Ackerly David
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA, , , , , , US.
Oecologia. 1999 May;119(3):300-310. doi: 10.1007/s004420050790.
A simple model of shoot-level carbon gain is presented addressing the optimal number and life span of leaves in relation to alternative optimality criteria: (1) maximizing carbon export from the shoot, or (2) maximizing the rate of leaf production at the shoot tip. Additionally, the processes that cause declining assimilation with leaf age are considered in relation to (1) leaf position on the shoot (e.g., self-shading) versus (2) leaf age per se. Using these alternative scenarios, only a model based on position-dependent assimilation and maximization of leaf production rates resulted in quantitative predictions for all aspects of leaf dynamics on the shoot (i.e., leaf number, life span, and birth rate), while other approaches predicted that one or more parameters would be infinite. This formulation of the model also predicted that leaves should be maintained on the shoot until the diurnal carbon balance declines to zero, in contrast with other scenarios which predict that leaves should be shed while maintaining a positive carbon balance. Predictions of the model were supported by the results of a field study of carbon gain and leaf dynamics in saplings of three species of tropical pioneer trees (Carica papaya, Cecropia obtusifolia, and Hampea nutricia) which differ in the number of leaves per shoot. The results illustrate that in these fast-growing plants, leaf production and height growth may be more appropriate measures of performance than net carbon export from the shoot, and suggest that leaf senescence is primarily a function of the position of a leaf within the canopy, rather than its chronological age.
本文提出了一个简单的地上部碳获取模型，该模型针对叶片的最佳数量和寿命，探讨了与不同最优性标准相关的问题：（1）最大化地上部的碳输出，或（2）最大化茎尖叶片的产生速率。此外，还考虑了导致叶片同化随年龄下降的过程，这些过程与以下两个方面有关：（1）叶片在茎上的位置（例如，自我遮荫）与（2）叶片本身的年龄。使用这些不同的情景，只有基于位置依赖性同化和叶片产生速率最大化的模型，才能对茎上叶片动态的所有方面（即叶片数量、寿命和出生率）做出定量预测，而其他方法预测一个或多个参数将是无限的。该模型的这种表述还预测，叶片应保留在茎上，直到昼夜碳平衡降至零，这与其他情景相反，其他情景预测叶片应在保持正碳平衡的情况下脱落。对三种热带先锋树种（番木瓜、钝叶蚁栖树和哈氏豆）幼树的碳获取和叶片动态进行的田间研究结果支持了该模型的预测，这三种树的每个茎上的叶片数量不同。结果表明，在这些快速生长的植物中，叶片产生和高度生长可能比茎的净碳输出更适合作为性能指标，并表明叶片衰老主要是叶片在树冠内位置的函数，而不是其实际年龄的函数。
