GAS-EXCHANGE AND CHLOROPHYLL CONTENT OF TIFBLUE RABBITEYE AND SHARPBLUE SOUTHERN HIGHBUSH BLUEBERRY EXPOSED TO SALINITY AND SUPPLEMENTAL CALCIUM

Tifblue' rabbiteye blueberry (Vaccinium ashei Reade) and 'Sharpblue' southern highbush blueberry (primarily V. corymbosum) were treated with 0, 25, or 100 Mm Na+ as Na2SO4 or NaCl, and 0, 1, 3, or 10 Mm supplemental Ca2+ in sand culture in the greenhouse. Greatest stomatal conductance (g(s)) and net assimilation (A) occurred in unsalinized 'Tifblue' plants not given additional Ca2+. Stomatal conductance, A, transpiration (E), and xylem water potential (PSI(w)) of 'Tifblue' and 'Sharpblue' plants were all lowered as salinity increased, and these effects were more pronounced with NaCl than with Na2SO4. After 63 days, for plants given 100 Mm Na+ as NaCl, g(s) and net assimilation rate were reduced to only 10% of the unsalinized controls, while for plants satinized with 100 mM Na+ as Na2SO4, g(s) and A were 35% and 43%, respectively, of unsalinized controls. Leaf necrosis was more extensive on 'Sharpblue' plants given NaCl than on 'Tifblue' plants. Neither Ca2+ nor Na+ treatments led to severe chlorosis; reductions in leaf chlorophyll content were mainly due to necrosis. The Na+-induced reduction in gas exchange was associated with negative PSI(w) Ca2+ deficiency, or a combination of these factors. Additional factors leading to inhibition of gas exchange in NaCl- stressed plants include Cl- toxicity and leaf necrosis. Calcium supplements were unable to ameliorate NaCl damage in 'Tifblue' or 'Sharpblue' plants, possibly because of the inability of Ca2+ to Counter Cl- entry and toxicity. In contrast, additional Ca2+ improved g(s) A, PSI(w), and leaf chlorophyll content of 'Tifblue' plants that received Na2SO4. For plants treated with 25 mm Na+ as Na2SO4 and 1 mm Ca2+, g(s) was 1.5 to 2.5 times higher than in plants without added Ca2+. Low (1 mM) concentrations of Ca2+ were more effective in ameliorating the effects of 100 mm Na+ as Na2SO4 than were 3 or 10 mM Ca2+ supplements, possibly because higher Ca2+ concentrations damaged the metabolism of the calcifuge blueberry.