Mn Toxicity Differentially Affects Physiological and Biochemical Features in Highbush Blueberry (Vaccinium corymbosum L.) Cultivars

Manganese (Mn) is an essential micronutrient for plants; however, in excess, it can have negative effects on their physiological and biochemical characteristics. We evaluate photosynthetic performance, antioxidant activity, and organic acid exudations to clarify the mechanisms involved in highbush blueberry (Vaccinium corymbosum L.) under Mn excess. One-year-old plants of V. corymbosum cultivars (Legacy, Brigitta, and Bluegold) were grown in hydroponic solution with 2, 10, 50, 250, 500, and 1000 μM of Mn treatments for 25 days. Plant growth as shoot and root biomass, Mn content, photosynthetic performance [photochemical efficiency of PSII, CO2 assimilation, and stomatal conductance (gs)], lipid peroxidation, radical scavenging activity, superoxide dismutase activity, and organic acid exudations were analyzed. Mn excess triggered detrimental effects in terms of plant growth, photochemical efficiency, and CO2 assimilation, as well as in biochemical features in V. corymbosum cultivars. Despite Legacy decreasing its photosynthesis, plant growth was maintained throughout the experiment; by contrast, Brigitta maintained photosynthesis and growth despite the decrease in stomatal conductance (gs). Meanwhile, Bluegold presented the lowest level in net photosynthesis and photochemical processes and an increase in lipid peroxidation. Oxalate and citrate were the most important organic acid anions in Legacy and Brigitta, gradually increasing their concentration with the enhancement of Mn doses. Our study demonstrated that Mn excess negatively and differently affects the physiological and biochemical features of V. corymbosum cultivars, with Legacy and Brigitta being Mn-resistant and Bluegold Mn-sensitive.