The orchid root with the velamen radicum: a multifunctional organ

真正的附生与相当不稳定的水和营养供应有关。兰花根的根膜，即成熟时带有死细胞的多重表皮，其内部与外表皮接壤，外表皮的特征是1)厚壁细胞和2)所谓的传代细胞，是对附生生活方式的“适应”的教科书范例。文献中有许多关于其功能的典故，但仔细观察，可靠的实验证据极其有限。我们将测试建议的最重要的功能。为此，我们的工作有生理成分，例如，我们将研究重要营养元素的摄取动力学，水的摄取和损失，量化筋膜的离子交换能力，并研究筋膜在防止活皮层过热中的所谓作用。这些生理数据将通过在群落水平上研究根的原位人口统计学以及根的解剖和形态在环境梯度上的变化而置于生态背景中。系统地比较解剖学/形态学与生理学也将使我们能够在系统发育框架中将形式与功能联系起来。总之，我们的工作将最终创建一个明确的评价附生兰花膜的功能的数据。然而，也有许多陆生植物具有片瓣（例如兰科或天冬科），并且有许多其他附生植物具有片瓣，特别是在天南星科。因此，目前的研究只是第一步。在第二阶段，拟议的项目打算超越“附生植物”和“兰花”的主题，通过解决velententroots的主要生态和进化“维度”。

True epiphytism is associated with a rather precarious supply of water and nutrients. The velamen radicum of orchid roots, i.e. a multiple epidermis with dead cells at maturity, which borders internally on an exodermis that features 1) thick-walled cells and 2) so-called passage cells, is a textbook example of an ´adaptation´ to the epiphytic life style. There are numerous allusions to its function in the literature, but at close inspection solid experimental evidence is extremely limited. We will test the most important of the suggested functions. To this end, our work has physiological components, e.g. we will study uptake kinetics of important nutrient elements, water uptake and loss, quantify the ion exchange capacity of the velamen, and investigate the alleged role of the velamen in preventing overheating of the living cortex. These physiological data will be put in an ecological context by studying in situ root demography and variation in root anatomy and morphology at the community level along environmental gradients. Systematically comparing anatomy / morphology with physiology will also allow us to link form with function in a phylogenetic framework. In summary, our work will finally create the data for an unambiguous evaluation of the function of the velamen in epiphytic orchids. However, there are also numerous terrestrial plants with a velamen (e.g. in Orchidaceae or Asparagaceae), and there are numerous other epiphytes with a velamen, particularly in the Araceae. Thus, the current study is just a first step. In a second phase the proposed project intends to go beyond the topics ´epiphytes´ and ´orchids´ by addressing the major ecological and evolutionary ´dimensions´ of velamentous roots in general.