Distribution of leaf mass per unit area and leaf nitrogen concentration determine partitioning of leaf nitrogen within tree canopies.

Distribution of leaf nitrogen with respect to leaf mass per unit area (M(a)), nitrogen per unit mass (N(m)) and nitrogen per unit area (N(a)) within peach (Prunus persica L.) tree canopies was studied in two field experiments. In one experiment, leaf light exposure and M(a) were measured on leaves from different canopy positions of peach trees subjected to five nitrogen (N) fertilization treatments. Leaf light exposure and M(a) were linearly related and the relationship was independent of N fertilization. In a subsequent experiment, N fertilizer was applied to previously unfertilized trees in midsummer, after shoot growth had terminated. Application of N fertilizer did not affect mean canopy M(a). Fertilization increased N(m) of all leaves throughout the canopy compared with non-fertilized trees. No significant relationship between N(m) and M(a) was found in either fertilized or control trees. There was a linear relationship between N(a) and M(a) and the slope of the relationship was increased by N fertilizer application. We conclude that distribution of N(a) in peach tree canopies is primarily a function of M(a) partitioning with light and N(m), which is related to soil N availability.