Provenance variation in tolerance of Melaleuca cajuputi trees to interactive effects of aluminum and salt

Abstract

A future rise in sea level will expand areas of salt-affected acid sulfate soil, calling for studies on plant tolerance to combined aluminum (Al) and salt (NaCl) stress. We investigated random amplified polymorphic DNA (RAPD) profiles and tolerance to Al and NaCl alone and in combination in 14 Melaleuca cajuputi Powell 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 mostly by combined Al and NaCl stress and then by NaCl and least by Al. Moreover, Al enhanced the effect of NaCl on growth and vice versa. There were significant differences in plant growth among provenances under all treatments; however, positive relationships were found among Al tolerance, NaCl tolerance, and combined Al and NaCl tolerance. Provenance variation in stress tolerance increases with the increasing levels of stress effect. Furthermore, NaCl tolerance tended to have a positive relationship with osmotic potential. Leaf sap K concentration was decreased by NaCl and increased by Al; however, provenances that were more tolerant to NaCl tended to have lower K concentrations. RAPD analysis also revealed genetic variation among provenances. These results suggest that the low tolerance to combined Al and NaCl stress in M. cajuputi is largely due to low tolerance to NaCl and the effect of interaction between Al and NaCl. Provenance variation in stress tolerance was significant and could be partly explained by the variation in genetic material and the ability of plants to reduce ion excess stress in their shoots.