Lab 5: Soil and the Carbon Cycle
The lab activity described here was developed by Candace Dunlap of TERC for the EarthLabs project.
Use the button at the right to navigate to the student activity pages for this lab. To open the student pages in a new tab or window, right-click (control-click on a Mac) the "Open the Student Activity" button and choose "Open Link in New Window" or "Open Link in New Tab."
Investigation Summary and Learning Objectives
Students use animations and short videos to learn the basics of decomposition and microbial soil respiration and their relationship to the carbon cycle. They design and carry out a laboratory experiment on how soil respiration rates might be influenced by one of the following climate-related variables - temperature, soil moisture, soil nutrients, soil fertility, and soil type. Following that, they learn about permafrost, a frozen soil covering vast areas of the the Arctic and sub-arctic regions, that is beginning to thaw. They will consider possible carbon cycle feedback loops to a warming atmosphere if the permafrost continues to thaw.
After completing this investigation, students will be able to:
- Describe the role of soil respiration in transferring carbon from the soil to the atmosphere
- Describe the possible impact of a warming climate on permafrost
- Use systems thinking strategies to identify possible feedback loops between a thawing permafrost and the carbon cycle.
For more information about the TOPIC, read the section titled Background Information under Additional Resources below
In Part A: Students learn the basics of decomposition and microbial soil respiration and how these processes influence the carbon cycle. To better understand the impact of climate change on the carbon cycle, they investigate the effects of a change in an environmental variable (e.g. temperature, soil moisture, soil nutrients, etc) on microbial soil respiration using a simple soil respiration chamber and lime-water.
In Part B: Students learn the basics about permafrost soil and what might happen as this permanently frozen soil begins to thaw due to a warming atmosphere.
Printable MaterialsTo download one of the PDF or Word files below, right-click (control-click on a Mac) the link and choose "Save File As" or "Save Link As."
- Stop and Think Questions Lab 5A and 5B (Microsoft Word 2007 (.docx) 27kB Mar7 13)
- Suggested answers to Stop and Think questions: Lab 5A and Lab 5B with answers (Microsoft Word 2007 (.docx) 142kB Feb11 14)
Soil microbe respiration set-up.Teaching Notes and Tips
In Part A:
1. Think about having students do the first section on decomposition etc at home. After a brief class discussion, you can begin the microbial soil respiration experiment.
2. The inquiry-based "soil microbe" respiration experiment - important things to consider.
- This experiment reinforces the concept that it is microbes that are doing the respiring and not "soil" which is made of minerals, partially decomposed remains of living things (organic matter)water and air.
- To make sure that students understand the above, teachers should set-up a class controlusing soil that has been sterilized in a microwave. To do this, spread moist soil on a flat dish, and then heat it on high for two minutes or until it's steaming. Then set up one bottle with sterile soil and one with non-sterile soil. Safety tip: It is best not to let students do this.
- Most soil respiration experiments typically require harsh chemicals (ex. sodium hydroxide, HCL) and chemical titration to get quantitative measurements of respired microbial CO2. This lab is a qualitative lab - i.e. students will need to compare the cloudiness and amount of calcium carbonate precipitate in the limewater in their experimental jars/test tubes. It is OK if some results are inconclusive.
- Your role as Principal Investigator (PI). Students will come to you with experimental designs. If appropriate, guide them by asking questions. For example, how will you measure...? How can you be sure....? Would it be a good idea to use any of the soil meters or kits? Why?
- Based on their experimental design, some students may see discernible results the next day whereas others will not see results for 2-4 days.
- Some of the experimental variables are more complicated than others to do and some may need special equipment as part of their design (ex. lamps, refrigerator etc.). Eliminate variables you feel you cannot accomplish in your classroom.
- Some variables that are listed in the experimental protocol will have a more direct relationship to climate change and/or the permafrost section in Lab 5B. These include:
- Soil temperature
- Soil moisture (dry, moist, water-logged)
- Soil fertility and organic carbon (how much or type of organic matter decomposing in the soil)
- Soil nutrient availability* (N-P-K : nitrogen, phosphorus and sulfur)
- Soil oxygen availability (aerated soil versus compacted soil, moist soil versus water-logged)
Special Materials to order from school science catalogs such as Carolina Biological, Science Kit, Flynn etc.
- Glass apparatus tubing (5mm) - hollow
- Amber rubber tubing - 3/16th inch
- #4 one-hole stoppers
- Limewater is calcium hydroxide- Ca(OH)2 in solution. You can purchase limewater in liter bottles from any science supply company or make your own. Plan on at least a liter per class. Limewater has a limited shelf life of 1-2 years.
- Here is a recipe for limewater. http://www.hometrainingtools.com/making-limewater-solution-science-teaching-tip/a/1101/
- Soil testing kits and meters (optional but good to have) You will want to have a variety available(pH, moisture, soil temperature, soil nutrient N-P-K etc.) but let students figure out whether to use them or not. As the PI, you can guide them in these decisions. You can also purchase many of these at a garden supply store in addition to school science supply companies.
- Mycorrhiza (optional)- a soil fungus that is very important to providing plants with nutrients. Students may want to investigate whether Mycorrhiza will enhance soil respiration rates. Mycorrhizal products can be purchased from many on-line sources and in some garden centers.
