Consequences of Micro- and Macronutrient Deficiencies on Physiological and Growth Metrics in Hydroponic ‘Thompson Seedless’ Grapevines

(1) Background: Mineral nutrient deficiencies are a major constraint on grapevine growth and productivity, yet the clear identification of deficiency symptoms and their physiological impacts remains challenging. (2) Methods: In this study, ‘Thompson Seedless’ grapevines were grown hydroponically under the controlled omission of ten essential nutrients (N, P, K, Ca, Mg, Fe, Mn, B, Zn, Cu) to assess their impact on growth, leaf morphology, chlorophyll content, photosynthesis, respiration, and tissue nutrient concentrations. (3) Results: Deficiencies in N, P, K, Mn, and B caused distinct leaf symptoms: nitrogen (N) deficiency led to pale leaves with bluish-green veins, phosphorus (P) deficiency caused yellowing in apical leaves followed by interveinal chlorosis, and potassium (K) deficiency induced pale yellow discoloration, curling, and rotting of the leaves. Manganese (Mn) and boron (B) deficiencies showed symptoms such as irregular leaf shapes and brittle, glossy leaves, respectively. These deficiencies resulted in reduced dry matter accumulation, decreased shoot length, and lower chlorophyll content. In contrast, iron (Fe) and copper (Cu) deficiencies had minimal effects, closely resembling those of the control conditions with only slight growth suppression. Notably, N, B, and Mg deficiencies led to significant reductions in Cu, Mg, B, and N levels, particularly evident through distinct symptoms in newly formed leaves. (4) Conclusions: Deficiencies in N, P, K, Mg, and B significantly affect grapevine growth, physiological processes, and nutritional quality. These findings emphasize the importance of maintaining balanced mineral nutrition for optimal grapevine health and productivity.