"Examining the role of microbial communities in soil carbon cycling acr" by Chansotheary Dang

Author ORCID Identifier

https://orcid.org/0009-0009-1232-0945

Semester

Fall

Date of Graduation

2024

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Applied and Environmental Biology

Committee Chair

Ember M. Morrissey

Committee Member

Edward R. Brozostek

Committee Member

Louis M. McDonald

Committee Member

William T. Peterjohn

Committee Member

Zachary B. Freedman

Abstract

Microorganisms provide the foundation for many ecosystem processes and are important drivers of carbon and nutrient cycling. The advancement of next generation sequencing has allowed researchers to lift open the lid on the ‘black box’ in microbial ecology. While previously unculturable microbes can now be characterized with the 16S rRNA gene, answering ‘who’s there?’ is only part of the challenge. Hidden inside the ‘black box’ remains the question, ‘who’s doing what?’. Recent development in trait-based methods like quantitative stable isotope probing (qSIP) equipped microbial ecologists with the tool to connect taxon-specific traits to ecosystem processes. Despite the growing body of information, linking microbial communities’ dynamics to ecosystem functions remain challenging. This raises the critical question: how can we move forward from descriptive studies towards a more mechanistic understanding of microbial ecology? Potentially, identifying ecologically relevant traits that reflect microbial life history strategies may offer insights into how microbes interact with their environment and respond to changes. My PhD dissertation investigates how microbial body size and growth rate can be used to explore community dynamics, identify ecological interactions, classify trophic strategies, and understand carbon biogeochemistry. I found that body size is a fundamental trait that shapes the overall community functional potential and interactions, all of which have a cascading effect on the carbon use efficiency. Next, I examined how growth rates can be used to provide biological insights into refining the oligotroph-copiotroph framework. I demonstrated that growth rates are evolutionarily constrained and consistent across different soil environments, providing a useful metric for classifying microorganisms into trophic strategy. While this framework is far from perfect, adding a ‘mesotrophic’ group to represent microbes with intermediate growth rates better captures the continuous nature of microbial traits. Lastly, I explored how examining the actively growing bacteria population and scaling community function can be used to unveil the mechanisms driving carbon cycling responses to global change. Here, I showed that the active bacteria community found in arbuscular and ectomycorrhizal soil responded differently to elevated N. These differences were driven by the interactions between plants, mycorrhizae, and bacteria community, which was reflected in the carbon mineralization rates between the two ecosystems. Altogether, linking microbial traits like body size and growth rates to community dynamics and ecosystem processes can deepen our understanding of the microbial mechanisms driving carbon cycling. As we continue exploring the role of microbial traits in linking microbial processes to ecosystem function, we can develop and refine microbial ecological theory to better capture microbial diversity and improve ecosystem models.

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