sandy soils.