Host Identity and Urban Space Structure Phyllosphere Bacterial Communities Through Compositional Turnover in a Tropical Andean City

Phyllosphere bacterial communities of urban vegetation remain poorly characterised in tropical Andean cities, where high year-round ultraviolet irradiance and compact valley topography differ from the temperate systems that dominate the literature. We characterised epiphytic bacterial communities on fifteen plants of three widely planted species: Mangifera indica L. (mango; Anacardiaceae), Terminalia catappa L. (tropical almond; Combretaceae) and Thunbergia grandiflora (Roxb. ex Rottler) Roxb. (blue trumpet vine; Acanthaceae), one per species in each of five urban zones of Medellín, Colombia, sampled in five surveys over nineteen months with three spatial subsamples per plant and survey (224 samples; 16S rRNA V3–V4). Host species and urban zone structured community composition across all five distance metrics examined (R2 = 0.19–0.30 and 0.34–0.37), yet neither affected any measure of alpha diversity. Partitioning beta diversity resolved why: host species and urban zone acted exclusively through taxon turnover, whereas survey acted exclusively through nestedness, driving a fivefold decline in richness that tracked a monotonic rise in relative humidity across the study period. The two spatial filters explained statistically independent fractions of variation (unique adjusted R2 = 0.236 and 0.174; shared fraction indistinguishable from zero). Bacterial communities from different parts of a single canopy differed by 69% of the dissimilarity separating host species, and this within-plant coherence weakened as communities contracted. Deterministic host selection and stochastic temporal contraction therefore appear to operate concurrently through complementary mechanisms in this system.