Fig. 3: Effect of exogenous ammonium on M. truncatula growth.

The effects of increasing the availability of soil ammonium on the growth rate of nodulated M. truncatula was examined. Simulations were run allowing either the N2-fixation efficiency to vary while the rate of nodulation remained constant at 2% (blue) or allowing the rate of nodulation to vary while the N2-fixation efficiency remained constant at 150 µmol h−1 (g nodule dry weight)−1 (red). The dashed lines indicate the maximal rate of plant growth with exogenous ammonium (upper) and the maximal rate of plant growth when relying on N2-fixation (lower).