Abstract:

Land salinization-alkalization is a widespread environmental problem. The problem can be further classified, in terms of the salt characteristics, into salt-stress and alkali-stress. In fact, the destructive effects caused by alkali-stress is more serious than that by salt-stress. However, the information about alkali-stress is little up to the present. The resistance to salt and alkali stresses is stronger in Xiaobingmai (Triticum aestivum -Agropyron intermedium) than in other varieties of wheat. The cultivar Xiaobingmai 33 has been planted over some salt-alkalized areas, but its resistance to salt and alkali stresses is few studied yet. Therefore, Xiaobingmai 33 was chosen as the experimental materials to explore its physiological response to salt and alkali stresses and the difference between salt-stress and alkali-stress.The seedlings of Xiaobingmai 33 were treated for 12 days under five conditions of salt-stress and six conditions of alkali-stress, which were established by mixing NaCl and Na₂SO₄ or NaHCO₃ and Na₂CO₃ at 1:1 molar ratio respectively. The concentration range of treatments was from 60 to 300 mmol L^-1 for the salt-stress, and 30 to 180 mmol L^-1 for the alkali-stress. Six strain indices including relative growth rate (RGR), water content, malondialdehyde (MDA) content, electrolyte leakage rate, chlorophyll content, and carotenoid content, and the contents of five solute including Na+, K+, proline, betain and organic acid, were determined. The physiological responses of Xiaobingmai 33 to salt-stress and alkali-stress were analyzed and compared in order to further identify the difference of both stresses.
The results showed that the decrease extents of RGR and water content and the increase extents of MDA and electrolyte leakage rate under-alkali stress were greater than those under salt-stress with increasing stress intensity. The contents of chlorophyll and carotenoid didn’t change under salt stress, but decreased sharply under alkali-stress. Under both stresses, the contents of Na⁺ , proline, and betain increased, while K⁺ content decreased, and the changing degree under salt-stress was higher than that under alkali stress. In addition, organic acid content increased significantly under alkali-stress, but decreased slightly under salt-stress. In conclusion, all the strain responses to alkali-stress were more marked than those to salt-stress. The maximum concentration for Xiaobingmai 33 in resistance to salt-stress was 300 mmol L^-1, and that to alkali-stress was only 150 mmol L^-1 under the present experimental conditions. Alkali-stress caused great decrease of photosynthetic pigment content, which might be one of the reasons that the effect of alkali-stress was more severe than that of salt-stress. The accumulation of organic acids might be a special physiological mechanism of Xiaobingmai response to alkali-stress. The present study indicate that salt-stress and alkali-stress are two different stresses, not only in their effects on plant, but also in the response of plant to them.

Key words: Xiaobingmai (Triticum aestivum -Agropyron intermedium), Alkali-stress, Salt-stress, Physiological response