Nitrogen and carbohydrate reserves in the grapevine (Vitis vinifera L. 'Chasselas'): the influence of the leaf to fruit ratio
Seasonal patterns of total organic nitrogen (N) and total non-structural carbohydrate (TNC) concentrations in relation to the leaf-fruit ratio (source-sink) were measured over three years at different grapevine phenological stages in one- and two-year-old canes, trunks and roots of the cultivar 'Chasselas' (Vitis vinifera L.). The highest N and TNC concentrations were observed during the period from dormancy until budbreak. A decrease in the N and TNC reserves was measured in the different organs (canes, trunks and roots) from budbreak, reaching minimum values around flowering, except for the N concentration in the roots, which was lowest during the period between bunch closure and veraison. N storage was highest in the roots and occurred from veraison until leaf fall. The N concentration in the trunks and canes represented approximately half of that measured in the roots. TNCs accumulated preferentially in the roots and also in the trunks and canes during the growing season. The leaf area per vine (or canopy height) and yield both influenced the N concentration in the roots. High yield and low leaf area per vine decreased the N concentration in the roots. The leaf-fruit ratio, expressed as the "light-exposed leaf area per kg fruit", substantially influenced the N and TNC concentrations in the roots at harvest. The highest N and TNC concentrations in the roots were obtained when the leaf-fruit ratio approached 2.0 m2 of light-exposed leaf area per kg fruit.
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