Diversity, functionality and evolution of medullosan seed ferns: Vegetation-climate interactions in a seasonally dry in-situ habitat of early Permian age

该项目重点研究早二叠世种子植物的生态和进化动态及其与晚古生代气候变化的关系。这一时期的特点是广泛的冰川作用，可与现在的冰河时代相媲美，而早二叠世的冰屋-温室过渡尤其令人感兴趣。与石炭纪的主要冰期相比，这一时期显示出关于大气二氧化碳分压的相当大的数据差距。在古气候研究中，化石植物发挥着关键作用，因为它们提供了关于降水、温度和大气中二氧化碳含量的可测量参数。然而，到目前为止，这些只从孤立的植物器官中获得，这限制了它们的古生态意义。在分布广泛的二叠纪种子植物中，髓草尤其具有高于平均水平的导水潜力，相当于现代阔叶树的导水潜力。因此，它们可以被认为是气候敏感的，因此在古气候研究中很有希望。该项目的目的是：1)调查和重建二叠纪类型开姆尼茨地区的水龙的功能，2)全植物水力模拟，以帮助优化植物古气候替代方法，3)评估一种计算早二叠世大气二氧化碳分压的新方法。化石来自开姆尼茨化石森林，这是一个原位保存的，类似绿洲的早二叠世栖息地(291myr)，在那里可以研究生物与环境之间的关系。该遗址提供了世界范围内显著的髓藻多样性，主导着这个暴露在季节性干旱中的密集的喜湿植物群落。由于火山沉积物的快速掩埋，一些树木被发现仍然直立着，以便通过考虑各种特定地点的参数，如古气候、土壤和植被，在它们的生长地点对它们进行研究。将对三种几乎保存完整的延髓动物进行调查，包括从树根到树冠的各种器官。到目前为止还没有反映出的特殊解剖细节的功能表明，这与现代苏铁类的比较，现代苏铁类是脊椎动物最接近的近亲。这包括一个中空-圆柱形水平管胞网络形式的生态相关的水储存和供应系统，以及使人想到与珊瑚状、共生活动的苏铁根进行比较的根结构。关于植物导水潜力的所有可测量参数都应在已建立的关于其古生态意义的计算方法的背景下进行确定和评估。这些关于水分传导性的解剖学数据将被用来测试一种有前景的大气二氧化碳分压模拟方法，以替代通常应用的基于叶片气孔密度的方法。

The project focuses on the ecological and evolutionary dynamics of early Permian seed plants and their relationships to climate change in the late Palaeozoic. This period was characterised by extensive glaciation, comparable to the present Ice Age, whereas the Icehouse-Greenhouse transition in the early Permian is of particular interest. In contrast to the main glaciation phase in the Carboniferous, this period shows a considerable data gap regarding the CO2 partial pressure of the atmosphere. In palaeoclimate research, fossil plants play a key role, as they provide measurable parameters on precipitation, temperature, and CO2 content of the atmosphere. However, so far, these have only been obtained from isolated plant organs, what limits their palaeoecological significance. Among the widespread Permian seed plants, medullosans in particular offer an above-average water conduction potential quite comparable to that of modern broadleaved trees. Accordingly, they can be recognised as climate-sensitive and thus promising for palaeoclimate studies.Aims of the project are: 1) Investigating and reconstructing functionality of medullosans at their Permian type locality of Chemnitz, 2) whole-plant hydraulic modeling in order to contribute to optimising methods of plant palaeoclimate proxies, 3) evaluating a novel approach for the calculation of the CO2 partial pressure of the early Permian atmosphere.The fossils originate from the Chemnitz Fossil Forest, an in-situ preserved, oasis-like habitat of early Permian age (291 myrs), in which relationships between organisms and their environment can be investigated. The site offers a worldwide remarkable diversity of medullosans, dominating this dense hygrophilous plant community that was exposed to seasonal droughts. Due to rapid burial by volcanic deposits, some of the trees were found still standing upright enabling to study them at their places of growth by taking into account a variety of site-specific parameters such as palaeoclimate, soil, and vegetation.Three almost completely preserved medullosans will be investigated including various organs from the roots to the crown. The function of special, hitherto not reflected anatomical details suggests the comparison with modern cycads, the nearest living relatives of the medullosans. This includes an ecologically relevant water storage and supply system in the form of a hollow-cylindrical, horizontal tracheid network, as well as root structures that suggest a comparison with coralloid, symbiotically active cycad roots. All measurable parameters on the water conductivity potential of plants are to be determined and evaluated in the context of established calculation methods with regard to their palaeoecological significance. These anatomical data on water conductivity will be used to test a promising approach of modeling the CO2 partial pressure of the atmosphere, alternatively to the commonly applied method based on stomata density of leaves.