1. Microbial Respiration in Soil Surrounding Aspen Trees
Maria Rocco
EBIO 4100: Winter Ecology: Spring 2012
"Mountain Research Station, University of Colorado, Boulder"
My name is Maria Rocco and today I will be discussing the levels of microbial respiration in soil surrounding aspen trees.
This research was done for a field research project for a course in Winter Ecology at the Mountain Research Station.
(for notes section of powerpoint: bold sections refer to areas directly on slides.)

2. Outline Background Hypothesis Methods Results Analysis Conclusions
Future Research
I will quickly outline what I will be covering today. I will start by providing some background research which has already been done in the field and the relevance my project plays into the understanding of winter microbial respiration. I will address the hypothesis I tested, discuss the research methods employed. Then discuss and analyze the results and end with conclusions drawn from the research and questions which came up during the analysis which could lead to future studies expanding the horizon of this project.

3. Background Seasonal Changes in Alpine Soil Community1
Changing populations throughout year, larger populations of soil microbes during winter months
Not only are populations larger but species diversity changes seasonally due to changing environmental considerations
Summer : Phototrophy
Winter: cold tolerant and rely on
cellulose
Macroinvertebrate Presence in
Soil with increased litter and
organic matter2
I will provide some background research which has already been done in this field.
Seasonal Changes in Alpine Soil Community: When discussing the variations in seasonal changes within the soil, a paper by Lipson and Schmidt illustrated the large variations in microbial biomass and available nitrogen, the diversity and population size of soil microbes changes seasonally as we discussed in class. Below is a graph we examined together illustrating the differences in microbe population throughout the year, with larger populations during the winter.
In addition to changing populations sizes, soil microbe diversity also changes, which when examined by schmidt and lipson makes sense as organisms that thrived during the summer months were similar and capable of phototrophy. During the summer months, where snow levels are low, light can more easily penetrate the soil, allowing microbes to utilize this source of energy.
Whereas during the winter months microbes cold tolerant and tend to rely on complex organic compounds such as cellulose, as these are more readily available than other sources of energy.
Macroinvertebrate Presence in Soil with increased litter and: as I will discuss shortly I originally was interested in studying macroinvertebrates and potential behavioral adaptations to cold climates. This study by Negrete Simoneta primarily dealt with human impacts on soil diversity and presence of macroinvertebrates, however the study yeilded a link between litter diversity,organic matter and the presence of macroinvertebrates. I will discuss the importance of this link in relation to my studies shortly. Simoneta discovered that as litter diversity increased macroinvert presence also increased.
Seasonal fluctuations of microbial biomass and available Nitrogen3

4. Background
Initial goal to examine presence of macroinvertebrates in soil, specifically looking at their presence in relation to tree growth and temperature gradients
CO2 flux primarily relates information about soil microbes
CO2 as a measure of soil respiration
Aspen trees
Higher N rich litter in aspen leaves
Overall Research Goal: Begin to examine possible behavioral adaptations of soil biota to winter environments
My initial goal was to examine the presence of macroinvertebrates in soil, specifically looking at their presence in relation to tree growth and temp gradients; however, after an initial field exercise it became apparent that the methods I was using would not yield enough information for analysis.
At that point I began looking into alternatives and ultimately decided to exam CO2 flux.
CO2 flux primarily relates information about soil microbes, as they account for most respiration in soil.
Microbes break down soil matter and litter, this in turn releases co2 and releases other nutrients back into the soil system. Micro and macro invertebrates then feed upon the microbes which release more N and CO2 and waste which can then be decomposed again by soil microbes. This food chain dynamic, results in an assumption that where there are larger populations of soil microbes there are also likely larger populations of soil macroinvertebrates as they feed upon each other and each others waste products. I therefore chose to exam soil respiration and the presence of CO2 in soil as an initial step to examining the presence and activity of macroinvertebrates in the soil.
Looking at aspen trees: I chose to specifically examine Aspens as their leaves have a higher N concentration and can be broken down more easily as compared to other trees active at these altitudes. The litter therefore beneath an aspen tree would likely have more nutrients and soil microbes decomposing the plant litter.
Overall Research Goal: Begin to examine possible behavioral adaptations of soil biota to winter environments, My overall goal is to analyze potential behavioral adaptations to winter environments, by determining if soil respiration and thus soil microbe and macroinvert presence increases in relation to plants.

5. Hypothesis
Soil temperatures further from the base of the tree will be colder than those closer to the trunk.
The rate of respiration decreases in soil further from an aspen tree.
Soil temperatures further from the base of the tree will be colder than those further from the trunk. This hypothesis was tested but did not reveal substantial results. From research it appears that small variations in temperature if they exist are masked but the overall temperature of the soil. Soil temperatures in winter are determined by the cold winter temperatures and are minimally if at all affected by tree root systems.
The rate of respiration increases in soil surrounding trees. As discussed on the previous slide, aspen littler has more readily available Nitrogen, from this knowledge, I predicted that as the distance from the trunk of the tree increases the amount of littler will likely decrease which will cause soil microbe presence to decrease and the rate of respiration to decrease as well.

