Simulating Temperature in a Soil Incubation Experiment

Laboratory soil warming experiments usually employ two or more constant temperatures in multiple chambers. By presenting a sophisticated environmental chamber, we provide an accurate temperature control method to imitate the magnitude and amplitude of in situ soil temperature and improve the experimental design of soil incubation studies.

This protocol will introduce a state of art environmental chamber and demonstrate a new method of a temperature control to improve the experimental design of a soil incubation. The main advantage of this technique is its capacity to imitate the magnitude and amplitude of institute soil temperature. This method can be applied to simulate the different warming scenarios in soil incubation, such as extreme heat.

One potential challenge of this technique is setting up the temperature profile in the chamber. Observing and understanding the diurnal temperature variations in the soil would be required. To begin, open the software on the computer and click on the Launch and Properties Toolbar button to configure the logger for the external sensors being used.

Set the logger station name and the data collection interval. Then on the Properties screen, click Enabled on the external sensor ports being used and select the sensor and unit from the dropdown menu for each sensor port. Finally, click on Okay to save the settings.

Download the data set once a month and obtain a complete record for several months covering the growing season. To analyze the data of the temperature records, obtain the mean hourly temperature of the growing season by averaging all observations. To obtain the mean temperature for each hour daily, average the temperatures on the same hour across all days during the growing season.

In the sophisticated chamber, launch the software and click on the Profile button on the main menu screen to create a new file. In the File Name Input line, enter SW Low. By clicking on the Instant Change option, enter 15.9 degrees Celsius as an initial temperature.

Enter two on the Minutes row to maintain the temperature for two minutes, and click the Done button. Then under the Ramp Time option, enter 15.9 degrees Celsius as the target set point and on the Hours row, enter 850 hours to sustain the temperature, click on the Done button. In the second chamber, add five degrees Celsius to each temperature node.

Create a new file name SW High and repeat the steps shown before. In the third chamber, add 23 additional steps corresponding to 23 observed hourly soil temperatures and at the last step called Jump, set 42 repeated loops. This leads to the scenario of gradual warming or GW Low.

In the fourth chamber, add five degrees Celsius to each temperature node and repeat the steps shown earlier. This will allow a simulation of varying temperatures for 42 days at a higher temperature level. conduct a preliminary run for 24 hours and output the temperatures recorded by the four chambers.

Plot the temperatures recorded by the chambers against those as programmed. If the temperatures achieved in the chamber match the temperatures as programmed by a temperature difference of less than 0.1 degrees Celsius during the 24 hours, the chambers are suitable for the soil incubation experiment. If the criteria were not satisfied, repeat another 24 hour test or seek a new chamber.

Near the temperature probe area, collect five soil samples at zero to 20 centimeter depth and put them into a plastic bag after removing the surface litter layer. Mix the sample thoroughly by twisting, pressing and mingling the materials in the bag until no individual soil sample is visible. Store the samples in a cooler filled with ice packs and transport the samples to the lab immediately.

Remove the roots in each core. Sieve it through a soil sieve of two millimeter and thoroughly mix and homogenize the sample. Weigh 10 grams of fresh soil.

Oven dry it for 24 hours at 105 degrees Celsius and weigh the dry soil. Derive the difference between fresh and dry soil samples and calculate the ratio of difference over dry soil weight to determine the soil moisture content in a spreadsheet. Weigh 10 grams of the field moist soil subsample and quantify the soil microbial biomass carbon by chloroform fumigation, potassium sulfate extraction and potassium per sulfate digestion methods.

Next, weigh one gram of the field moist soil subsample and measure soil hydrolytic and oxidative extracellular enzyme activity. Then weigh 16 field moist soil subsamples in 16 PVC cores sealed with glass fiber paper on the bottom. Place the cores in one liter mason jars lined with a bed of glass beads to ensure that the cores do not absorb moisture.

Place four jars in each of the four chambers. Turn on the chambers and launch the program simultaneously in four chambers. During the incubation, take all jars in each of the four chambers and put the color of the portable carbon dioxide gas analyzer on top of each jar to measure soil respiration rate.

Destructively collect all jars at the end of the incubation, that is on day 42, and quantify soil microbial biomass carbon and soil enzyme activity. Assuming a constant respiration rate between two consecutive collections, use the respiration rate times the duration to derive the cumulative respiration. Conduct a three-way repeated measures analysis of variance or ANOVA to test the main and interactive effects of time, temperature, and temperature mode on respiration rate and cumulative respiration.

In addition, conduct a two-way ANOVA to test warming and warming scenario effects on microbial biomass carbon and extracellular enzyme activity. The illustration of temperature change mode in a soil warming experiment is presented here. Constant temperature adopted by most studies, constant temperature with varying magnitude, linear change with positive and negative rates, and non-linear change with irregular and diurnal patterns are shown here.

The mean cumulative soil respiration rate under control and warming treatments in stepwise warming and gradual warming in a 42 day soil incubation experiment is shown in this figure. The insets show the soil respiration rates applied to estimate and cumulative respiration assuming a constant respiration rate. The results show that warming led to significantly greater respiratory losses in both warming scenarios and gradual warming doubled the warming induced respiratory loss relative to stepwise warming, 81%versus 40%The mean microbial biomass carbon under control and warming treatments in stepwise and gradual warming in a 42 day soil incubation experiment is presented in this figure.

Here, S denotes the significant effect of the warming scenario based on a three-way repeated measures ANOVA. This figure represents the mean hydrolases and oxidases activities under control and warming treatments in stepwise and gradual warming in a 42 day experiment. After it's a development, this technique paved the way for soil biogeochemists to examine effects of various warming scenarios on soil respiration and the micros by sophisticated programming in the chamber.