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' s outhern 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 supplem ental Ca2+ in sand culture in the greenhouse. Greatest stomatal conduc tance (g(s)) and net assimilation (A) occurred in unsalinized 'Tifblue ' plants not given additional Ca2+. Stomatal conductance, A, transpira tion (E), and xylem water potential (PSI(w)) of 'Tifblue' and 'Sharpbl ue' plants were all lowered as salinity increased, and these effects w ere more pronounced with NaCl than with Na2SO4. After 63 days, for pla nts given 100 Mm Na+ as NaCl, g(s) and net assimilation rate were redu ced to only 10% of the unsalinized controls, while for plants satinize d with 100 mM Na+ as Na2SO4, g(s) and A were 35% and 43%, respectively , of unsalinized controls. Leaf necrosis was more extensive on 'Sharpb lue' plants given NaCl than on 'Tifblue' plants. Neither Ca2+ nor Natreatments led to severe chlorosis; reductions in leaf chlorophyll con tent were mainly due to necrosis. The Na+-induced reduction in gas exc hange was associated with negative PSI(w) Ca2+ deficiency, or a combin ation of these factors. Additional factors leading to inhibition of ga s exchange in NaCl- stressed plants include Cl- toxicity and leaf necr osis. Calcium supplements were unable to ameliorate NaCl damage in 'Ti fblue' or 'Sharpblue' plants, possibly because of the inability of Ca2 + to Counter Cl- entry and toxicity. In contrast, additional Ca2+ impr oved 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 add ed Ca2+. Low (1 mM) concentrations of Ca2+ were more effective in amel iorating 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.