Root: shoot ratio as a balance between nitrogen productivity and photosynthesis

Abstract It is shown how root : shoot ratios can be derived from two plant characteristics, (i) the nitrogen productivity (amount of biomass produced per unit of nitrogen in the biomass and per unit of time) and (ii) the relationship between photo‐synthetic rate and internal nitrogen concentration. Derived root: shoot ratios are compared with experimental data for seedlings of seven tree species grown with stable internal nitrogen concentrations. Agreement is good but more exact knowledge of the relationship between nutrient status and photosynthesis is needed. It is shown that a formula derived for the root: shoot ratio can also be applied under non‐steady‐state conditions.