Improving NaCl resistance of red-osier dogwood: role of CaCl2 and CaSO4

The influence of Ca2+ salts on the resistance of red-osier dogwood (Cornus sericea) seedlings to salinity was investigated. Red-osier dogwood seedlings were exposed to 5 and 10 mM of CaCl2 or CaSO4 in the presence or absence of 50 mM NaCl for 40 days in a controlled environment. Seedlings exposed to CaCl2 and CaSO4 recovered from NaCl-induced transpiration reduction after 20 days at a concentration of 10 mM and after 30 days at a concentration of 5 mM; while in absence of additional Ca2+, the seedlings recovered only after 40 days. Addition of 10 mM Ca2+ to NaCl treatment also limited the accumulation of proline in leaf tissues and caused an increase in leaf and lateral shoot K+ content. These results suggest that 10 mM Ca2+ could alleviate, at least in part, the osmotic effect of NaCl on red-osier dogwood via control of stomatal closure. On the other hand, ion analysis showed that Ca2+ addition was able to reduce the NaCl-induced Na+ concentration only in stem tissues suggesting that Ca2+ had only a limited effect on the ionic stress. The present study also showed an unexpected NaCl-induced increase in Ca2+ content of leaves, lateral shoots and stems that was not observed in our previous hydroponics experiments and seems to be more characteristic of plants growing on sandy soils.