Investigating wetland plant mycobiomes to develop appropriate analogues for paleomycological inquiry

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Although interactions between plants and fungi are ubiquitous in modern ecosystems and are thought to have been integral to the establishment of early terrestrial floras, the fossil record of plant-fungal interactions is sparse. Moreover, every fossil plant assemblage that contains root-associated fungi represents a wetland environment. As such, our understanding of the fossil record of plant-microbe interactions is biased towards plants living in, or near, inundated soils. The ecology of these interactions has, however, been consistently interpreted in accordance with models of plant-microbe interaction developed in subaerially exposed soil systems. Wetland soils are biogeochemically hostile environments primarily controlled by frequent anoxia with reduction-oxidation dynamics unparalleled in subaerial (fully terrestrial) soils; plant-fungal interactions in these settings have yet to be comprehensively addressed. The long-term goal of this research program is to utilize insights gained through study of contemporary plant-fungal interactions in wetland ecosystems, in order to better contextualize plant-fungal interactions in fossil wetland assemblages. The proposed research is focused on developing baseline data for root mycobiome community diversity and ecological drivers in contemporary wetlands. Studying biogeochemically-appropriate modern analogues for fossil assemblages will improve interpretation of plant-fungal interaction in the fossil record, and simultaneously establish a framework for future ecological investigations of contemporary wetlands. Short term objectives of this proposal are: 1) Evaluating host-specificity of rhizosphere mycobiome constituents across hydrologic, biogeochemical, and climatic gradients, using a combination of targeted amplicon (NL1/NL4, ITS) metagenomic sequencing and culturing (PhD 1). 2) Investigating congruence of wetland plant mycobiomes with rhizosphere spore banks, using metagenomic and visual assays (PhD 2). 3) Developing a culture library and database of host-fungal associations (conducted by MSc students, undergraduate researchers), as a line of evidence independent of sequencing, and for future investigation of plant physiologic response to individual constituents of root mycobiomes, fungal species discovery, and evaluating diversity of endohyphal bacteria. These investigations build foundational knowledge in as-yet understudied biological systems. From a paleobiology perspective, these studies will facilitate productive approaches to studying the fossil record of plant-fungal interactions, and more accurate interpretations of fossil floras during key intervals of plant evolution and global climatic change. In its initial 5 years, this research program will train 3 summer undergraduate researchers per year in field ecology and laboratory mycology methods, and 5 graduate researchers in metagenomic, culturing, and ecology data collection and analysis.