Effect of Nitrate Concentration on the Root: Shoot Ratio in Dactylis glomerata L. and on the Kinetics of Growth in the Vegetative Phase

The vegetative growth of Dactylis glomerata L. in sand was studied under controlled light, temperature, and nutritional conditions. Plants were daily supplied with three nutrient solutions of different nitrate concentrations (10−2, 10−3 and 2 × 10−4 mol I−1). For each concentration, growth obeyed an exponential law between the fourth and seventh weeks after sowing. The time constant of the exponential was the same for the shoot as for the root, and showed no significant variation with nitrate concentration. The kinetic results and the strong dependence of the root: shoot ratio on nitrate concentration are discussed on the basis of Thornley's model. Hypothesizing that the molecular mechanisms of nitrate absorption are independent of the nitrate concentration of the nutrient solution, we derived a relationship between the root: shoot ratio and nitrate concentration. This relationship was found to be compatible with the experimental results.