Costs and benefits in branching and the mechanical stability of plants

植物构型是与植物的光截获和机械稳定性有关的总体形态学。我们的目的是测试植物在特定环境中发展叶子以有效拦截光线的假设。植物单独生长或密集的林分有不同的光气候。在头两年，我们进行了一个实验，使用一年生藜专辑。描述了孤生林和密生林植物的结构，分析了它们的生长情况。根据叶面积分布，计算了植物的光截获量。为了描述植物结构，我们使用植物体，植物体是由节间、叶柄和叶片组成的植物生长单位。分析了孤生林和密生林植物在分枝格局和资源利用上的差异。密生林比单生林更瘦、更高。孤生植物产生更多和更长的分支。密集的植物以机械稳定性为代价长高。光利用效率较高，氮利用效率较低，在密集的立场比孤立的plants.From第二年，我们使用另一年生植物加拿大苍耳，以确定参与的延伸生长和机械稳定性的植物的因素。我们测量了节间的弹性模量和断裂应力，发现两者都低于在孤立比密集的立场植物，但对屈曲的安全系数较大的孤立植物，由于其较低的雕像。弹性模量、断裂应力与节间干质量密度呈正相关关系，但密度与单株间的回归关系差异显著;分析了节间相对伸长速率与含水量的关系。水分含量与节间干物质密度呈极强的相关性。这种关系是用一个简单的模型推导出来的，该模型包括干物质密度和空气空间分数作为参数。

Plant architecture is gross morphology pertaining to light interception and mechanical stability of plants. We aimed to test the hypothesis that plants develop their leaves to efficiently intercept light in a given environment. Plants were grown solitarily or in dense stands to have different light climates.In the first two years, we conducted an experiment using an annual Chenopodium album. We described the architecture of solitary and dense-stand plants and analyzed their growth. From leaf area distribution, we calculated light interception of the plants. To describe plant architecture, we used phytomers, a unit of plant growth each composed of an internode, petiole and leaf blade. Differences in branching pattern and resource use between solitary and dense-stand plants were analyzed. Dense-stand plants were thinner and taller than solitary plants. Solitary plants produced more and longer branches. Dense-plants grew taller at the expense of mechanical stability. Light use efficiency was higher and nitrogen use efficiency was lower in dense-stand plants than solitary plants.From the second year, we used another annual species Xanthium canadense to identify factors involved in extension growth and in mechanical stability of plants. We measured the elastic modulus and breaking stress of internodes and found that both were lower in solitary than dense-stand plants but that the safety factor against buckling was larger in solitary plants due to their lower statue. There were positive correlations between elastic modulus, breaking stress and dry mass density of internodes, but the regressions were significantly different between solitary and dense-stand plants.Relationships between the relative elongation rate and water content of internodes were analyzed. There was a strong correlation between water content and dry mass density of internodes. This relationship was derived with a simple model that includes density of dry mass and fraction of air space as parameters.