title: New insights into carbon allocation by trees from the hypothesis that annual wood production is maximized.
abstract: Allocation of carbon (C) between tree components (leaves, fine roots and woody structures) is an important determinant of terrestrial C sequestration. Yet, because the mechanisms underlying C allocation are poorly understood, it is a weak link in current earth-system models. We obtain new theoretical insights into C allocation from the hypothesis (MaxW) that annual wood production is maximized. MaxW is implemented using a model of tree C and nitrogen (N) balance with a vertically resolved canopy and root system for stands of Norway spruce (Picea abies). MaxW predicts optimal vertical profiles of leaf N and root biomass, optimal canopy leaf area index and rooting depth, and the associated optimal pattern of C allocation. Key insights include a predicted optimal C-N functional balance between leaves at the base of the canopy and the deepest roots, according to which the net C export from basal leaves is just sufficient to grow the basal roots required to meet their N requirement. MaxW links the traits of basal leaves and roots to whole-tree C and N uptake, and unifies two previous optimization hypotheses (maximum gross primary production, maximum N uptake) that have been applied independently to canopies and root systems.
authors.affiliation: School of Biological, Earth and Environmental Sciences, The University of New South Wales, Sydney, NSW, 2052, Australia.
authors.forename: Ross E
authors.initials: RE
authors.lastname: McMurtrie
authors.affiliation: Research School of Biology, The Australian National University, Canberra, ACT, 0200, Australia.
authors.forename: Roderick C
authors.initials: RC
authors.lastname: Dewar
mesh_terms: D002244:Carbon / Q000378:metabolism*; D008954:Models, Biological; D009584:Nitrogen / Q000378:metabolism; D010788:Photosynthesis; D028222:Picea / Q000254:growth & development* / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D014197:Trees / Q000254:growth & development* / Q000378:metabolism*; D014934:Wood / Q000254:growth & development*
chemical_list: D002244:Carbon; D009584:Nitrogen
keywords: canopy photosynthesis; gross primary production; leaf area index; maximum wood production; optimization model; root nitrogen uptake; rooting depth; tree carbon allocation