Abstract
Nitrogen deficit affects both crop production and composition, particularly in crops requiring an optimal fruit N content for aroma development. The adaptation of cultural practices to improve N use efficiency (NUE) (i.e. N uptake, assimilation and partitioning) is a priority for the sustainable production of high-quality crops. A trial was set on potted grapevines (Vitis vinifera L. cv. Chasselas) to investigate the potential of crop limitation (via bunch thinning) to control plant NUE and ultimately fruit N composition at harvest. A large crop load gradient was imposed by bunch thinning (0.5-2.5 kg m-2) and N traceability in the plant was realised with an isotope-labelling method (10 atom % 15N foliar urea). The results indicate that the mobilisation of root reserves plays a major role in the balance of fruit N content. Fertiliser N uptake and assimilation appeared to be strongly stimulated by high-yielding conditions. Fertilisation largely contributed to fulfilling the high fruit N demand while limiting the mobilisation of root reserves under high yield conditions. Plants were able to modulate root N reserve mobilisation and fertiliser N uptake in function of the crop load, thus maintaining a uniform N concentration in fruits. However, the fruit free amino N profile was modified, which potentially altered the fruit aromas. These findings highlight the great capacity of plants to adapt their N metabolism to constraints, crop thinning in this case. This confirms the possibility of monitoring NUE by adapting cultural practices.
Highlights
Fruit composition, though partly determined by genotype and uncontrolled environmental conditions, can be managed to some extent through the optimisation of agricultural practices, such as vineyard floor management, fertilisation, canopy management and crop thinning, before and during fruit development (Masclaux-Daubresse et al 2010; Sweetman et al 2014; Alem et al 2019)
The leaf : fruit ratio varied from a minimum of 0.5 to a maximum of 2.4 m2 kgÀ1, depending on the crop load
Crop load was manually controlled by bunch thinning and urea was applied late in the season when the canopy was already developed
Summary
Though partly determined by genotype and uncontrolled environmental conditions, can be managed to some extent through the optimisation of agricultural practices, such as vineyard floor management, fertilisation, canopy management and crop thinning, before and during fruit development (Masclaux-Daubresse et al 2010; Sweetman et al 2014; Alem et al 2019). It is still unclear how crop load influences N accumulation in fruits, even though N is essential for fruitfulness (number of bunches per shoot) and aroma development Several studies have explained the impact of crop thinning on fruit composition, considering the leaf : fruit ratio as an indicator of balanced plants
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