Areca catechu Bark-Associated Microbial Diversity and Community Composition: Monoculture vs. Stereo Cultivation with Dendrobium nobile

Stereo cultivation (SC) of Dendrobium nobile (D. nobile) on Areca catechu (A. catechu) trunks is practised in tropical agroforestry, yet its association with bark-associated microbial communities remains poorly characterised. In this study, existing A. catechu–D. nobile SC and A. catechu monoculture (MC) fields were compared at three sites on Hainan Island, China, to investigate differences in bark-associated bacterial and fungal diversity and community composition on A. catechu and their associations with environmental conditions. At each site, three spatially separated sampling plots were randomly selected within each cultivation system, yielding 18 plot-level composite samples (3 sites × 3 plots × 2 systems). All statistical analyses were interpreted as exploratory. Bark-associated bacterial and fungal communities were characterised using 16S rRNA and ITS amplicon sequencing, respectively. Bacterial Shannon, fungal ACE and Chao1 indices under SC were significantly higher than MC (p < 0.05). PERMANOVA revealed significant bacterial and fungal community composition differences between SC and MC. Proteobacteria, Cyanobacteria and Acidobacteriota dominated bacterial communities in both SC and MC, together accounting for approximately 75% of the relative abundance. SC showed a higher relative abundance of Acidobacteriota than MC (22.3% vs. 8.46%; FDR-adjusted p < 0.05), with the same directional pattern across all three sites. Fungal communities were dominated by Ascomycota (approximately 80%) in both systems, and the observed differences in phylum-level relative abundances were not statistically significant. LEfSe analysis identified Acetobacterales and Acetobacteraceae (bacteria) and Pleosporales and Nectriaceae (fungi) as taxa distinguishing SC from MC, with higher relative abundances under SC. PICRUSt2 functional prediction indicated higher relative abundances of glycan biosynthesis and metabolism and the metabolism of terpenoids and polyketides under SC than under MC. FUNGuild analysis also showed some differences in fungal trophic guild composition between the two systems. These findings suggest associations between SC systems and bark-associated microbial communities. However, SC microbial profiles may reflect a D. nobile–cow dung–bark complex rather than A. catechu bark alone, which preclude causal attribution to individual components. Further research is needed to clarify their respective contributions.