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The Q10 coefficient is the ratio of reaction rates at two temperatures 10°C apart, and has been widely applied to quantify the temperature sensitivity of organic matter decomposition. However, biogeochemists and ecologists have long recognized that a constant Q10 coefficient does not describe the temperature sensitivity of organic matter decomposition accurately. To examine the consequences of the constant Q10 assumption, we built a biogeochemical reaction model to simulate anaerobic organic matter decomposition in peatlands in the Upper Peninsula of Michigan, USA, and compared the simulation results to the predictions with Q10 coefficients. By accounting for the reactions of extracellular enzymes, mesophilic fermenting and methanogenic microbes, and their temperature responses, the biogeochemical reaction model reproduces the observations of previous laboratory incubation experiments, including the temporal variations in the concentrations of dissolved organic carbon, acetate, dihydrogen, carbon dioxide, and methane, and confirms that fermentation limits the progress of anaerobic organic matter decomposition. The modeling results illustrate the oversimplification inherent in the constant Q10 assumption and how the assumption undermines the kinetic prediction of anaerobic organic matter decomposition. In particular, the model predicts that between 5°C and 30°C, the decomposition rate increases almost linearly with increasing temperature, which stands in sharp contrast to the exponential relationship given by the Q10 coefficient. As a result, the constant Q10 approach tends to underestimate the rates of organic matter decomposition within the temperature ranges where Q10 values are determined, and overestimate the rates outside the temperature ranges. The results also show how biogeochemical reaction modeling, combined with laboratory experiments, can help uncover the temperature sensitivity of organic matter decomposition arising from underlying catalytic mechanisms.
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Low temperature sensitivity of picophytoplankton P:B ratios and growth rates across a natural 10°C temperature gradient in the oligotrophic Indian Ocean
We investigated temperature sensitivities of picophytoplankton growth along a natural 10°C (18-28°C) temperature gradient in the eastern Indian Ocean characterized by deep mixing and consistently low dissolved nitrogen. Population biomass (B), cell carbon and chlorophyll were measured by flow cytometry. Instantaneous growth (µ) and production (P) were calculated from dilution incubations at four light levels. Contrary to most empirical and theoretical predictions, Prochlorococcus, the biomass dominant, showed insignificant temperature sensitivity, with nominal Q10 values of 1.06 and 1.18 for P:B and µ, respectively, and activation energies (Ea) of 0.05 and 0.12 eV. Q10 and Ea values for Synechococcus (1.36-1.42 and 0.23-0.27 eV) were also below prediction, and picoeukaryotes showed high variability, including negative rates suggesting lytic cycles, at high temperature. We emphasize the importance of using adapted communities in natural environmental gradients to test climate predictions and hypothesize that mortality defenses are a significant selection criterion in balanced oligotrophic systems.
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- Award ID(s):
- 1851558
- PAR ID:
- 10334678
- Date Published:
- Journal Name:
- Limnology and oceanography letters
- Volume:
- 7
- ISSN:
- 2378-2242
- Page Range / eLocation ID:
- 112–121
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/doi.org/10.1002/lol2.10224.
