Legacy effect of constant and diurnally oscillating temperatures on soil respiration and microbial community structure.
Raw data for the publication 'Legacy effect of constant and diurnally oscillating temperatures on soil respiration and microbial community structure' comprising respiration measurements, soil properties, and phospholipid fatty acid analysis of incubated soils. Abstract: Laboratory incubation studies evaluating the temperature sensitivity of soil respiration often use measurements of respiration taken at a constant incubation temperature from soil that has been pre-incubated at the same constant temperature. However, such constant temperature incubations do not represent the field situation where soils undergo diurnal temperature oscillations. We investigated the effects of constant and diurnally oscillating temperatures on soil respiration and soil microbial community composition. A grassland soil from the UK was either incubated at a constant temperature of 5 ℃, 10 ℃, or 15 ℃, or diurnally oscillated between 5 ℃ and 15 ℃. Soil CO2 flux was measured by temporarily moving incubated soils from each of the abovementioned treatments to 5 ℃, 10 ℃ or 15 ℃, such that soils incubated at each temperature had CO2 flux measured at every temperature. We hypothesised that, irrespective of measurement temperature, CO2 emitted from the 5 ℃ to 15 ℃ oscillating incubation would be most similar to the soil incubated at 10 ℃. The results showed that both incubation and measurement temperatures influence soil respiration. Incubating soil at a temperature oscillating between 5 ℃ and 15 ℃ resulted in significantly greater CO2 flux than constant incubations at 10 ℃ or 5 ℃, but was not significantly different to the 15 ℃ incubation. The greater CO2 flux from soils incubated at 15 ℃, or oscillating between 5 ℃ and 15 ℃, coincided with a depletion of dissolved organic carbon and a shift in the phospholipid fatty acid profile of the soil microbial community, consistent with the thermal adaptation of microbial communities to higher temperatures. However, diurnal temperature oscillation did not significantly alter Q10. Our results suggest that daily maximum temperatures are more important than daily minimum or daily average temperatures when considering the response of soil respiration to warming.
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The experiment was a 4 x 3 factorial design comprising of 4 incubation temperatures (5 ℃, 10 ℃, 15 ℃, or diurnally oscillating between 5 ℃ and 15 ℃) and 3 measurement temperatures (5℃, 10 ℃, and 15 ℃), with four replicates, resulting in 12 treatments and 48 units. Each week of the experiment the soil samples were incubated in controlled environment chambers for six days at their allocated incubation temperatures before moving to their allocated measurement temperatures 24 hours prior to respiration measurement, and then returned to their allocated incubation temperature after measurement of CO2 flux. Two blank (without soil) incubation jars were incubated at each measurement temperature as a blank to correct for background atmospheric CO2 concentration in the mesocosms and accounted for while calculating the CO2 flux. Four extra cores were both incubated and measured in an environment diurnally oscillating between 5 ℃ and 15 ℃. Measurements of CO2 flux were made when the environment was at 10 ℃ while the temperature was decreasing during the diurnal oscillation. The addition of this treatment meant that, at the end of the experiment, we had soils that had remained (without movement) at 5 ℃, 10 ℃, 15 ℃, and diurnally oscillating between 5 ℃ and 15 ℃ (representing 4 treatments, and 16 experimental units). These units were used for post incubation soil chemical and biological analysis. At the end of the experiment (after 17 weeks), soil samples were taken from the 16 containers that had remained (without movement) at 5 ℃, 10 ℃, 15 ℃, or diurnally oscillating between 5 ℃ and 15 ℃ for the entirety of the experiment to examine soil chemical and biological properties. A 10 g sub-sample of soil was extracted immediately for determination of available NO3- and NH4+. A further 5 g was used to determine the gravimetric water content and adjust the results of the NO3- and NH4+ analysis for soil moisture so that they could be expressed on a dry mass basis. A 5 g sub-sample was freeze-dried prior to phospholipid fatty acid (PLFA) analysis. A 15 g sub-sample was air-dried for chemical analysis to determine TC, TN, and hot and cold water extractable carbon (HWEOC and CWEOC).