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

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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.