Effects of Temperature on Respiration Rate of Microorganisms in Organic Soil, Research Paper Example

Introduction

Eukaryotic and prokaryotic organisms are dependent on oxygen in order to survive. In the soil habitat, there are different types of both eukaryotic and prokaryotic organisms that live and require energy that is obtained through aerobic respiration. Respiration in soil occurs from root respiration and the decomposition of organic matter, plant litter and root exudates created from microorganisms living in the soil. (Blongquist Jr. et. al) Some microorganisms living in the soil, therefore, require oxygen (O₂) in order for oxidation-reduction reactions to occur as well as aerobic respiration. If the concentrations of O₂ are low, other forms of respiration occur, such as fermentation. The rate of respiration in organisms is also dependent on physical factors, such as temperature. Temperature is considered one of the most important environmental factors that affect microbial growth and activity in soil. In addition, understanding changes in temperature dependence in soil microorganisms is important because they produce Carbon Dioxide (CO2) in the decomposition of organic matter in the soil. (Pietikåinen et al., 2006) Microorganisms living in the soil can be affected by changes in temperature. Some of the microbial enzymes in microorganisms require oxygen, and the level of oxygen regulates enzymatic activity. Increases in temperature can alter enzyme activity. For instance, increased temperatures can denature enzymes. (Pietikåinen et al., 2006) If this occurs, microbial enzymes in microorganisms will not function properly. Changes in temperature in soil microorganisms, can therefore, be studied through measuring the respiration rate.

In this experiment, the effects of temperature on soil respiration were examined. It was hypothesized that changes in temperature would produce a change in the rate of respiration in the organic soil. It was predicted that an increase in temperature would increase the rate of respiration to a certain point and the rate would decrease due to excessive heat disrupting enzymatic activity.

Methods

An electrochemical O₂ gas sensor (Vernier Software, www.vernier.com) was used to measure the O₂ consumption of gas in organic soil. Two treatment groups and one control were used with three trials for each group. The control group was exposed at room temperature at 20-25 °C. The first treatment group was placed in a water bath at a temperature of 10 °C. The second treatment was placed in a water bath at a temperature of 30°C. After a set amount of time, the O2 was measured with the gas sensor. The gas sensor was placed into the reaction chamber and data was collected, saved and recorded. A minimum, maximum and median temperature was recorded for each trial during each treatment group. An ANOVA was completed in order to compare the control versus the treatment groups. A correlational analysis between the oxygen level and time of the experiment was completed in order to compare any effect of time on the oxygen level.

Results

The results of the experiment illustrate a change in respiration during each treatment. The mean oxygen level at 10°C was 17.79 (Table 1). The mean oxygen level at room temperature was 18.42 (Table 1). The mean oxygen level at a 30°C was 17.88 (Table 1). The results were not significantly different, the p-Value for both the cold and hot temperature versus room temperature was not <0.05 (Table 1). The minimum and maximum oxygen level values for each treatment group was also recorded (Table 2). The treatment group with the lowest minimum oxygen level was found during the 30°C treatment (Table 2). The maximum oxygen level was found during the control treatment at room temperature (Table 2). The correlational analysis conducted between the oxygen level and time during each treatment for each trial was also completed (Figures 1, 2, 3, 4, 5, 6, 7, 8, 9). There was no correlation between the time and oxygen level.

Discussion

Temperature effects on the respiration rate of organic soil varied between treatment groups. The oxygen level was at a minimum during the increased temperature of 30°C (Table 2) and was at a maximum during control treatment at room temperature (Table 2). The results, however, were not significantly different when comparing the means between the treatment of 10°C and room temperature and 30°C and room temperature (Table 1). Therefore, there was no major difference in oxygen (O2) levels between each of the treatment groups studied. This contradicts previous literature findings where the respiration rate of soil had a significantly higher rate at room temperature (Persson et al., 1999). It is possible that the experiment was not run at a long enough time. Perhaps the time for analysis should have been greater than 200 seconds. In addition, the temperature differences may not have been high enough. The variance between the cold and hot temperatures should have been greater. For instance, instead of 10°C, the cold temperature should have been brought to freezing. It would have been a good idea to compare a freezing temperature and effects of oxygen levels in the soil as this occurs during winter months. It was noted that the incubation time for a high temperature was to be kept at a minimum in order to avoid the growth of thermophilic communities. However, it has been previously studied that a respiration technique at a time of 5 hours at 45°C is sufficient for a study of the temperature effects of oxygen in soil. (Pietakinen et al., 2006).

The correlation analysis in the figures is also exhibited. The comparison between time and oxygen level does not show a significant comparison as the values are not close to 1. As mentioned previously, perhaps the time during trials should have run longer in order to obtain more accurate results of the oxygen levels over time.

Although the present study does not give significant differences between the means of the oxygen levels between the control and treatment groups, the actual values do show that there was some difference when the temperature was altered. For instance, the mean oxygen level during the 10°C treatment was 17.79 and the mean oxygen level during the 30°C treatment was 17.88, compared to the control group at 18.42. There is a clear decrease in respiration seen at the decrease and increase in temperature versus respiration rate. It was hypothesized that an increase in temperature would increase the rate of respiration to a certain point and then decrease due to excessive heat. As seen in Figure 7, 8, and 9, the respiration rate actually decreased during the trial, but increased towards the end of the trial. This does not support our hypothesis. It was thought that after exposed to increased temperatures, microorganisms living in the soil would not respire due to the denaturing of enzymes from the heat. The temperature of the treatment group was therefore, not high enough during this experiment.

Microorganisms found in the soil usually consist of bacteria and protozoa. These types of organisms are not considered either ectothermic or endothermic. They do, however, respond to changes in the environment and depend on plants and fungi in order to obtain their nutrition. Changes in oxygen levels in the soil, therefore, can have an adverse effect on their survival, as changes in oxygen levels can affect plants and fungi. During this experiment, there was a notable change in respiration rates at both an increase and decrease in temperature. To further evaluate the change, additional studies examining the actual microorganisms should be evaluated. Perhaps cultures of microorganisms should be placed in soil at different temperatures and the rates of respiration and growth should be evaluated in order to see an actual effect of temperature.

Table 1. Mean Oxygen (O₂) levels for each treatment of organic soil. ANOVA performed between the control group and each treatment group is represented by the P-Value. A P-Value <0.05 would indicate a significant difference.

Table 2. Minimum and Maximum Oxygen (O2) levels during the trials for each treatment group.

References

Blonquist, J.M. Jr., Jones, S.B., Bugbee, B. Estimation of Soil Respiration: Improved Techniques for Measurement of Soil Gas. Apogee Instruments, Inc. 30 pgs.

Persson, T., Breland, T.A., Seyferth, U., Lomander, A., Kåtterer, T., Henriksen, T.M., Andrén, 152. (1999) Carbon and nitrogen turnover in forest and arable soil in relation to substrate quality, temperature and moisture. Tema Nord 560, 131–152.

Pietikåinen, J., Pettersson, M., Baath, E. (2006). Comparison of temperature effects on soil respiration and bacterial and fungal growth rates. FEMS Microbiology Ecology. 52(1): 49-58.