Arbuscular mycorrhizal contribution to nitrogen uptake of grapevines

Abstract

The role of arbuscular mycorrhizal fungi (AMF) in supporting tree nutrition has been recognized for many species, including grapes. This study aimed at determining whether AMF contribute to nitrogen (N) uptake by grapevines using 15N-enriched fertilizer to follow N transfer from the soil to the plant. Grapevines ['Nero'/'SO4'], grown in sand for 10 weeks, were divided into three fertilization treatments: (1) unlabeled NH4NO3; (2) 15NH415NO3 provided to root; (3) 15NH415NO3 provided to hyphae. The latter was obtained by splitting the pots in two compartments by a net impenetrable to roots, and adding the fertilizer only where AMF hyphae could develop. The vines were excavated and dry matter, total N and 15N concentration of each organ determined. Root AMF colonization (RLC) was evaluated on fresh roots. The nitrogen derived from fertilizer (Ndff) was calculated from the excess of 15N respect to its natural abundance.
Total biomass growth (~37 g/vine) and RLC (38 % on average) were not statistically different among the three treatments. 15N was mostly allocated to roots, shoots and leaves, while trunks were only barely enriched. The vines receiving N directly to roots had higher N concentration and total N than vines relying on AMF, however the amount of Ndff, roughly 500 µg·vine-1, was not different between the two treatments. These results indicate that vines growing in the compartmentalized pots might have had an initial shortage of N due to not fully developed AMF. Once the hyphal compartment was colonized, AMF contributed to N translocation to vines, as demonstrated by the same amount of Ndff found in the two treatments. Although preliminary, this study demonstrates the potentially important role of AMF to mineral nitrogen nutrition of grapevines and calls for further studies in pot and in the field.