Scientific Paper

Introduction: (Total: 10 pts)
1. Transpiration is critical for plant physiology. In your own words, what is transpiration, and why is this important in plants? (2 pts)
Transpiration is the evaporation or loss of water through the pores (stomata) on the underside of leaves. Transpiration is vital to plants because it not only allows the plant to cool itself, but it also changes the osmotic pressure of cells allowing for nutrient transfer between cells, and between roots and stem.
2. Plants can respond to abiotic factors and alter their transpiration accordingly. How do plants regulate transpiration (cite primary literature here!)? (2 pts)
Plants are able to regulate the rate of transpiration that takes place through the use of pores called stomata. When the stomata are opened rates of transpiration are generally high, however if they close their stomata transpiration declines or even stops. Plants are able to control the whether their stomata are opened or closed with the use of guard cells, which surround the stomata. Plants open their stomata only when light intensity is sufficient to maintain a moderate rate of photosynthesis. Therefore they generally keep their stomata closed at night because no CO2 is need at night (Sadava et al., 2009).
3. Many abiotic factors can affect transpiration rate. List these factors, and talk more specifically about the ones we tested in class and how surface area affects transpiration. Then go into even more detail about the specific abiotic variable you tested with statistics. What have other researchers previously found out about these factors that you selected? (cite scientific primary literature here!) (4 pts)
Of the various factors that have the ability to affect transpiration rates we studied three specifically, heat, humidity, and closure of stomata. The humidity test that we ran in lab demonstrated that during periods of higher humidity the plant transpired less water than during the control, this was due to higher water content on the outside of the plant. During an experiment preformed by (Kuwagata et al., 2012) it was shown that the daily transpiration rates of plants grown at low humidity levels were 1.5 to 2 times higher than those same plants at high humidity levels. The heat test showed that during periods of increased heat transpiration rates increased. Yamaoka (1958) studied the relationship between transpiration and meteorological elements and also determined that transpiration rates were higher on days when the light intensity was higher. When testing how the closure of stomata affected transpiration our experiment showed that with the stomata closed transpiration was greatly reduced. Surface area was the final factor that we took looked at as having an affect of transpiration. According to our data the larger the surface area of a plant the higher the rate of water uptake. De Rocher and Tausch (1995) who were predicting potential transpiration of singleleaf pinyon found that water uptake was positively related to the total crown needle surface area.
4. Hypothesis: In the laboratory, you were asked to determine three hypotheses (predictions) for three factors that you selected to test and surface area. Re-write these four hypotheses and explain the rationale for each one. (2 pts)
Heat: An increase in the heat should lead to an increase in water loss because at higher temperatures plants that are not specialized to high heats will experience higher rates of evaporation of water from their stomata.
Humidity: Increased humidity will cause little to no change in the in the amount of transpiration a plant experiences because the amount of moisture outside the plant will be similar to the moisture levels inside the plant.
Closed stomata: Water loss will be greatly reduced because the closing of stomata will not allow transpiration to take place.
Total surface area vs. water loss: The greater the surface area plant has the greater the water loss it will experience, this is because it will have a greater number of stomata and therefore more places for transpiration to take place.
Material & Methods: (Total: 5 pts)
1. What is the potometer measuring? How does this relate to plant physiology? (See your textbook (pp 739-753). (1 pt)
The potometer was used to measure the rate at which the plant, Iresine herbstii (Bloodleaf), drew up water. This is related to plant physiology because as the water is transpired out of the leaves, the root, or in this case the end of the stem, must take up water to distribute it throughout the plant to make up for the recent water loss.
2. Describe your potometer set-up and state exactly how you assessed the three abiotic factors selected. (2 pts)
The potometer set up included multiple parts all working together. First you must fill a plastic tube with water. On one end of the tube the Bloodleaf cutting was inserted and sealed air-tight. On the other end of the tube a calibrated pipette was inserted and used to measure the amount of water the plant took up after each of the three abiotic factors were tested.
The amount of water taken up was measure in ml/g. The amount of water up take in the Bloodleaf resulting from excessive heat was measured by first taking an initial potometer reading after letting the control equilibrate for two minutes. Then a 70-watt light bulb was placed 10cm away from the leaves. After ten minutes of excessive heat the light was turned off and the potometer was measured again to find the difference (water up take).
After again letting the system equilibrate for two minutes after the heat test it was time to begin the humidity test. This was done by placing a plastic bag over the blood leave, spraying four full sprays of water into the bag and then sealing it around the plant. After spending ten minutes inside the bag was removed from the plant and another potometer reading was taken. The plant leaves were moist directly after this experiment.
Yet again after the humidity experiment the system was given to minutes to equilibrate before starting the closed stomata experiment. To measure the water up take takes place when stomata are closed we covered the leaves in petroleum jelly. After waiting ten more minutes we then took another reading from the potometer and calculated the water that was taken up by the plant.
3. Briefly state the two statistical tests you used and what alpha level you used for your statistical significance (p = 0.05 is standard). You do not need to talk about the F-test; simply state which T- test you used and the results of your F-test will be obvious! (2pts). The proper way to state this information is as follows: To determine if humidity decreases the rate of transpiration in Iresine leaves, a two-sample t-test was used (α = 0.05). Please do not write "I used the t-test to analyze these data."
Results: (Total: 15 pts)
1. Create a bar graph that depicts the results of the potometer measurements with one comparison (e.g. one treatment of your choice vs. the control). Make sure your graph is labeled correctly on the x and y axis, and give it a title that reflects what is happening in the graph (i.e. “Exposure to dry soil increases water uptake”). It should also have a legend and the correct units on each axis. (5 pts). If you are reporting means, you must also use either standard deviation bars or standard error bars (and you should know the difference and which one to use).

