Fig. 2. Percentage of net photosynthesis allocated to nodulated roots of Pisum sativum expressed per unit of nodulated root biomass and plotted as a function of net C‐assimilation for two N treatments: N₂‐fixing plants (N₀ treatment) (open symbols), or plants supplied with nitrate (N₅ treatment) (closed symbols), at the vegetative (diamonds) and flowering (circles) stages. Symbols with a dot in the centre represent data from experiments conducted in 1999; all other data are from 2000.