Plant–microbe interactions in deep time: A multidisciplinary study of Permian microorganisms associated with tree ferns, and their responses to climate change

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The end of the late Paleozoic ice age (Pennsylvanian-Permian) resulted in considerable changes of vegetation dynamics and repeated variations in tropical climate. This time interval can therefore be viewed as an analogue of present-day global change. While many studies have focused on the parameters causing profound changes and large-scale effects on the ecosystems that occurred during this dynamic period of time, small-scale investigations that address specific organismal interactions in local communities are very rare. The lower Permian of Manebach, Germany, part of the Thuringian Forest Basin reference section, have been collected for nearly 200 years, in particular for specimens of the globally distributed tree fern Psaronius. As several recent studies have provided new insights into geology, stratigraphy, palaeoecology and -climatology of that site, a more complete characterization of the palaeoecosystem and one of its major plant constituents has now become possible and will provide insights into the geo-biological constraints of its life and preservation. Based on exceptionally well preserved historical specimens and newly collected ones, we will investigate the diverse assemblages of fungi and fungus-like microorganisms that occur within the different tissues of Psaronius and other 3D-preserved plants. We will document the diversity of microbes associated with the plants, map out their distribution patterns, and assess the biological nature of the various microbial interactions with the host plants in order to understand the levels of interrelatedness that characterized individual plants as habitats and micro-ecosystems. We will investigate the taphonomic conditions and pathways that have led to the exceptional preservation of microorganisms within the plants. Following the 2016 excavation, we have initiated research on the sedimentary environment and specific preservation circumstances that have resulted in unique snapshots of the ecosystem. We submit that the outcomes from our research will substantially increase the knowledge of the interrelationships between plants and microbes and how they responded to climate and environmental change in the early Permian. We will contribute to a better understanding of the roles different microorganisms played in the ecosystems in which they lived, and how they affected the evolution of terrestrial communities. Study will focus on a dynamic palaeoenvironment that was nested within an interregional traceable wet phase in the Cisuralian and represents one of the last coal swamp refugia in the Variscan interior. Our integrative approach encompasses methods, e.g., geological field work, light-microscopic anatomical study based on thin sections, cathodoluminescence and scanning electron microscopy with orientation contrast imaging by backscattered electrons and electron backscatter diffraction, and gas chromatography–mass spectrometry geochemical studies to assess taphonomic processes and constraints.