Effects of Growing Wheat in Hypoxic Nutrient Solutions and of Subsequent Transfer to Aerated Solutions. II. Concentrations and Uptake of Nutrients and Sodium in Shoots and Roots

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We report on the effects of hypoxia (low O2 concentrations) in the nutrient solution on the net uptake of Cl-, N, P, K+ and Na+ by 26-30-day-old wheat plants (Triticum aestivum L.). Plants treated with hypoxia had been grown at 0.003 mol O2 m-3 for 10 days; four consecutive samplings were taken between 10 and 14 days to assess the uptake of nutrients. After the first sampling, one group of plants exposed to hypoxia was returned to aerated solutions containing 0.27 mol O2 m-3 . Seminal and crown roots grown in hypoxic solutions showed remarkably few differences in ion relations, despite the high porosity and the fast growth of the crown roots. The exception was with K+ /Na+; a decrease in this ratio due to growth in hypoxic solutions was more pronounced for seminal than for crown roots. Concentrations of elements in the shoots were nearly always lower for plants grown at 0.003 than for plants grown at 0.27 mol O2 m-3 ; the only exception was for Na+ which increased in plants grown in the hypoxic solutions. Comparisons with published critical nutrient concentrations indicate that decreased growth at 0.003 mol O2 m-3 was not due to reduced nutrition of the plants. For N, this conclusion is supported by higher concentrations of soluble amino acids in plants at 0.003 than at 0.27 mol O2 m-3 . The reduction in net transport to the shoots of N, P, Cl- and K+ was due to a combination of decreases in root /shoot ratio and an inhibition of ion uptake per unit root weight. This inhibition was not due to permanent damage as it was reversible. A rapid restoration of concentrations of N, P, Cl- and K+ in the shoot upon transfer from 0.003 to 0.27 mol O2 m-3 was attributed to a combination of higher net rates of ion uptake by the roots compared with continuously aerated plants and a rapid expansion of the root system.