Understanding how microbial communities assemble and together generate aggregate ecosystem functions is a critical but understudied aspect of earth?s systems. Wood decomposition in water is one such important ecosystem function. This process is a critical component of the global carbon cycle, but the diversity of aquatic organisms that decompose woody mass, the assembly of those taxa into diverse communities depending on the surrounding environment, and the various environmental controls on the rate and trajectory of wood decay are not well understood - particularly in the tropics. In this project, we use a large-scale and long-running (15 month) wood decomposition experiment replicated across three undisturbed freshwater-estuarine river systems in Pacific coastal Panama and the resulting collection of aquatic fungi cultures to: (1) Describe the diversity of aquatic fungi along a salinity gradient using both classical culture-based approaches and high-throughput DNA sequencing, (2) Connect microbial community shifts to the process and rate of wood decomposition by measuring wood biomass loss, fungal enzyme production, wood structural polymers, and wood nutrient composition, (3) Study the genomic basis of fungal wood decay by measuring gene expression responses of wood decay fungi to wood substrates across salinity environments in the lab. 

Our results comparing culture-based and DNA sequence-based sampling uphold the classical turnover between freshwater and marine aquatic fungi, and our decomposition experiment demonstrates strong and consistent differences in decay rates and trajectories among salinity environments coordinate with shifts in the microbial communities. Our gene expression results show that fungal genomes are regulated in a highly dynamic fashion in response to salinity and wood substrate, suggesting that the process of wood decomposition depends on the interaction between fungal taxa, environmental response, and wood substrate availability. In addition, we are in the process of describing several new species of aquatic fungi. We have also answered several additional questions including: 1) How do decay organisms and decay processes differ in water versus on land? 2) How do the microbial communities and process of decay differ between bark and underlying wood? 3) How does the nutrient environment that surrounds decaying wood, versus the nutrient content of the wood itself, affect rates of wood decay? 4) How do different pH and salinity conditions determine the production of critical decomposing enzymes in both freshwater and marine fungi?Our findings have important implications for global ecosystem-level processes by revealing sources of variation in carbon cycling (e.g., bark, salinity environment) and also implicating aquatic wood decay in explaining missing components of the carbon cycle. Our results are also important for fungal ecology and evolution by better defining aquatic decomposer communities, how they function, and how they assemble depending on salinity environment. Together our results contribute to a growing understanding for how microbial taxa come together, regulate the expression of functional genes in their diverse genomes, and respond to various environmental conditions to generate critical ecosystem services that sustain natural ecosystems.

As part of our project, we have trained numerous scientists from the United States and Panama. In Illinois, this includes one postdoc who has since moved on to a faculty position, one PhD student who is starting a research postdoc position, plus one collaborating MS student from Eastern Illinois University who has entered a PhD program with a Fulbright. In addition, we have trained several undergraduate researchers at University of Illinois in laboratory techniques. At our field sites in Panama, we collaborated with regional universities to train students in field ecology and mycology, teach a workshop in ecology, and give Spanish-language presentations to students, the public and partner institutions. Through these activities in collaboration with the Smithsonian Tropical Research Institute in Panama, we have trained five interns. Two of our Panamanian interns were admitted to graduate school. One receiveda Fulbright and just completed his MS thesis at Univ. Arkansas studying bacteria in extreme environments, and the second just started her PhD at Univ. Georgia studying tropical disease. In addition to project trainees, our collaboration supported one beginning female minority investigator and one early career female investigator. Our project has generated numerous resources for the larger scientific community, including novel, undescribed species and clarifying species identifications of these important but understudied fungal groups, numerous gene sequences for hundreds of aquatic fungi for public databases and the scientific community more generally, and novel transcriptomes (expressed gene databases) for non-model aquatic fungi with important wood decay functions that will be of interest to scientists in basic research and industry alike.

Last Modified: 11/29/2018
Modified by: Katy D Heath