Climate Change Experiment LAB — Questions

Overview

Educated citizens need to understand how scientific investigations are done and how results and conclusions are reported in order to make informed decisions. What is experimental evidence? What is hypothesis testing? How do scientists evaluate data and draw conclusions? Educated citizens also need a basic understanding of climate change. In this lab, we are going to watch a video fieldtrip of the Asymmetric Warming Experiment at the Environmental Protection Agency (EPA) in Corvallis, which uses precision climate-controlled chambers called “terracosms”. After watching the video, you will answer questions to help guide you through understanding how the experiment was designed. The purpose of this lab is to refresh your memory and understanding of the scientific method and ecology while learning how scientists study climate change.

BE ORIGINAL! Remember to use your own words and do not copy verbatim from any online, previous or current student source. By submitting this assignment, you are agreeing to the following statement: “I understand that my paper will be checked against multiple sources for original content. A report will be generated that shows if content in this paper matches content in documents available on the Internet, in many print journals, and a database of other papers submitted by students. If submitted to the instructor, my paper will be added to the student database for comparison of future OSU papers against it. I maintain ownership of the original intellectual property created in this paper. I understand that results of this report may be used by the University in student conduct proceedings related to academic dishonesty (See Canvas Start Here module for more information)” Turnitin generates a report that highlights any potentially unoriginal text in your paper, including text from previous students’ or current students’ submissions.

Assignment

Watch the virtual field trip to EPA terracosms, and use the information to answer the questions below.

Link to virtual field trip:

https://courses.ecampus.oregonstate.edu/index.php?video=soil102/terracosm_fieldtrip.mp4

Last modified August 7th, 2018

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Reflection (2 pts)

Reflect back on last week’s work. Please use complete sentences!

a) Identify one thing you did well. Be specific and use an example.

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b) Identify one thing you could improve upon. Be specific and use an example.

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Part 1: Hypothesis Development (21 Points)

1.1 (3 pts) Refer back to the lab background and field trip video to answer the following questions. Figure 1 may be helpful.

a) Describe what is asymmetric warming.

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b) Describe what is symmetric warming.

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c) How are they different from each other? How are they similar?

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1.2 (2 pts) Use Figure 1 to answer the following questions. 

Figure 1. Terracosm air temperatures over a 24-hour period from 6am – 6am.

a) Which of the warming treatments is warmer in the afternoon (noon – 6pm)?

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b) Which of the warming treatments is warmer at night (midnight – 6am)?

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Photosynthesis tends to increase with warming up to an optimal temperature, and then decrease with additional warming (Figure 2). Respiration does not have a temperature optimum; it tends to increase exponentially with temperature (until a plant becomes stressed or dies; Figure 2). 

Figure 2. Temperature response curves for photosynthesis (P) and respiration (R).

The balance of photosynthesis and respiration affect how much a plant grows. If a plant can photosynthesize more carbon than it respires, it will have a surplus of carbon it can use to make new tissue. But if a plant respires most of the carbon it photosynthesizes just to maintain its current tissue, it cannot grow more. Thus, if a plant can increase photosynthesis and not increase respiration, it will grow more. However, if respiration increases and photosynthesis does not, it will grow less.

Consider another scenario as a metaphor. If a human child gets enough food (photosynthesis) to support their activity level (respiration) they will grow normally. However, if their activity level increases (respiration) without also increasing food intake (photosynthesis) they will not grow. In plants, temperature affects their rate of food intake (photosynthesis) as well as ‘activity’ (respiration). If temperature increases too much, photosynthesis cannot make up for the losses due to respiration.

In the following section, you will be asked a series of short questions in order to guide you into answering the following, more in depth question.

1.3 (4 pts) Warming in the morning

a) What temperature is typical at 7a in the morning? (Figure 1)

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b) When temperatures are low (< 10oC), does photosynthesis or respiration increase faster (Figure 2)?

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c) Would a temperature increase from 5 to 10oC in the morning (6a-noon) lead to a greater increase in photosynthesis or in respiration?

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d) If global warming is causing the largest temperature increases to occur in the morning (i.e., the cooler part of the day), would you predict plants to grow more, less, or the same amount compared to their growth before warming?

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1.4 (4 pts) Warming in the afternoon

a) What temperature is typical in the afternoon (noon-6p)? (Figure 1)

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b) When temperatures are high (i.e., 25oC) does photosynthesis or respiration increase faster (look carefully at the photosynthesis curve in Figure 2)?

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c) Would a temperature increase in the afternoon (from 20 to 25oC) when temperatures are high lead to a greater increase in photosynthesis or respiration?

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d) If global warming is causing the largest temperature increases to occur in the afternoon (i.e., the hottest part of the day), would you expect plants to grow more or less than they did before warming? Explain your prediction.

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1.5 (3 pts) Warming at night

a) What temperature is typical at night (midnight-6a; a range is fine)?

