Effects of carbon and nitrogen interactions on terrestrial ecosystems

我们开发了一个植物生长模型和一个生态系统模型，特别是碳和氮的相互作用。然后我们试图测试模型的预测。1.植物的最佳物质分配取决于灵魂的生育能力，植物的形状和生命历史。模型预测的叶片氮含量（即光合能力）与田间实测结果基本一致.固氮的桤木在秋季不吸收衰老叶片中的氮。因此，桤木在秋季的生长期延长。桤木在延长的生长期内吸收的能量约为补偿氮素损失所需能量的6倍。这种过剩的能量平衡提供了一个优势，比非氮再吸收特性的固氮落叶树。我们的氮竞争模型预测，在冷温带的天然植被必须是落叶乔木和万年青针叶树的混交林。然而，没有针叶树的落叶林在该地带广泛分布。对落叶林下针叶树的伸长生长进行了测定。我们发现，针叶树的幼苗达到森林冠层的落叶林在100年内从他们的萌芽。这支持了模型的预测。寒温带的落叶林很可能是由连续砍伐形成的次生林。大约40年前，日本人将他们的能源从树木转向石油。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.