Carbon and nitrogen partitioning in either fruiting or non‐fruiting grapevines: effects of nitrogen limitation before and after veraison

Fruit effects on carbon (C) balance between reproductive and vegetative growth, and between shoots and roots, were studied under low versus high nitrogen (N) availability before and after veraison. Fruiting vines were compared with non‐fruiting vines, and N was supplied at either a low or high rate, and either continuously or as a split application before and after veraison. In non‐fruiting grapevines, leaf growth was greatly affected by N supply, but root growth was little affected. Low N supply before veraison favoured berry development, whereas after veraison enlarging fruits were disadvantaged by low N supply. Fruit growth was highly competitive with root growth, particularly before veraison, when N supply was low. Whole plant C and N accumulation rates were lower in fruiting plants. Berry amino acid content was influenced by all combinations of N treatments. Overall, fruit development was favoured by ensuring a low N supply rate before veraison, but this occurred at the expense of root growth as well as C and N uptake by the grapevines. After veraison, fruit can express a high sink strength if N is made available, probably because photosynthetic activity increases. These results provide new insights into how N may be managed in order to control grapevine C partitioning, to encourage berry development, and to sustain overall C and N uptake by grapevines.