Plant functional group and soil character: two effective factors to define endophytic fungal diversity in a gypsum-rich environment.

Gypsum soils impose severe physiological and ecological constraints on plants, yet the diversity and ecological drivers of their associated fungal endophytes remain poorly understood. We examined the taxonomy, diversity, and community composition of endophytic fungi associated with ten plant species representing three functional groups-wide gypsophiles, narrow gypsophiles, and gypsovags-in a gypsum-rich desert ecosystem in central Iran. From 11,520 plant fragments collected over two years, 4482 fungal isolates were obtained and assigned to 44 operational taxonomic units (OTUs) belonging to 8 classes and 14 orders, with Ascomycota predominating. Wide gypsophiles harbored the most diverse and abundant fungal assemblages, followed by narrow gypsophiles and gypsovags, suggesting an association between plant gypsum tolerance and endophyte diversity within the studied system. Mixed-effects models showed that plant functional group, organ type, and soil variables-particularly cation exchange capacity, saturated soil moisture, and bicarbonate concentration-significantly influenced OTU richness and Shannon diversity. PERMANOVA revealed that host species was the strongest determinant of community composition, followed by organ type, plant functional group, and ten soil variables related to nutrient availability, salinity, and ionic balance. NMDS ordinations showed distinct community clusters across functional groups, with wide and narrow gypsophiles partially overlapping and gypsovags forming clearly separated assemblages. This study provides the first comprehensive assessment of endophytic fungal diversity across plant functional groups in gypsum habitats. Our results highlight strong host specificity and substantial environmental filtering and provide a basis for future studies investigating the potential functional roles of fungal endophytes in plant adaptation to gypsum-rich environments.