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b) Would both photosynthesis and respiration respond to a temperature change at night? Consider carefully whether both photosynthesis and respiration occur at night.

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c) If global warming is causing the largest temperature increases to occur at night, would you expect plants to grow more or less than they did before warming? Explain your prediction.

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1.6 (3 pts) Formulating hypotheses

Below are the three alternative hypotheses that Dr. Jillian Gregg tested in the Asymmetric Warming study. Provide at least one reason each hypothesis might be expected to be true, based on your responses above. Consider how temperature affects both photosynthesis and respiration.

a) Hypothesis 1: Plants will grow more under asymmetric warming than under symmetric warming.

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b) Hypothesis 2: Plants will grow less under asymmetric than symmetric warming.

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c) Hypothesis 3: Plants will grow similar amounts under asymmetric and symmetric warming.

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1.7 (2 pts) A hypothesis is different from an ordinary prediction because it is both testable and falsifiable.

a) Explain how the hypotheses above are testable.

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b) Explain how the hypotheses above are falsifiable.

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Part 2: Experimental Design (11 Points)

Figure 3. View of the 12 terracosm chambers.

2.1 (2 pts) Jillian Gregg decided that the best way to test between her hypotheses was with an experimental study. What are the key differences between an experimental study and an observational study (note that you make observations in both…)??

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2.2 (3 pts) Identify:

a) which treatment was the control group in the experiment?

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b) which treatment or treatments was a manipulated group in the experiment?

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c) which variable was manipulated in the asymmetric warming study?

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2.3 (2 pts) Replication is critical for any experimental study. In this experiment:

a) How many replicates were there for each group?

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b) Why is it important to have replication in this experiment?

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2.4 (2 pts) The hypotheses listed above are only concerned with comparing asymmetric and symmetric warming. Explain why you think Jillian Gregg included the ambient terracosm chambers.

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2.5 (2 pts) If you were to develop an observational study to test Jillian Gregg’s hypotheses, how might you go about it? Note: do not say that you would observe the chambers. Make sure your answer here is consistent with your answer in 2.1, above.

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Part 3: Ecology (12 Points)

Figure 4 shows Jillian constructing the terracosm soils, and the grasses and wildflowers shortly after they were transplanted from the green house. Any ecological experiment involves trade-offs: the more controlled an experiment is, the more certain one can be that differences between groups are from the experimental manipulation and not just from natural variability, but the less confident one is that the results are relevant to real-world conditions. Jillian Gregg indicated that terracosms are more realistic than manipulating potted plants in growth chambers.

Figure 4. The terracosm chambers during the construction process. Left: filling the belowground compartments with soil and buring soil moisture sensors. Right: transplanted seedlings during the first year.

3.1 (3 pts) Identify at least three things about the terracosms that make them more realistic than potted plants grown indoors.

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3.2 (3 pts) Name at least three features of the terracosm that made this study more artificial, and less ecologically realistic, than a completely open environment.

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Figure 5 shows plant size (as indicated by leaf area index (LAI)) of each treatment over six years. In 2012, growth was limited because the spring was unusually cool.

Figure 5. Plant size indicated by leaf area index (LAI), 2007-2012. NS means there was no statistical difference between the treatments. Letters a,b,c indicate treatments that were statistically different. In 2010 the two elevated temperature treatments had more leaf area than ambient but were not different from each other. In 2011-2012, all three treatments were different from each other.

3.3 (3 pts) Consider Figure 5 to answer the following questions.

a) Do you think this system is reaching a stable (equilibrium) state, or do you think that it is still unstable and unpredictable due to all the disturbance caused by creating the chambers?

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b) What do you see in the graph that supports your reasoning?

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c) Why would that indicate either a stable or unstable condition? (Note: There is more than one right answer here; simply explain your observations and reasoning.)

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3.4 (3 pts) What is the appropriate scope of inference of this experiment? In other words, how far can we generalize the results–Can we generalize beyond the terracosms to grasslands of the Willamette Valley? To all grasslands? To all natural ecosystems?

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Synthesis and Relevance (4pts)

In climate change science and policy, the concept of resilience is gaining importance. Put simply, resilience is the ability to maintain key functions and essential stability despite profound disturbance; in essence it is the tool that enables a system to be sustainable. Reflect on the concept of resilience as you answer the questions below:

a) One solution proposed for preserving species threatened by climate change is to physically relocate them to more favorable areas as their native range becomes uninhabitable. Do you think the terracosm experiment indicates Willamette Valley prairies will need to be relocated, or will be resilient to projected climate change? Explain, referring to specific elements of the experiment and data you saw above.

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b) Willamette Valley prairies are imperiled, even without climate change, and are actively managed for threatened and endangered species. Climate change resilience includes the idea that we need a diverse ecological landscape to maintain ecosystem services we depend upon as the climate system changes, these prairies being one example. Can you name three ecosystem services these prairies provide that may help human communities be more resilient to climate change?

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