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What's the Holdup? Temperature Limitations to Enzyme-Catalyzed Arctic Soil Decomposition

Whittington, Ruth
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1557487398712549

Abstract Details

2019, Master of Science, University of Toledo, Biology (Ecology).
Arctic ecosystems contain globally important terrestrial carbon stocks, and their temperatures are rising at twice global rates. While increasing temperatures lead to faster decomposition and carbon mineralization rates, predicting the magnitude and future patterns of soil respiration is difficult due to multiple interacting direct and indirect effects. In particular, we lack mechanistic data on how low temperatures impact extracellular enzyme activities and thereby determine carbon supply rates to respiration. For this research, I performed two laboratory soil incubations designed to measure the temperature responses of enzymes catalyzing the terminal steps in Arctic tundra soil organic matter depolymerization. These experiments were designed to first characterize microbial activity responses to temperature based on cumulative carbon loss, and then to identify how substrate and nutrient availability mediate indirect temperature responses. In the first experiment, tundra soils were incubated across a temperature gradient from 4 - 20 °C and subsequently harvested at four time points at comparable levels of cumulative carbon loss. Comparing temperature effects on respiration rates as they changed with greater substrate depletion, respiration temperature sensitivity declined over time, likely due to declining substrate availability at higher temperatures. In contrast, enzyme temperature sensitivity increased over time, an apparent consequence of increased enzyme production at higher temperatures. These results indicate that carbon flow from depolymerization may not be high enough to sustain microbial activity below 10 °C and may explain observations of unexpectedly high increases in soil respiration with temperature in this range. In a second experiment, labile carbon was added with and without nutrients to tundra soils incubated at 8 and 16 °C and subsequently harvested at three points based on cumulative carbon loss from control soils. Respiration temperature sensitivity increased following labile carbon addition, indicating low substrate availability suppressed temperature responses from control soils. Temperature limitations to enzyme production persisted across all treatments, suggesting limitations to enzyme production may be due to lower microbial demand at low temperatures. Overall, results from this research demonstrate a number of indirect temperature effects on enzyme production and carbon availability that are currently unaccounted for in predictive Earth system models. Furthermore, they suggest that both enzyme production and activity are likely to increase as Arctic soils warm, two mechanisms by which temperature rise may increase carbon transfer from tundra soils to the atmosphere.
Michael N. Weintraub (Committee Chair)
Daryl L. Moorhead (Committee Member)
Patrick F. Sullivan (Committee Member)
144 p.
Biogeochemistry; Biology; Ecology; Environmental Science
soil decomposition, extracellular enzymes, temperature limitations, carbon cycling, Arctic soil decomposition, carbon availability, nutrient availability,

Recommended Citations

Citations

  • Whittington, R. (2019). What's the Holdup? Temperature Limitations to Enzyme-Catalyzed Arctic Soil Decomposition [Master's thesis, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1557487398712549

    APA Style (7th edition)

  • Whittington, Ruth. What's the Holdup? Temperature Limitations to Enzyme-Catalyzed Arctic Soil Decomposition. 2019. University of Toledo, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1557487398712549.

    MLA Style (8th edition)

  • Whittington, Ruth. "What's the Holdup? Temperature Limitations to Enzyme-Catalyzed Arctic Soil Decomposition." Master's thesis, University of Toledo, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1557487398712549

    Chicago Manual of Style (17th edition)

toledo1557487398712549
223
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This open access ETD is published by University of Toledo and OhioLINK.