A meta-analysis of leaf nitrogen distribution within plant canopies

Leaf N is generally highest in top leaves and decreases with depth in leaf canopies. Although such a gradient contributes to efficient use of canopy N for photosynthetic production, the gradient of leaf N is suboptimal in actual canopies.

Relationship between nitrogen distribution coefficients and light extinction coefficient (K_L). Full details Hikosaka et al. (2016)

Hikosaka et al. present a meta-analysis of the vertical gradient of leaf N which reveals that in most canopies except for wheat, the slope of the leaf N was half of the optimal slope.