Effects of carbon and nitrogen interactions on terrestrial ecosystems

我们建立了植物生长模型和生态系统模型，特别参考了碳氮相互作用。然后我们试着检验这些模型的预测结果。植物的最佳物质分配取决于灵魂肥力、植物形状和生活史。该模型预测的叶片含氮量（即光合能力）与田间实测结果相似。固氮桤木在秋季不吸收衰老叶片中的氮。因此，桤木在秋季生长期延长。在延长的生长期，桤木吸收的能量约为补偿氮损失所需能量的6倍。相对于固氮落叶乔木不吸收氮的特性，这种能量盈余平衡具有优势。我们的氮竞争模型预测寒温带的天然植被必须是落叶乔木和常绿针叶林混交林。然而，不含针叶林的落叶森林在该地区广泛分布。对阔叶林下针叶树的伸长生长进行了测量。结果表明，针叶树幼树从萌芽到生长到落叶林冠层需要100年的时间。这支持了模型的预测。寒温带的落叶森林很可能是由于持续的砍伐而形成的次生林。大约40年前，日本人把他们的能源从树木改为石油。因此，次生落叶林正在向天然混交林回归。

We developed a growth model of plants and a ecosystem model with special reference to carbon and nitrogen interactions. Then we tried to test the predictions of the models.1. Optimal matter partitioning of plants depends on soul fertility, plant shape, and life history. Leaf nitrogen contents (i.e. photosynthetic capacity) predicted by the model are similar to those measured in the fields.2. Nitrogen-fixing alder does not resorb nitrogen form senescing leaves in autumn. As a result, the alder has growth period extension in autumn. The amount of energy assimilated by the alder in the extended growth period was about six times that required for compensating the nitrogen loss. This surplus energy balance provides an advantage over the non-nitrogen-resorbing trait of nitrogen-fixing deciduous trees.3. Our nitrogen competition model predicted that natural vegetation in the cool temperate zone must be mixed forest of deciduous trees and evergreen conifers. However, deciduous forests without the conifers are widely distributed in the zone. We measured the elongation growth of understory conifers in the deciduous forests. We showed that the saplings of conifers attain the forest canopy of the deciduous forests within 100 years from their germination. This support the model prediction. Probably, the deciduous forests in the cool temperate zone are secondary forests caused by continual fellings. About 40 year ago, Japanese people changed their energy source from trees to petroleum. Accordingly, the secondary deciduous forests are returning to natural mixed forest.