Optimal nitrogen allocation controls tree responses to elevated CO2
Optimal nitrogen allocation controls tree responses to elevated CO2
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DOI：
10.1111/j.1469-8137.2007.02063.x
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发表时间：
2007-01-01
期刊：
影响因子：
9.4
通讯作者：
Franklin, Oskar
中科院分区：
文献类型：
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作者：
Franklin, Oskar
尽管有大量的实验数据，但对森林对二氧化碳浓度升高的反应的理解仍然有限。在此我表明，先前无法解释的生产力和叶面积反应的关键在于整株植物氮（N）分配与叶片光合作用之间的相互作用。一个通过优化叶面积指数（LAI）和植物氮来实现净生长最大化控制的简单树木生长模型，被用于分析幼龄、扩展以及郁闭、稳态冠层对二氧化碳的反应。这些反应仅对两个独立参数敏感，即单位叶氮的光合能力（a）和细根氮与叶氮的比率。该模型解释了在四个森林开放式空气二氧化碳富集（FACE）实验中观察到的光合作用、生产力和叶面积指数对二氧化碳的反应。除了在低叶面积指数时叶面积指数不敏感、光能利用效率提高以及在二氧化碳浓度升高时（由于单位面积叶氮减少导致的）光合下调，都通过对a和叶片量子效率的综合影响得到了解释。该模型弥合了对叶片水平和植株水平反应理解之间的差距，并为解释和关联结构（叶面积指数）和功能（净初级生产力（NPP）与总初级生产力（GPP）的比率、光能利用效率、光合下调）对二氧化碳浓度升高的反应提供了一个清晰的框架。
Despite the abundance of experimental data, understanding of forest responses to elevated CO2 is limited. Here I show that a key to previously unexplained production and leaf area responses lies in the interplay between whole-plant nitrogen (N) allocation and leaf photosynthesis.A simple tree growth model, controlled by net growth maximization through optimization of leaf area index (LAI) and plant N, is used to analyse CO2 responses in both young, expanding and closed, steady-state canopies. The responses are sensitive to only two independent parameters, the photosynthetic capacity per leaf N (a) and the fine-root N : leaf N ratio.The model explains observed CO2 responses of photosynthesis, production and LAI in four forest free air CO2 enrichment (FACE) experiments. Insensitivity of LAI except at low LAI, increase in light-use efficiency, and photosynthetic down-regulation (as a result of reduced leaf N per area) at elevated CO2 are all explained through the combined effects on a and leaf quantum efficiency.The model bridges the gap between the understanding of leaf-level and plant-level responses and provides a transparent framework for interpreting and linking structural (LAI) and functional (net primary production (NPP) : gross primary production (GPP) ratio, light-use efficiency, photosynthetic down-regulation) responses to elevated CO2.