Nitrogen demand disparities and physiological responses in grapevine cultivars under contrasting nitrogen regimes

Nitrogen assimilation critically regulates plant developmental plasticity and metabolic homeostasis. Although intraspecific nitrogen demand variation influences agricultural efficiency, its systematic characterization in grapevines remains limited. This study elucidated cultivar-specific nitrogen responsiveness through Comparative growth-physiological analysis of two phenotypically distinct Vitis vinifera cultivars ('Red Globe' and 'Crimson Seedless') under five controlled nitrogen regimes (3.34, 6.68, 13.36, 20.04, and 26.72 mM). The findings indicated that nitrogen levels play a crucial role in regulating the growth and physiological processes of two grapevine cultivars. The 'Red Globe' demonstrated optimal growth at a nitrogen concentration of 20.04 mM, while the 'Crimson Seedless' reached its peak performance at 13.36 mM, reflecting a 33.3 % lower nitrogen requirement compared to 'Red Globe'. Both cultivars experienced growth inhibition and impaired physiological traits under conditions of both nitrogen deficiency and excess. At their respective optimal nitrogen concentrations, both cultivars accumulated significant biomass in aboveground tissues and roots, maintained elevated chlorophyll levels in leaves to maximize photosynthetic capacity, and enhanced protective enzyme activities (e.g. SOD, POD, CAT), along with osmolyte accumulation. These adaptations strengthened antioxidant defenses and sustained physiological functionality. Gene expression analysis revealed that key nitrogen metabolism genes in 'Crimson Seedless' (VvNR1/2, VvGDH, VvNiR) were upregulated with increasing nitrogen supply but were rapidly downregulated under conditions of nitrogen excess, indicating more rapid adaptive metabolic responses. Comparative analysis revealed that 'Crimson Seedless' exhibited heightened sensitivity to nitrogen, whereas 'Red Globe' showed greater tolerance to nitrogen variations. These findings offer significant insights for the precision management of nitrogen in grape cultivation.