Abstract:[Objective] Over a prolonged period of growth, the old tea plant ecosystem of Camellia sinensis ‘Fujian Shuixian’ in Gujing has acquired a distinctive fir flavor, with the mountainous environment playing a key role in shaping the tea quality. Microbial communities play a vital role in biogeochemical cycling within mountainous ecosystems. Nevertheless, the characteristics of the microbial community within the distinct old tea plant ecosystem remain incompletely understood. [Methods] Samples were collected from both the aboveground and belowground parts of the old C. sinensis ‘Fujian Shuixian’ tea garden in Gujing, situated in the central region of the Wuyishan National Park. The samples encompassed the phyllosphere and leaf endosphere, along with soils from the rhizosphere, non-rhizosphere, and surrounding regions. High-throughput sequencing of the 16S rRNA gene and internal transcribed spacer (ITS) region were carried out to assess the bacterial and fungal diversity, respectively. [Results] The richness and diversity of bacterial and fungal communities in the aboveground part were markedly lower than those in the belowground part. Within co-occurrence networks, the modularity index for taxa networks in each niche exceeded 0.4, and the positive correlations in interactions among microbial taxa are greater than the competition. The prevailing phyla, with the relative abundance greater than 1%, were Proteobacteria, Acidobacteriota, Actinobacteriota, Ascomycota, and Basidiomycota, which were present in both above and belowground habitats. Notably, the relative abundance of Proteobacteria, Actinobacteria, and Ascomycetes aboveground surpassed that belowground, whereas that of Acidobacteria and Basidiomycetes displayed an opposite pattern (P<0.05). The prominent genera (with the abundance exceeding 1%) identified were Methylobacterium-Methylorubrum, Sphingomonas, Pseudomonas, Amnibacterium, Bacillus, Cladosporium, and Fusarium. These genera potentially served as crucial biomarkers in the ecological niches of C. sinensis ‘Fujian Shuixian’ within the old tea plant ecosystem in Gujing. [Conclusion] The present study unveiled the unique attributes of bacterial and fungal communities within the old tea plant ecosystem of C. sinensis ‘Fujian Shuixian’ in Gujing, delivering valuable scientific insights for disease prevention and biocontrol in tea plant cultivation, tea quality improvement, and the exploration of functional microbial resources.