Abstract
Most crop species form a symbiotic association with arbuscular mycorrhizal (AM) fungi, receiving plant photosynthate and exchanging nutrients from the soil. The plant carbon (C) allocation to AM fungi and the nitrogen feedback are rarely studied together. In this study, a dual 13CO2 and 15NH415NO3 pulse labelling experiment was carried out to determine the allocation of recent photosynthates to mycorrhizal hyphae and the translocation of N absorbed by hyphae to strawberry plants. Plants were grown in pots in which a 50 μm mesh net allowed the physical separation of the mycorrhizal hyphae from the roots in one portion of the pot. An inorganic source of 15N was added to the hyphal compartment at the same time of the 13CO2 pulse labelling. One and seven days after pulse labelling, the plants were destructively harvested and the amount of the recently fixed carbon (C) and of the absorbed N was determined. 13C allocated to belowground organs such as roots and mycorrhizal hyphae accounted for an average of 10%, with 4.3% allocated to mycorrhizal hyphae within the first 24 hours after the pulse labelling. Mycorrhizae absorbed labelled inorganic nitrogen, of which almost 23% was retained in the fungal mycelium. The N uptake was linearly correlated with the 13C fixed by the plants suggesting a positive correlation between a plant photosynthetic rate and the hyphal absorption capacity.