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Project Progress

During the 2006-2007 year significant progress has been made characterizing the ecological and evolutionary history of fungal symbionts in early land plants. 80-90% of all land plants have mutualistic symbiotic associations with fungi where the fungal symbionts provide increased access to essential minerals and the fungal symbionts gain fixed carbon. We are characterizing the fungal symbionts in early lineages of land plants (over 300 million years old) that have a life cycle where one phase is above ground and photosynthetic and another phase is completely underground for as long as fifteen years. This subterranean phase in these poorly understood plants is completely dependant on a set of fungal symbionts to provide a source of fixed carbon. These early lineages represent a potential ancient life cycle mode that succeeded based on its fungal dependant subterranean phase. Given the number of known asteroid impacts from K-T to Late Devonian, early land plant lineages with long-lived subterranean phases were potentially less affected by drastic changes in the above ground environment and therefore have persisted for hundreds of millions of years. To date, the fungal symbionts throughout the life cycle in early land plant lineages (Lycopodiaceae, Psilotales and Ophioglossales) have been identified using sequence data. In addition to studying the fungal symbionts within early land plants, we have identified the fungal symbionts in photosynthetic neighboring plants to place our data in a larger ecological and evolutionary framework. Based on our sequence data, subterranean phases of the life cycle in these early land plant lineages obtain fixed carbon through an extensive fungal network with conspecific and heterospecific neighboring plants. Additionally, our analyses have identified two entirely new clades of fungi that form associations with subterranean plants. Furthermore, based on the diversity of fungi that we have identified, it is apparent that multiple species of fungi and multiple species of plants have independently evolved the ability to form plant-fungal associations where the fungus provides the plant with fixed carbon. Thus, given the diversity of fungal species capable of translocating carbon between photosynthetic plants and subterranean plants, it is possible, if not probable, that carbon transfer between different plant species through fungal networks may well extend beyond underground plants.