Plant compartment and understory habitat jointly shape endophytic bacterial communities in Monochasma savatieri

Monochasma savatieri is a rare medicinal plant endemic to China that currently faces extinction, with wild-simulated understory cultivation representing a key conservation strategy. Endophytic bacteria play important roles in nutrient acquisition and environmental adaptation of hemiparasitic plants; however, how the understory environments influence above- and belowground endophytic bacterial communities remains poorly understood.

We collected soil and plant tissue samples from four contrasting understory habitats (Pinus massoniana, Camellia oleifera, Phyllostachys edulis, and Gardenia jasminoides). The endophytic bacterial communities were characterized by 16S rRNA gene sequencing. The soil physicochemical properties were measured to identify environmental drivers. Multivariate statistics, including permutational multivariate analysis of variance (PERMANOVA), redundancy analysis (RDA), and Mantel tests, were applied to link the community variation with environmental factors.

Permutational multivariate analysis of variance revealed that the type of plant tissue, habitat, and their interaction (all p < 0.001) significantly shaped the endophytic community structure. Belowground tissues generally harbored higher diversity than aboveground tissues, although this pattern was habitat-dependent. Each habitat enriched distinct bacterial genera. Functional predictions showed a complementary pattern: aboveground communities were enriched in sensing-related pathways, whereas belowground communities showed higher abundances of degradation-associated pathways. RDA identified the soil total and available potassium as strong environmental correlates of community differentiation.

The findings of this study demonstrate that plant compartment and understory habitat jointly shape endophytic bacterial communities in M. savatieri, with potassium availability as a key correlate. However, because each habitat was represented by a single geographic site, the vegetation type is confounded with the location, climate, and soil properties; therefore, our inferences are correlative rather than causal. Within these constraints, the findings help identify candidate taxa and environmental associations that provide testable hypotheses for future cultivation and microecological research on this rare medicinal plant.