6. Methods Measured 3 distances from Aspen Tree for five sites
Took measurements at ground level
Measured respiration rates and soil temperature using: Soil CO2 flux system
(X57/SRC1-CO2 FLUX)
In order to carry out the experiment I measured 3 distances from Aspen Tree for five different trees. The three distances that were measured were at the base of the tree, 10 cm from the tree base, and 1 m from the tree base. These distances were chosen to provide ample change in the amount of litter surrounding the tree.
Measurements were taken at ground level in order to prevent snow impacts on soil measurements. Respiration rates taken at ground level can then be directly linked to the soil respiration.
Respiration rates were taken using a Soil CO2 flux system, where the rate of change of CO2 within the chamber is measured.

7. Results Analyzing CO2 change as a function of time
Convert CO2 change to CO2 flux
Compare different trials looking for outlier data sets
Compare different distances from tree to see if CO2 flux changes with distance
The results obtained from the Soil CO2 flux system were recorded and converted to flux value as simple measurements of CO2 levels do not reveal all that much. This conversion was done using the known volume of the chamber and surface area of the entrance to the chamber as a function of time.
The different trials and distances from the tree were then compared.

8. 0 cm from Tree Trunk
This graph illustrates the data from the trials at the five trees closest to the tree trunk.
The Black Point well above all other data has been removed, a test for outliers within 3 standard deviations of the trend have been removed.

9. 10 cm from Tree Trunk
Although the black trial appears to be much higher than the other values, I will only be looking at the change in CO2 levels, thus the slop of this line fits with the others. However the green trial exhibits an unusual trend of decreases CO2, meaning CO2 is being taken up by the soil. This occurs in photosynthesis. There is possibility that this is taking place where soil depth is not enough to eliminate most light. This could be happening in the other trials also. However seeing as this trend appeared in only one of fifteen trials, for this analysis the green data was removed for these distances.
The possibility that photosynthesis is and could be taking place in soil, under snow during winter months, is a questions raised for future research.

10. Results
The results are shown in the chart, where the three lines correspond to the three distances from the base of the tree as seen on the x axis. The average CO2 from the different distances is shown on the y axis, with error bars corresponding to the standard error of the data. As you can see there is quite a bit of error and overlap between the sites.

11. Results
This plot illustrates the differences between the average flux rates between the 0 and 10 cm site and the 10 cm and 100cm site. These differences are slightly more substantial however they are not significant, with the amount of data collected.
The trend however is the difference in flux is negative for values between 0 and 10, meaning values at 10cm in general have more respiration occurring than those at the base of the tree trunk.
The difference between the 100 and 10 cm distances is positive implying that more respiration occurs at 10 cm than 100cm.

12. Analysis
Appears to be no significant difference between the distance from tree and soil respiration.
Analysis on a larger scale may be necessary as root systems may extend further from the tree than 1 m
This may have been a large contributing factor as aspen root systems are very extensive.
Overall the analysis revealed no significant results. This may change is research is done on a larger scale, collecting samples from more than the 5 aspens.

13. Conclusions/Future Questions
What components of the soil microbes/macroinvertebrates’ genome deal with extreme temperatures and cold tolerance?
The possibility that photosynthesis is and could be taking place in soil, under snow during winter months
What other factors play a role in macroinvertebrate and microbe presence in the winter?
Tree type
Root systems?
Moisture levels?
Aspect?
What components of the soil microbes/macroinvertebrates’ genome deal with extreme temperatures and cold tolerance?
What genetic components actually allow these organisms to survive and thrive through winter, is a specific gene responsible for cold tolerance, is this the same gene responsible for cold tolerance in other invertebrates and similar to those in mammals?
As brought up earlier there is a possibility that photosynthesis is taking place in soil under snow during winter months. Is this likely or common in alpine soil communities?
We performed an experiment as a class to determine how snow depth correlates soil respiration, it would be interesting to expand this study and look at respiration rates in response to tree type, moisture gradients, aspect, snow depth, and ground temperature gradients. And further look into the presence and activity of macroinvertebrates in relation to each of those parameters.

14. References
1Lipson, D. A., and S. K. Schmidt. "Seasonal Changes in an Alpine Soil Bacterial Community in the Colorado Rocky Mountains." Applied and Environmental Microbiology 70.5 (2004): Print.
2Negrete-Yankelevich, Simoneta. "Integrating Soil Macroinvertebrate Diversity, Litter Decomposition and Secondary Succession in a Tropical Montane Cloud Forest in Mexico." Global Change Research Institute PhD Thesis Collection (2004).Edinburgh Research Archive. Web. 24 Feb <
3Schmidt, S.K. and D.A. Lipson Microbial growth under the snow; Implications for nutrient and alleochemical availability in temperate soils. Plant and Soil 259: 1-7. 
References used.

15. Questions?