Contrasting biotic and abiotic drivers of Glomeromycotina and Mucoromycotina mycorrhizal associations in field-grown durum wheat.

Mucoromycotina fine root endophytes (M-FRE), although commonly present in cultivated crops, represent a largely overlooked symbiosis, and their diversity and ecological functions under field conditions remain poorly understood. The co-occurrence of M-FRE and Glomeromycotina arbuscular mycorrhizal fungi (G-AMF) was assessed in field-grown durum wheat (Triticum turgidum subsp. durum), testing the effects of combined water and nitrogen stress on root colonization and fungal community diversity in roots, rhizosphere, and extra-radical hyphae. The M-FRE colonization was reduced under combined stress but was unaffected by wheat genotype. In contrast, G-AMF colonization varied among genotypes and was insensitive to this combined stress. While G-AMF colonization correlated with root traits, M-FRE abundance was rather determined by soil properties and the applied stress. Colonization by M-FRE but not by G-AMF correlated with nitrogen and phosphorus uptake in plant shoots. Partial 18 S metabarcoding detected 74 G-AMF taxa and 12 M-FRE taxa, some shared across compartments, revealing active growth of M-FRE extra-radical hyphae. Stress had contrasting effects on diversity: G-AMF alpha diversity remained stable, whereas M-FRE diversity declined, with stress driving distinct community structures for both groups. Collectively, our results suggest that M-FRE and G-AMF are structured by distinct ecological drivers, supporting functional differentiation between these morphologically similar symbioses.