Agricultural management and pesticide use reduce the functioning of beneficial plant symbionts.

Phosphorus (P) acquisition is key for plant growth. Arbuscular mycorrhizal fungi (AMF) help plants acquire P from soil. Understanding which factors drive AMF-supported nutrient uptake is essential to develop more sustainable agroecosystems. Here we collected soils from 150 cereal fields and 60 non-cropped grassland sites across a 3,000 km trans-European gradient. In a greenhouse experiment, we tested the ability of AMF in these soils to forage for the radioisotope 33 P from a hyphal compartment. AMF communities in grassland soils were much more efficient in acquiring 33 P and transferred 64% more 33 P to plants compared with AMF in cropland soils. Fungicide application best explained hyphal 33 P transfer in cropland soils. The use of fungicides and subsequent decline in AMF richness in croplands reduced 33 P uptake by 43%. Our results suggest that land-use intensity and fungicide use are major deterrents to the functioning and natural nutrient uptake capacity of AMF in agroecosystems.