Nitrogen and phosphorus allocation in leaves, twigs, and fine roots across 49 temperate, subtropical and tropical tree species: a hierarchical pattern

摘要

1. Hierarchical branching is a fundamental feature of trees. Understanding how tree architecture is linked to tissue nutrient concentrations, metabolic rates, and life cycles is important for predicting ecosystem processes such as respiration, module turnover, and organic matter decomposition. 2. Here, we examined branch order-nutrient relationships in above- and belowground tree branching systems by analysing nitrogen (N), phosphorus (P), and N : P ratio in leaves, the first three orders of twigs, and the first five orders of roots in 49 tree species, including 21 temperate angiosperm species, six temperate gymnosperm species, and 22 subtropical-tropical angiosperm species. 3. Tissue [N] and [P] declined linearly with increasing twig and root orders across all species. The slope of the linear regression between root order and root [N] was the same between temperate and subtropical-tropical angiosperms, but steeper in angiosperms than gymnosperms. In contrast, root order-[P] relationship differed between biomes but not between phylogenetic groups, probably due to the significantly lower P availability in subtropical-tropical soils. Additionally, the magnitude of change in tissue [N] and [P] between successive shoot and root branch orders was not constant across branching levels. Among all fine root orders, first order root tips had [N], [P], and N : P ratio most similar to those of leaves. 4. These results demonstrate that there is a general inverse order-nutrient relationship in above- and belowground modules, though specific patterns of this relationship differed between N and P, and between species groups. Moreover, among all root orders within the fine root guild, root tips are the best parallels of leaves in nutrient concentrations. The order-nutrient relationships presented here advances our understanding of functional module construction in trees, and provide a basis for modelling tissue chemistry-regulated processes such as respiration and decomposition in forest ecosystems.