Date of Award

Summer 2019

Project Type


Program or Major

Natural Resources

Degree Name

Master of Science

First Advisor

Serita D Frey

Second Advisor

Stuart A Grandy

Third Advisor

Kevin M Geyer


Microbial carbon use efficiency (CUE; the proportion of assimilated C allocated towards biomass production) is a powerful regulator of global soil C stocks, and there is a need to integrate accurate and dynamic CUE parameters into C-cycling models. However, there is uncertainty in the CUE-response to warming and increased N deposition and how this response may vary among groups of microbes. Here, we conducted a laboratory incubation of ten photogenically diverse fungal isolates grown in liquid culture to evaluate potential environmental and physiological controls over CUE. Isolates were grown at 15ºC or 25ºC and under low or high N concentrations. We measured respiration rates, growth rates, CUE, and a suite of potential extracellular enzyme activities. We show that CUE was consistently reduced at elevated temperatures due to increased respiration and decreased growth rates. Additionally, we show that overall N addition did not significantly impact respiration, growth, or CUE. However, there were N addition effects that were group- and species-specific. Further, we show that there are tradeoffs between physiological traits, such as growth rate and resource acquisition, that result in distinct growth strategies among phylogenetic groups. Our work demonstrates that there are significant environmental and physiological controls over microbial CUE and that CUE is similar and predictable among distinct phylogenetic groups of fungi.