Response to Salt and Waterlogging Stress of Ten Taxa of Acacia Selected From Naturally Saline Areas of Western Australia

Abstract

Ten taxa of Acacia were selected from areas of moderate to high soil salinity (electrical conductivities of saturated soil paste extracts (EC_e) between 1000 mS m-^-1 and 4800 mS m^-1 at 50-600 mm depth) and sodicity to test the tolerance of young, symbiotic plants to increasing levels of salinity both with and without waterlogging. Nodulated plants, 3 months old, were grown in glasshouse experiments which consisted of four treatments: non-saline drained control (12 weeks); saline drained (12 weeks); non-saline waterlogged (5 weeks); and saline waterlogged (5 weeks).

Acacia cyclops, A. brumalis, A. redolens (Ravensthorpe) and A. aff. lineolata had 100% survival after 12 weeks irrigation with saline solution (final EC_w = 9500 mS m^-1). Generally, the species tested were sensitive to waterlogging with A. patagiata, A. cyclops and A. brumalis being the most sensitive, having 19-44% mortality with no salt in the solution. The combined treatment of salt and waterlogging greatly increased the mortality of plants, with four species having > 70% dead after 5 weeks treatment (EC_w = 3900 mS m^-1). A. aff. lineolata and A. mutabilis subsp. ,stipulifera were highly tolerant of salt plus waterlogging, with 100% and 96% survival respectively.

In salt plus waterlogged treatments, Na⁺ concentration in phyllodes of all taxa exceeded (0.37-2.13 mmol g^-1 dry wt) that taken up by plants in freely drained salt treatments (0.03-0.42 mmol g^-1 dry wt). Taxa with the slowest rates of growth tended to accumulate the highest concentrations of Na⁺ in the uppermost phyllodes.

Provenances of A. redolens and A. patagiata collected from sites of high soil salinity (EC_e > 2200 mS m^-1) had less than half the Na⁺ concentration in uppermost phyllodes (0.22 mmol ^-1 dry wt) at the termination of the salt treatment, compared with provenances of the same species collected from moderately saline areas (EC_e = 1100 mS m^-1). This indicates that Acacia provenances collected from the most saline sites had greater potential to survive high levels of external salinity in the longer term than those from less saline sites.