Arbuscular and fine root-endophytic mycorrhizal fungi forage differently for nutrients in a seminatural temperate grassland

The acquisition of P and N from soil and their exchange for fixed C are key functions of mycorrhizal fungi in their symbiotic relationship with host plants. Additional contribution to plant nutrition is possible when hyphae proliferate into soil space not directly accessible to plant roots or when they locate nutrient-rich patches more effectively than plant roots. We performed a field-based experiment in a seminatural grassland. Community composition, diversity, and root colonisation intensity of mycorrhizal fungi was compared across different types of substrate patches (enriched or not with inorganic N, P or both), between two exposure times, and with unmanipulated soil and patches enriched with plant biomass. Beside evaluating the response of the communities of arbuscular mycorrhizal fungi (G-AMF) and fine root endophytes (M-FRE), we estimated foraging speed and precision of multiple taxa within these two groups. We compared the relative abundance of both groups using molecular barcoding. While G-AMF responded in community composition and diversity to inorganic and organic N enrichment, M-FRE did not discriminate among diferentially nutrient-enriched patches. Individual taxa varied in foraging response, but G-AMF were slower and possibly more discriminatory than M-FRE in occupying patches differing in N and/or P-enrichment. Particularly two virtual taxa of the Rhizophagus irregularis morphospecies of the G-AMF grew preferentially into the N-enriched patches. We thus conclude that there exist important differences in the strategies of soil exploration for nutrients within both fungal groups.