Biodiversity of Eucalyptus endophytic fungi across different climates in Iran.

Endophytic fungi are crucial for plant health, but the relative importance of climate versus host factors in shaping their communities is not fully understood. This study investigates the hypothesis that macro-climate is one of the primary drivers of endophytic fungal diversity and composition in Eucalyptus camaldulensis across different regions in Iran. A total of 712 fungal isolates were isolated from leaves, branches, and fruits across five provinces (Alborz, Isfahan, Mazandaran, Qom, and Tehran) spanning arid to humid climates. Cultivation and morphological/molecular identification revealed a clear diversity gradient, with the highest species richness, Shannon diversity, and colonization frequency in the humid province of Mazandaran, and the lowest in the semi-arid and arid provinces of Alborz and Qom, respectively. Community composition shifted significantly along this climatic gradient: arid sites were dominated by stress-tolerant generalists (e.g., Alternaria), while the humid site supported a balanced community of specialists (e.g., Neofusicoccum). Across all climates, tissue type was a consistent secondary filter, with leaves harboring the most diverse communities, followed by branches and fruits. These results demonstrate a hierarchical assembly where climate filters the regional species pool, and host tissue type then fine-tunes the local community. This study provides the first comprehensive baseline of E. camaldulensis endophytes in Iran and highlights the vulnerability of these symbiotic systems to climate change, while also identifying them as a valuable resource for biotechnology.