Growth and magnesium uptake of tall fescue clones with varying root diameters

A cool season perennial grass with a root system capable of penetrating hardpans and which can accumulate adequate Mg to prevent deficiencies in forage is needed in the Coastal Plain region. A greenhouse experiment was conducted to determine the effects of magnesium (Mg) concentration in nutrient solution and root diameter on Mg uptake and growth of tall fescue (Festuca arundinacea Schreb.). Propagules of two fescue clones with large root diameter (LDR >1 mm), two clones with small root diameter (SDR <0.8 mm), and a single clone from 'Kentucky 31' (Ky-31) were transferred into 12-liter tanks containing Mg concentrations of 3, 21, 42, 125, 250, and 500 μM as MgSO4 and grown for 39 or 70 days. Leaf Mg concentration was increased linearly with Mg solution concentration in LDR clones for a 39-day growth period (Harvest 1), but increased according to a cubic equation in the SDR clones and the Ky-31. Predicted leaf Mg concentration as a function of solution Mg followed a cubic equation for a 70-day growth period (Harvest 2) in all clones. Predicted root Mg concentration was linearly related to Mg solution concentration for the LDR clones and the Ky-31, but followed a cubic equation for the SDR clones for the first growth period. For the second growth period, the root Mg concentration of the SDR clones and the Ky-31 was increased linearly, while the LDR clones followed a quadratic equation. Magnesium uptake followed a cubic equation with Mg solution concentration for both growth periods on all tall fescue clones. This nonlinear variation of Mg uptake and plant Mg concentration with respect to solution Mg concentration strongly suggests that a dual uptake mechanism might have been present in tall fescue clones. Root volume was greater in the SDR than LDR clones or Ky-31 for both growth periods. The Ky-31 had the greatest leaf and root dry weight for both growth periods, while the LDR clones had the lowest.