Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, 08544, USA.
Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, NH, 03824, USA.
New Phytol. 2013 Oct;200(1):112-121. doi: 10.1111/nph.12353. Epub 2013 Jun 6.
Leaf nitrogen content (δ) coordinates with total canopy N and leaf area index (LAI) to maximize whole-crown carbon (C) gain, but the constraints and contributions of within-species plasticity to this phenomenon are poorly understood. Here, we introduce a game theoretic, physiologically based community model of height-structured competition between late-successional tree species. Species are constrained by an increasing, but saturating, relationship between photosynthesis and leaf N per unit leaf area. Higher saturating rates carry higher fixed costs. For a given whole-crown N content, a C gain-maximizing compromise exists between δ and LAI. With greater whole-crown N, both δ and LAI increase within species. However, a shift in community composition caused by reduced understory light at high soil N availability (which competitively favors species with low leaf costs and consequent low optimal δ) counteracts the within-species response, such that community-level δ changes little with soil N availability. These model predictions provide a new explanation for the changes in leaf N per mass observed in data from three dominant broadleaf species in temperate deciduous forests of New England. Attempts to understand large-scale patterns in vegetation often omit competitive interactions and intraspecific plasticity, but here both are essential to an understanding of ecosystem-level patterns.
叶片氮含量（δ）与总冠层 N 和叶面积指数（LAI）协调，以最大限度地提高全冠碳（C）增益，但物种内可塑性对这种现象的限制和贡献仍知之甚少。在这里，我们引入了一个基于生理的、具有游戏理论基础的物种间竞争的社区模型，该模型考虑了高度结构的竞争。物种受到光合作用和单位叶面积叶片氮之间的正相关但饱和关系的限制。较高的饱和率具有较高的固定成本。对于给定的全冠 N 含量，δ 和 LAI 之间存在 C 增益最大化的权衡。随着全冠 N 的增加，δ 和 LAI 在物种内都增加。然而，在高土壤 N 供应下，底层光照减少导致群落组成发生变化（这有利于具有低叶片成本和相应低最佳δ 的物种竞争），抵消了物种内的响应，使得群落水平的δ 变化不大土壤 N 供应。这些模型预测为新英格兰温带落叶林三种主要阔叶树种数据中观察到的叶片质量氮变化提供了新的解释。试图理解植被的大尺度模式往往忽略了竞争相互作用和种内可塑性，但在这里，这两者对于理解生态系统水平的模式都是必不可少的。
