Morphophysiological and biochemical responses of two grape cultivars to phosphorus deficiency and toxicity

Phosphorus (P) is a vital macronutrient for grapevine (Vitis vinifera L.); however, the physiological and biochemical mechanisms governing grapevine adaptation across varying P supply levels-from deficiency to toxicity-require further clarification. This study evaluated the morphophysiological, nutritional, and biochemical adaptations of two contrasting grapevine cultivars, 'Khalili' and 'Perlette', to varying P levels: 0 mM (deficiency), 2.5 mM (sufficiency), and 5 mM (excess/toxicity). Results demonstrated that vegetative growth parameters-including stem length, stem diameter, lateral shoot number, and shoot dry weight-peaked under P sufficiency (2.5 mM), whereas severe P deficiency and P excess significantly impaired shoot development. In contrast, root dry weight remained comparable between 2.5 and 5 mM P, resulting in a higher root-to-shoot ratio under P excess. Nutrient profiling revealed distinct tissue-specific partitioning: P supply promoted foliar P and N accumulation while altering root macronutrient status (N, P, K, Ca, Mg), but sharply reduced foliar Fe and Zn concentrations. In roots, elevated P suppressed Fe, Mn, and Cu accumulation while enhancing Zn uptake. Both P deficiency and excess triggered oxidative stress, evidenced by up-regulated activities of antioxidant enzymes (catalase, guaiacol peroxidase, and ascorbate peroxidase) in leaves and roots. Cultivar-specific responses were prominent: P deficiency induced substantial anthocyanin accumulation and higher leaf starch content in 'Khalili', whereas 'Perlette' maintained more stable ionic homeostasis under P excess. Overall, 2.5 mM P represents the physiological optimum for grapevine vegetative development, while both extreme deficiency and excess impair growth via distinct mineral imbalances and oxidative stress cascades.