You will find more specific teaching tips and explanations below. Tips are in bold italics.
- Soil temperature (Students may suggest refrigerators, lamps, freezers etc as part of their design)
- Soil moisture (dry, moist, water-logged) Water-logged soil and oxygen availability are linked. Water-logged or flooded soil environments include rice paddies, wetlands (swamps, marshes, and bogs); compacted soils; and post-rain soils. Water-logged soils often lead to anoxic (without oxygen) conditions because oxygen is only slightly soluble in water and diffuses much more slowly through water than through air. In lab 5-B, students will read about permafrost soil which is often water-logged. Anoxic conditions there favor a special group of bacteria (Methanogens) that produce methane instead of CO2 when they respire.
- Soil fertility and organic carbon (how much or type of organic matter decomposing in the soil) Students may suggest adding "compost" food such as banana and apple peels. They could eliminate the sugar and use plain water. As PI, you can bring this up and discuss.
- Soil nutrient availability* ( N-P-K: nitrogen, phosphorus and sulfur) *Note: Use a soil nutrient test kit to find soils outside that are low in nutrients. Fertilizer can be easily added to half of the soil to create high nutrient soil. Another possibility is to use Venus Fly-trap soil(low in nutrients). Students should test the low and high nutrient soilsthey will be using to ensure that the nutrient levels are indeed different.
- Soil type (sandy, clay, rich with humus, etc.)
- Soil oxygen availability (aerated soil versus compacted soil, moist soil versus water-logged) (Refer to soil moisture explanation above) Students can add perlite to aerate the soil and/or not compact it by tamping it down.
- Soil pH (acidic, alkaline, neutral) To change the pH, they will need to add chemicals to the water before they add it to the soil in the bottle. Baking soda, lime water etc will make the water (and thus the soil) alkaline. Diluted vinegar will make water and soil acidic. Students should definitely use a soil pH meter or if unavailable, pH papers.
- Other (for example, adding important soil fungi like mycorrhiza) Mycorrhiza are fungi that are essential to plant nutrition.
- Here is a recipe for limewater. http://www.hometrainingtools.com/making-limewater-solution-science-teaching-tip/a/1101/
- Safety alert! Lime water should be treated as a eye irritant. Safety goggles should be worn.
- Materials Safety Data Sheet for Limewater
Note: Don't forget to make the sterile soil versus non-sterile soil control ahead of time.
2. Fill the bottles approximately 1/3 to the top, add 20 ml of sugar water and then gently tap the bottle on the counter once to tamp down the soil.
3. Add more soil to 2/3 full and add 20 ml of sugar water. Tamp down the soil again.
4. Fill bottle with soil up to the cut rim. Add 20 ml of water. Close and seal the bottle with duct tape.
5. Insert the #4 one-hole stopper gas delivery apparatus into the bottle top. Insert the tubing into the test tube (or small jar) with the 50 ml of lime water. Make sure the end of the tubing is in the lime water. Use the aluminum foil to cover the test tube/jar.The collecting jar/test tube must be covered so CO2 from the air cannot dissolve in the limewater and the water in the limewater cannot evaporate. Both would bias the results and be sources of error.
6. Observing and Drawing a Conclusion: Make observations every day for the next few days. Look for tiny "flakes" of white calcium carbonate and/or cloudiness forming in the lime water. Stop the experiment when you feel you have enough experimental evidence to answer your research question. Plan for at least 2-5 days for results.
In Part B:
This section is fairly straight forward. Consider letting students examine samples of frozen soil, semi-frozen soil and thawed soil. If any students chose temperature's effect on soil respiration rates to carry out in the Lab 5A soil respiration experiment, they can become "experts" for the class and share their results.
Student notebooks are optional. Here are just a few suggestions for what to include in student notebooks for Lab 5:
Note: You may want to separate actual data collection and analysis into a Lab Notebook.
- Drawings and notes from videos, animations, discussions and activities
- Drawings of models and any revisions
- Notes, observations, drawings, and data from the soil respiration lab in Lab5A
Assessment:There are several options for assessments of students understanding of material produced in this Lab. Teachers can choose from the following list or create their own assessments.
- Assess student understanding of topics addressed in this investigation by grading their responses to the Stop and Think questions.
- Assess lab reports for the soil respiration lab.
- Assess permafrost feedback loop drawings in Lab5B
- Written Test for Lab 5 (Microsoft Word 2007 (.docx) 76kB Feb11 14) (Answer Key (Microsoft Word 2007 (.docx) 140kB Feb11 14)
State and National Science Teaching Standards
TO BE PROVIDED LATER
Developer will correlate activity to standards listed at this site:National Science Education Standards (SRI)
Background InformationBasics: Nature Scitable article on the basics of soil carbon storage
If you would like to learn more about soil and permafrost, here are several excellent on-line lectures:
Content ExtensionThese resources review how the new science of "metagenomics" is revealing new understanding of how microbial populations change with changing environmental conditions.
These resources are on changing agricultural practices to keep carbon in the soil. How the Soil Carbon Coalition is changing agricultural practices that will build carbon-rich soil This site has background information, videos, and links on initiatives to build carbon-rich soil.
If you live in a climate with seasonally frozen soil, try this Frost Tube Experiment. You can share data collected with other students at the GLOBE network.