The Interaction among Provenances of Melaleuca leucadendra (Weeping Paperbark), Salt, and Aluminum
The expansion in salt-affected acid sulfate soil areas induced by the rise in sea level calls for studies on plant tolerance to combined aluminum (Al) and salt (NaCl) stress. We investigated the difference in tolerance to Al and NaCl alone and in combination among 16 Melaleuca leucadendra (L.) L. provenances. Two-month-old seedlings were grown with or without 10 mM Al and/or 50 mM NaCl at pH 3.8 for 3 months. Plant growth was reduced most by combined Al and NaCl stress and then by NaCl and least by Al, and provenance variation in stress tolerance increased with an increase in the level of the stress effect. Al and NaCl enhanced each other's effects in nine provenances, but they alleviated each other's effects in two provenances. There were significant differences in plant growth among provenances in every treatment; however, positive relationships were found among Al tolerance, NaCl tolerance, and combination tolerance. Combined Al and NaCl stress greatly increased Na concentration, whereas it decreased K concentration in leaf sap. Tolerance to combination stress tended to have negative relationships with both stress-induced reduction in leaf osmotic potential and leaf K concentration among provenances, suggesting that provenance variability in tolerance to combined Al and NaCl stress is partly due to differences in the ability to limit ionic stress through an adjustment in K uptake.
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