Effects of root temperature and nitrogen form on magnesium uptake and translocation by wheat seedlings

Low concentrations and low bioavailability of Mg in winter wheat forage have been related to grass tetany, a metabolic disorder of grazing ruminants caused by Mg deficiency in the blood serum. To investigate the effects of root temperature, N form, and Mg supply on Mg uptake and translocation by winter wheat (Triticum aestivum L. 'Centurk'), seedlings were grown in nutrient solution with three root-zone temperatures (RZT) (10, 15, or 20 °C), three N forms (NH4:NO3 in mM 10:0, 5:5, or 0:10), and two Mg levels (0.4 or 4 mM). Increasing the RZT increased Mg uptake rates of seedlings less than 30 days old, but decreased Mg uptake rates for plants more than 30 days old. Magnesium uptake rates were significantly higher for plants supplied only NO3 than for plants supplied only NH4. However, increasing the proportion of NO3 significantly decreased net Mg translocation. Consequently, shoot Mg concentrations at the low Mg level were significantly decreased by increasing the proportion of NO3. As was found for net Mg translocation, net K translocation was significantly decreased by increasing the proportion of NO3. However, net Ca translocation was not significantly affected by the N form. Correlation analysis showed that net Mg translocation was negatively correlated with root K concentrations. The absolute values of the correlation coefficients were increased as the medians of root K concentrations increased. The results indicate that factors inducing an increase in root K concentrations may result in a depression of net Mg translocation from roots to shoots.