Monday, 10 July 2006

Toxicity of Na+ and Cl- to Wheat and Chickpea.

Anna R. Sheldon1, Ram C. Dalal2, and Neal W. Menzies1. (1) The University of Queensland, School of Land and Food Sciences, St Lucia, Brisbane, Australia, (2) Department of Natural Resources & Mines, 80 Meiers Rd, Indooroopilly, Brisbane, Australia

Exposure to elevated levels of NaCl is known to have a detrimental effect on the growth of most plants. The effect of NaCl salinity, is a combination of toxicity of Na+ and/or Cl- ions, and an osmotic effect which reduces the plants ability to take up water. Isolating the mechanisms of salinity, and how they combine to effect growth of various plant species, is an important step in the management of agriculture in saline environments. Solution culture experiments were conducted to examine Na+ and Cl- toxicity to wheat (Triticum aestivum L.) ‘Kennedy' and chickpea (Cicer arietinum L.) ‘Jimbour'. In order to separate the osmotic effect from the toxic effects of Na+ and/or Cl-, a treatment of mixed ions was compared with a treatment containing a high concentration of either Na+ or Cl-. The mixed ion treatment contained Na+, K+, Ca2+, Mg2+, Cl-, NO3-, and SO42-. To achieve the ion toxicity treatments, either the cation or anion component of the mixed ion treatment was replaced with Na+ or Cl-. Each treatment also contained a complete basal nutrient solution to ensure that no nutrient deficiencies occurred. Wheat was not susceptible to a specific toxicity of Cl-, as there was no significant difference (P > 0.05) between the growth reductions that occurred in the mixed anion and Cl treatments. However, a significant (P < 0.05) growth reduction was observed for chickpea in the response to Cl-. Dry weight of both wheat and chickpea was significantly (P < 0.05) reduced in response to Na+, compared to the mixed cations. The magnitude of the growth reduction for chickpea indicated that Cl- had a more detrimental effect on yield than Na+. Dry matter production by wheat showed a linear decrease as the Na+ concentration increased. A small additional growth reduction occurred due to the osmotic stress of other ions when the total solution concentration was high. Chickpea was also sensitive to Na+, though less sensitive than to Cl-, but the presence of other cations or anions in solution produced an ameliorative effect on these toxicities, rather than an additional osmotic effect. In general, chickpea was more sensitive to Na+ and Cl- than wheat, and accumulated higher concentrations of both ions in the plant tissues. The results of this experiment indicate that chickpea is an unsuitable crop for saline sites, and that growth reductions may occur even at slightly elevated levels of Cl-. Wheat however, is more tolerant and may grow well in moderately saline conditions, especially if a mixture of salts is present, though sodic sites should be avoided.

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