MAXIMIZATION OF DAILY CANOPY PHOTOSYNTHESIS : EFFECTS OF HERBIVORY ON OPTIMAL NITROGEN DISTRIBUTION
MAXIMIZATION OF DAILY CANOPY PHOTOSYNTHESIS : EFFECTS OF HERBIVORY ON OPTIMAL NITROGEN DISTRIBUTION
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日常冠层光合作用的最大化：草食对最佳氮分布的影响
DOI：
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发表时间：
1994
期刊：
影响因子：
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通讯作者：
B. Stockhoff
中科院分区：
文献类型：
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作者：
B. Stockhoff
最近的模型表明，随着光强的增加，单位面积上较高的叶片氮素浓度可以最大限度地提高氮素利用效率。因此，当氮素浓度接近冠层顶部时，冠层总光合作用最大。在前人工作的基础上，根据光、叶氮和叶片的分布建立了一个每日冠层光合作用的模型。模型表明，氮素的最佳分配主要取决于叶片的严重程度和位置。相对于在没有食草性的情况下最大限度地促进冠层光合作用的氮素分配，当草食动物取食冠层顶部的高氮叶或靠近冠层底部的低氮叶时，最优的氮素分配分别向更均匀的或偏斜的分布转移。这些结果表明，由于叶片损失通过增加剩余叶片的光照来平衡，植物的氮素分配模式应该取决于落叶的严重程度，以及损害是集中在冠层的顶部还是底部。此外，氮素分配对光合作用的关键重要性意味着，植物不一定要尽量减少叶面积对叶片的损失，而应该保护总氮素与叶面积的比率和氮素在冠层内的分配。作为植物防御理论的营养胁迫假说的推论，该模型表明，植物可能需要运输养分，以维持在草食后冠层中的最佳分配。该模型强调了这样一个观点，即当氮素在叶片中不均匀分布时，单靠叶面积损失不是光合作用能力丧失的不良指标。为了准确地评估对植物的损害，人们不仅必须考虑哪些资源已经被移走，而且必须考虑哪些资源仍然存在。
Abstract Recent models have shown that higher leaf nitrogen concentration per unit area maximizes nitrogen use efficiency with increasing light intensity. As a result, total canopy photosynthesis is maximized when nitrogen concentrations are higher towards the top of a canopy. Expanding upon this previous work, a model of daily canopy photosynthesis was constructed based on distributions of light, leaf nitrogen, and folivory. The model indicates that the optimal distribution of nitrogen depends significantly upon both the severity and location of folivory. Relative to nitrogen distributions that maximized daily canopy photosynthesis without herbivory, the optimal nitrogen distribution shifted towards either more uniform or skewed distributions when herbivores fed on high nitrogen foliage at the top of the canopy or on low nitrogen foliage towards the bottom of the canopy, respectively. These results suggest that, because foliar losses are balanced by increased irradiance of remaining leaves, plants' nitrogen allocation patterns should depend on how severe defoliation is and whether damage is concentrated towards the top or bottom of a canopy. Moreover, the critical importance of nitrogen distribution to photosynthesis implies that plants should not necessarily minimize loss of leaf area to folivores, but should protect the ratio of total nitrogen to leaf area and the distribution of nitrogen within the canopy. As a corollary to the nutrient stress hypothesis of plant defense theory, the model suggests that plants may need to translocate nutrients to maintain an optimal distribution in the canopy following herbivory. The model reinforces the point that leaf area loss alone is a poor indicator of loss of photosynthetic capacity when nitrogen is non-uniformly distributed among leaves. To accurately assess damage to a plant, one must consider not only what resources have been removed, but what resources remain.