Stagnant treatment plus salinity reduced growth more than salinity alone, or stagnant alone, but some accessions of H. marinum were still relatively tolerant of these combined stresses, maintaining Na(+) and Cl(-) 'exclusion' even in an O(2)-deficient, saline rooting medium.
Communities of Tecticornia on the margins of ephemeral salt lakes in Australia often exhibit species zonation, such as at Hannan Lake (Western Australia) where Tecticornia indica subsp. bidens (Nees) K.A.Sheph. and Paul G.Wilson occupies the less saline dune habitat on lake margins and Tecticornia pergranulata (J.M.Black) K.A.Sheph. and Paul G.Wilson subsp. pergranulata occupies both the dunes and the more saline and moist lake playa. Here we tested the hypothesis that these two species differ in tolerance to extreme salinity. Plants were grown in drained sand cultures with treatments of 10–2000 mM NaCl for 85 days. Both species were highly salt tolerant, maintaining growth at treatments of up to 2000 mM NaCl, although the death of two replicates of T. indica at 2000 mM NaCl suggests this salinity is close to the species tolerance limit. Both Tecticornia species maintained a favourable gradient in tissue water potential via osmotic adjustment as external salinity increased, also with reduced tissue water content at very high external salinity. Regulated accumulation of Na+ and Cl–, maintenance of net K+ to Na+ selectivity, high tissue concentrations of glycinebetaine and presumed cellular solute compartmentation, would have contributed to salt tolerance. The growth rate of T. pergranulata was 11–29% higher than T. indica suggesting, in addition to these moderate differences in salinity tolerance, other factors are likely to contribute to species zonation at salt lakes. The higher water use efficiency of the C4 T. indica compared with the C3 T. pergranulata may provide an advantage in the drier dune habitat on salt lake margins. An additional experiment confirmed the hypothesis that survival of T. pergranulata seedlings is enhanced by the duration of reduced salinity after germination, as would occur following significant rainfall, as older seedlings maintained higher growth rates during subsequent increases in salinity.
Background and aims Tecticornia species are stemsucculent, perennial halophytes (sub-family Salicornioideae; Chenopodiaceae) that inhabit saline areas including the margins of ephemeral salt lakes in Australia. Based on zonation observed at salt lakes, species were hypothesised to differ in tolerances to salinity and/or waterlogging. Methods Three Tecticornia species were grown in sub-irrigated or waterlogged sand culture with treatments from 10 to 800 mM NaCl, for 60 d in a glasshouse. Growth, tissue solutes, root porosity, root radial O 2 loss, and ethanol production, were assessed. Results The three species were salt tolerant; at 800 mM NaCl shoot RGR (ash-free) was reduced by 9% in T. indica, 22% in T. pergranulata and 39% in T. mellaria. Na + and Cl − were the predominant osmotica in succulent stem tissues. Glycinebetaine was a major organic solute. T. pergranulata and T. indica were waterlogging tolerant; shoot RGR was reduced by at most 29% irrespective of salinity. Waterlogging tolerance in T. mellaria was variable (shoot RGR 8%-56% of controls) and some individuals died. T. pergranulata formed adventitious roots with aerenchyma, but the two other species did not. Anoxic tips of lateral roots produced ethanol. Conclusion The three Tecticornia species are salt tolerant. T. pergranulata is also waterlogging tolerant and formed adventitious roots containing aerenchyma, traits consistent with growth on mud flats of salt lakes. T. indica was unexpectedly tolerant of waterlogging, whereas T. mellaria was less tolerant. Future work is needed to evaluate tolerances of inundation (i.e. submergence) and to higher salinity treatments.
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