The Combined Effects of Salinity and Root Anoxia on Growth and Net Na+ and K+-accumulation in Zea mays Grown in Solution Culture

Abstract

The effects of excess salinity and oxygen deficiency on growth and solute relations in Zea mays L. cv. Pioneer 3906 were examined in greenhouse experiments. The roots of plants 14 d old growing in nutrient solution containing additions of NaCl in the range 1.0–200 mol m−3 were either exposed to a severe deficiency of O2 by bubbling with nitrogen gas (N2 treatment), or maintained with a supply of air (controls), for a period of 1–7 d. The threshold NaCl concentration resulting in appreciable inhibition of leaf extension, and shoot f. wt gain in controls was between 10 and 25 mol m−3. At 25 mol m−3 NaCl the ratio of Na+/K+ transported to shoots was about 20 times greater than in plants in 1.0 mol m−3 NaCl. The effect of addition of NaCl to the nutrient solution was to enhance Na+ movement but simultaneously depress the rate of K+ transport to shoots (per g f. wt roots). Interactions between NaCl levels and aeration treatment were shown by analyses of variance to be statistically significant for leaf extension, shoot and root f. wt gains, Na+ and K+ concentrations in shoots and roots. When roots were N2-treated, shoot and root growth were depressed, the effect of aeration treatment being greatest at NaCl concentrations of 50 mol m−3 or less. Additionally, N2-treatment greatly accelerated Na- transport to shoots while depressing K+ transport still further, so that at 10 mol m−3 NaCl the ratio Na+/K+ acquired by the shoots was 230 times greater than in controls. Over the concentration range 1.0 to 50 mol m−3 NaCl, the ratio Na+/K+ transported to shoots by anoxic roots increased by a factor of 860. Mechanisms controlling changes in solute flux to the shoot, and the significance in relation to plant tolerance of excess salts or oxygen deficiency are discussed.