Disentangling the Role of Microorganisms in Ecosystem Function: A Microbiological Perspective on Environmental Issues

Emily Bonnell Graham, University of Colorado Boulder

Abstract

Microorganisms are vital in regulating the earth’s diverse habitats by mediating a wide range of biogeochemical processes. Recent advances in genomic sequencing have allowed for greater resolution of microbial complexity in the environment; yet, links between microbial communities and ecosystem-level processes remain poorly understood. Microbial community structure – ecosystem function relationships vary across space and time with a variety of ecological dynamics, and knowledge on these connections is essential to predicting ecosystem responses to future environmental change.

As such, my work spans a gradient of scales, from exploring global patterns in relationships between microbial community structure and ecosystem function to focusing on fine-scale interactions between dissolved organic matter, microbial communities, and mercury methylation within the largest port in the U.S. Great Lakes. First, I examine broad trends in microbial communities and biogeochemical processes through investigating a central question in microbial ecology, ‘Under what circumstances does information on microbial community composition add to our explanatory power of ecosystem processes?’ I address this question using statistical methodology to examine the importance of microbial data for explaining nitrogen cycling within a tropical forest across two distinct seasons, and then I standardize and extend this approach to 82 diverse datasets I collected by leading a global collaboration effort. My results indicate that, in general, the value of microbial data for explaining rates of ecosystem processes is maximized when functional attributes of the community are measured; however, this result varies with the phylogenetic breadth of the process and with ecosystem type. At a smaller scale, I use a suite of techniques from limnology, biogeochemistry, and microbial ecology to show that links between sediment microbial communities, dissolved organic matter fluorescence characteristics, and mercury methylation vary across chemically discrete sediments in a mining contaminated freshwater estuary. Moreover, I identify a previously under-considered clade of microorganisms as potential key methylators within oligotrophic environments in this system.

As a whole, my work addresses fundamental questions within microbial ecology and ecosystem science at an array of scales and enhances knowledge on patterns in microbial community structure – ecosystem function relationships that are imperative for comprehending future ecosystem functioning under environmental change.