Advanced Techniques for the Study of Plant Interactions with Fungi and Other Microorganisms in Early Environments

Microorganisms are key to our understanding of early life on land, especially in terms of below-ground processes. In the fossil record, exceptionally preserved silicified systems are the best sources to document the diversity of Fungi and microorganisms and the roles that they played, including their interactions with plants. Continued advances in technology allow us to document these in unprecedent detail at sites like the Rhynie cherts (Scotland, UK), dating to 407 Ma, and the Grand Croix chert (Massif Central, France), dating to ca 307 ̶ 303 Ma. Techniques we used include Confocal Laser Scanning Microscopy (CLSM) and Laser-Induced Breakdown Spectroscopy (LIBS)-based imaging, among others.In the Rhynie cherts, plant-fungal associations and glomeromycotan spores have been observed as well as other diverse microorganisms colonizing the substrate. In modern vascular plants, endomycorrhizas are typically associated with roots, but most of the vascular plants at Rhynie were rootless, and endomycorrhizas developed in aerial axes. This is probably the plesiomorphic state for land plants. Data from Grand Croix demonstrate that by the end of the Carboniferous, endomycorrhizas had become associated with the root systems of trees. The evolution of the endomycorrhizal symbioses during the Paleozoic, from early plants to trees, is associated with important changes in the nature of the symbiosis, the structure of the soil, and changes in level of carbon dioxide gas in the atmosphere. Using a combination of techniques to decipher the nature of the organisms and their interactions is as an area of developing interest, particularly in the context of recent work on modern relatives.