Application of canopy photosythesis models to the analysis of leaf phenology

叶片的寿命比个体的寿命短，植物在生长期产生和脱落叶片。不同树种的叶片产生和脱落模式不同，常绿树种和落叶树种就是如此。我们认为叶片物候期的差异是植物适应环境变化的一种策略。将冠层光合作用模型应用于叶片物候分析，建立了新的叶片动态和氮素模型。该模型预测了最佳叶面积指数、冠层光合作用、叶片寿命、氮素利用效率，以及它们对氮素和光有效性变化的反应。在人工建立的草本林中，我们分析了影响产叶和落叶的因素。遮荫叶片叶面积损失率随着氮素再运转量的增加而增加，以满足植株生长对氮素的需求。我们的研究表明，在氮素利用率较低的情况下，保持较长时间的叶片有助于植物的生长，而在氮素利用率较高的情况下，叶片不会被丢弃，尽管与叶片损失相关的氮素的重新转移会增加植物的总生长速率。在山毛榉森林中，我们发现树冠和林下树种对N的吸收速率相似，并不依赖于光的可获得性。在同一林分中，冠层和林下树种间叶片水平氮素利用效率差异不显著，但其作用机制存在较大差异。冠层植物具有较高的N生产力，平均停留时间较低，而林下植物具有较高的N停留时间，较低的N生产力。我们研究了叶片光合作用对环境变化的响应。利用叶肉细胞表面的空隙来容纳扩大的叶绿体，对于积极应对突然增加的光照气候是必不可少的。

The lifespan of leaves is shorter than that of individuals, and plants produce and shed their leaves in the growth period. The pattern of leaf production and shedding is different among species as is represented in evergreen and deciduous species. We considered difference in leaf phenology as a strategy of plants to adapt themselves to changing environments. Applying a canopy photosynthesis model to the analysis of leaf phenology, we developed a new model of leaf dynamics and nitrogen. The model predicted optimal LAI, canopy photosynthesis, leaf lifespan, nitrogen use efficiency, and also their responses to changes in nitrogen and light availability. In experimentally established herbaceous stands, we analysed the factors responsible for leaf production and shedding. Leaf area loss rate increased in shaded leaves with an increase in N retranslocation to meet the N demand for growth of the plant. We demonstrated that leaves were discarded Oven though maintaining those leaves longer would contribute to plant growth at low N availability, while at high N availability leaves were not discarded even though retranslocation of N associated with leaf loss would increase total plant growth rate. In a beech forest, we found that canopy and understorey tree species had a similar N resorption rate that did not depend on the light availability. In the same forest, we found that leaf level N use efficiency was not significantly different between canopy and understorey species, though the mechanism was very different from each other. Canopy species had a high N productivity with a low mean residence time of N, while understorey species had a high residence time of N with a low N productivity. We studied responses of leaf photosynthesis to environmental changes. Availability of vacant space in mesophyll cell surfaces to accomodate enlarged chloroplasts is indispensable to positively respond to sudden increase in light climate.