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 Na 2 SO 4 or NaC1, and 0, 1, 3, or 10 Mm supplemental Ca 2+ in sand culture in the greenhouse. Greatest stomatal conductance (g s ) and net assimilation (A) occurred in unsalinized `Tifblue' plants not given additional Ca 2+ . Stomatal conductance, A, transpiration (E), and xylem water potential(Ψ)of `Tifblue' and `Sharpblue' plants were all lowered as salinity increased, and these effects were more pronounced with NaCl than with Na 2 SO 4 . 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 salinized with 100 m m Na + as Na 2 SO 4 , 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 Ca 2+ 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 Ψ w Ca 2+ 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 Ca 2+ to counter Cl - entry and toxicity. In contrast, additional Ca 2+ improved g s , A, Ψ w , and leaf chlorophyll content of `Tifblue' plants that received Na 2 SO 4 . For plants treated with 25 m m Na + as Na 2 SO 4 and 1 m m Ca 2+ , g s was 1.5 to 2.5 times higher than in plants without added Ca 2+ . Low (1 m m ) concentrations of Ca 2+ were more effective in ameliorating the effects of 100 m m Na + as Na 2 SO 4 . than were 3 or 10 m m Ca 2+ supplements, possibly because higher Ca 2+ concentrations damaged the metabolism of the calcifuge blueberry.