Shaping Fungal Communities in Cenchrus setaceus: Host Condition and Habitat Filtering

We investigated the leaf-associated fungal communities of Cenchrus setaceus across a host condition gradient (high- vs. low-condition plants) and environmental zones (coast vs. hill; trade-wind exposure) on Tenerife (TF) and La Palma (LP). We hypothesized that community assembly reflects both host-driven deterministic filtering and abiotic promotion of richness in favourable environments via two mechanisms: (i) high-condition plants promote stable, guild-structured communities; (ii) humid, topographically buffered zones enhance fungal richness, especially for endophytes and saprotrophs. Nanopore sequencing and functional guild annotation revealed island- and zone-specific fungal assemblages. In TF, low-condition plants were associated with genera linked to stressed or exposed conditions whereas high-condition plants, especially in humid northern hills, supported more recurrent yeast-like and niche-associated taxa. In LP, high-condition plants in eastern hill zones were associated with distinct taxa, while drier western coastal low-condition plants were enriched in stress-related fungi. Fungal genera richness (Hill0) was consistently higher in low-condition plants (TF: 146 vs. 95; LP: 94 vs. 76; p < 0.05), while Shannon diversity diverged: greater in high-condition plants on LP (3.29 vs. 2.98), but lower on TF (3.10 vs. 3.28; p < 0.05). Community structure was shaped primarily by host condition in TF (PERMANOVA R² = 8.6%, p < 0.05), and by zone in LP (R² = 15.0%, p < 0.05). On TF, low-condition plants hosted significantly higher richness of saprotrophic, endophytic and plant-pathogenic genera (all p ≤ 0.001), whereas in LP zone × condition effects shaped guild richness patterns, with saprotroph richness increasing 2.66-fold in high condition plants from eastern hills relative to the eastern coast. Overall, high-condition plants supported less diverse but compositionally more stable fungal communities, while favourable environments enhanced guild richness independently of host condition.