Application of canopy photosythesis models to the analysis of leaf phenology

叶片的寿命比个体短，植物在生长期产生和脱落叶片。不同树种的叶片生产和脱落模式不同，常绿和落叶树种的叶片生产和脱落模式不同。我们认为叶片物候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，建立了叶片动态与氮素的新模型。该模型预测了最优LAI、冠层光合作用、叶片寿命、氮利用效率及其对氮、光效变化的响应。在实验建立的草本林分上，分析了叶片生产和脱落的影响因素。遮荫叶片的叶面积损失率随着氮再转运的增加而增加，以满足植物生长对氮的需求。研究表明，在低氮有效度条件下，叶片被丢弃，尽管维持这些叶片较长时间有助于植物生长，而在高氮有效度条件下，即使与叶片损失相关的氮重转运会提高植物的总体生长速度，叶片也不会被丢弃。在山毛榉林中，我们发现树冠和林下树种具有相似的氮吸收速率，且不依赖于光的可用性。在同一森林中，不同林下物种间叶片水平氮利用效率差异不显著，但作用机制存在较大差异。冠层种氮生产力高，平均氮停留时间短，林下种氮停留时间长，平均氮生产力低。研究了叶片光合作用对环境变化的响应。叶肉细胞表面有空位以容纳扩大的叶绿体，这是对光照气候突然增加的积极响应所必不可少的。

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.