EGU2020-604, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-604
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Legacy of constant and diurnally oscillating temperatures on soil respiration and microbial community structure.

Adetunji Alex Adekanmbi, Yiran Zou, Xin Shu, Liz Shaw, and Tom Sizmur
Adetunji Alex Adekanmbi et al.
  • University of Reading, England, School of Archaeology Geography and Environmental Science, Geography and Environmental Science, Reading, , United Kingdom of Great Britain and Northern Ireland (a.a.adekanmbi@pgr.reading.ac.uk)

Increasing temperatures due to the greenhouse effect are known to increase soil respiration, releasing more CO2 into the atmosphere and resulting in a positive feedback in our climate system. Diurnal oscillations in air temperatures influence soil temperatures and thus may affect soil microbial activities and organic carbon vulnerability. Laboratory incubation studies evaluating the temperature sensitivity of soil respiration frequently use measurements of respiration taken at a constant incubation temperature in soil that has also been pre-incubated at a constant temperature.  However, such constant temperature incubations do not represent the field situation, where soils undergo diurnal oscillations in temperate under the influence of changing air temperature. We investigated the effects of constant and diurnally oscillating temperatures on soil respiration, organic matter and soil microbial community composition. A Grassland soil from the UK was either incubated at a constant temperature of 5, 10 or 15 ºC , or diurnally oscillated between 5 and 15 ºC (increasing or decreasing at 2.5 ºC for 3 hour intervals within each 24 hours). Soil CO2 flux was measured by temporarily moving incubated soils from each of the abovementioned treatments to 5, 10 or 15 ºC, such that soils incubated at each temperature had CO2 flux measured at every temperature. Our approach used incubation and measurement temperatures as factors to explore the influence of incubation temperature on the respiration at the measured temperature and to determine temperature sensitivity of CO2 flux for each incubation treatment. We hypothesised that a higher measurement temperature would result in greater CO2 flux and that, irrespective of measurement temperature, CO2 emitted from the 5 to 15 ºC oscillating incubation would be similar to that from the 10 ºC incubation. The results showed that both incubation and measurement temperatures influence soil respiration differently. Soil respiration measured at 15 ºC was greater than that of 5 and 10 ºC, irrespective of the incubation temperature. Incubating soil at a temperature oscillating between 5 and 15 oC resulted in greater CO2 flux than constant incubations at 10 ºC or 5 ºC, but was statistically similar to 15 ºC. This may be because extracellular depolymerisation is the rate limiting step in soil respiration and the time spent at 15 ºC in the oscillating treatment was sufficient to depolymerise enough polysaccharides to maximise intracellular respiration. The greater CO2 release in soils incubated at 15 ºC or oscillating between 5 and 15 ºC coincided with depletion of the soil organic carbon and a shift in the phospholipid fatty acid profile of the soil microbial community, consistent with thermal adaptation to higher temperatures. Dissolved organic carbon and C/N ratio significantly decreased in soils incubated at 15 ºC or oscillating between 5 and 15 ºC with attendant increase in the ratios of Gram negative to positive bacteria and cis/trans ratio, and decreased Fungi/Bacteria ratio. Our results suggest that daily maximum temperatures are more important than daily minimum or average temperatures when considering the response of soils to warming. 

 

How to cite: Adekanmbi, A. A., Zou, Y., Shu, X., Shaw, L., and Sizmur, T.: Legacy of constant and diurnally oscillating temperatures on soil respiration and microbial community structure., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-604, https://doi.org/10.5194/egusphere-egu2020-604, 2019

Comments on the presentation

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Presentation version 1 – uploaded on 30 Apr 2020
  • CC1: Comment on EGU2020-604, Grace Pold, 04 May 2020

    Dear Adetunji,

    Your presentation was super interesting - thanks for sharing. I have two questions related to your work.

    First, do you think there might be a role for increased microbial diversity in explaining why the 5-15C diurnally fluctuating temperatures microcosms have similar levels of respiration to the constant 15C ones? Fluctuating redox can enable increased bacterial diversity, so perhaps there is increased niche complementarity under fluctuating temperature too?

    Second, given your hypothesis that time at 15C enabled alleviation of depolymerization as the rate-limiting step, what would your follow-up experiment to test this be? Do you think you could test this by repeating the diurnal temperature experiment with relatively less time at 15C and more at lower temperatures? Or can this information be extracted from the short-term incubations at 5, 10, and 15C?

    Thank you!

    Grace Pold

    • AC1: Reply to CC1, Adetunji Alex Adekanmbi, 04 May 2020

      Thank you so much for your comments. 

      I actually measured functional diversity of intracellular enzymes using microresp and did not see a difference among all the temperature treatments. However, there may be a difference in the genetic diversity or in the diversity of extracellular enxymes. 

      We carried out a follow up experiment with just the constant temperature incubations to see if prolonged incubation at a particular temperature dictates the potential of enzyme activity. We found that, the previous incubation indeed affect extracellular enzymes measured diffrently. 

       

      • CC2: Reply to AC1, Grace Pold, 04 May 2020

        Great - thank you so much for the clarification!

  • CC3: Legacy of past condicitons, Thomas Wutzler, 05 May 2020

    In line with your findings:

    In a similar study of oscillating temperature we observed a shift of microbial kinetics after a several weeks, but the timing of this shifts differed a lot across replictes, so it was hard to make inference. We hypothesize that we faced a legacy of a several-month-long storage of the soil before the experiement leading to acclimation of the community to low temperatures and reverting (in a non-determining) fashion to the experimental temperatures.

    Thiessen et al 2013:

     

    • AC2: Reply to CC3, Adetunji Alex Adekanmbi, 05 May 2020

      Thank you Thomas for this comment.

      I really appreciate your comment and the fact that we had similar approach.  I am looking at the paper at the moment, I hope to get back to you if there is any further question(s).