You should also make a scatter plot of your leaf surface area vs. water loss and have all of the appropriate parts. (5 pts)

2. What was measured, and what were the results for the treatment you chose and the surface area results? Describe what you found including your statistics (p-values for both analyses). Remember, there should not be any interpretations or explanations in this section. This section simply states what you found while running your experiment and analyzing your data (5 pts).
Throughout the experiment four different variables were measured, transpiration due to heat, transpiration due to humidity, transpiration due to closed stomata, and surface area. The mean and standard deviation of each of the variables were respectively found to be as follows, control =0.047 + 0.036; heat =0.041 + 0.023; humidity =0.021 + 0.021; closed stomata =0.030 + 0.021; surface area =97.16 + 21.08. P-values for both analyses were found to be insignificant (p>.05).
Discussion: (Total: 15 pts) 

1. Summary:
Briefly state, and then examine what you found for the treatment you examined and also for the surface area. Then talk about the other treatments and whether one had more significant results than others and WHY. This is where you want to explain your results. Do not simply restate them! (3 pts)
In closer examination of the humidity test it was found that on average the amount of transpiration was reduced by half during the experiment in comparison to the control rate of transpiration. 
Total surface area, shown in the graph above, was, for most groups, directly proportional to the rate of transpiration. With examination of the remaining treatments it can be seen that heat had almost not change in transpiration rate compared to the control (on average), while the closed stomata data set shows a large drop off of transpiration rate. The results may be seen as such for various reasons. I believe that there may be some discrepancies in some of the data sets, which lead to inaccurate numbers. All of the results from the class data result in conclusions that agree with previously obtained data, with the exception of our heat experiment.
2. Limitations of study:
a. Do you think that water uptake equals the transpiration rate of the plant? Why or why not? (1 pts)
b. What are the limits of the potometer in measuring transpiration rate? (1 pt)
c. You used Iresine leaves in this experiment. How might leaf sizes, textures, and shapes lead to different results (use and cite primary literature here)? (1 pts) 

Water uptake does equal the transpiration rate, this simple statement can be proven with the simple fact that if water uptake did not meet or exceed the transpiration rate the plant would die due to lack of water. “The water uptake patterns of Aloe marlothii, Aloe davyana and Portulaca quadrifida are similar to those of the daytime transpiration water loss but shifted towards nighttime” (Ruess et all., 1988). A limit of the potometer method is that the potometer does not measure the rate of transpiration accurately because not all of the water that is taken by the plant is used for transpiration some water taken may be used for photosynthesis or by the cells to maintain turgidity. Leaf sizes, textures, and shapes my lead to different results, as shown by De Rocher and Tausch (1995), “water uptake from the potometer was positively related to both the foliar mass plus the average number of resin canals in the needles of each tree”.
3. Comparison to other studies: (5 pts)
How do these differences in leaf morphology reflect differences in native habitat (climatic conditions)? You will want to use references here. 

Plants that live in extreme conditions tend to be specialized to live in that specific environment. Savada (2009) describes xerophytes, which are plants that have adaptations that allow them to live in extreme heat. Xerophytes have a thicker cuticle, specialized leaf anatomy that reduces water loss and are able to diffract and reflect sunlight by trichomes. All of these morphologies around found on plants that live in an environment that is hot enough that they are needed for survival.
4. Overall conclusions: (4 pts)
State your overall conclusions of what you learned and list three ways that the experiment could be improved.
This experiment showed the different ways in which different abiotic factors, including heat, humidity, and closed stomata can affect transpiration rate. It was shown how high humidity and closed stomata decrease the rate of transpiration while high heats, along with increased surface area increase the rate of transpiration. This experiment would be improved by allowing the plants more time to equilibrate in between each experiment. It would also be advantageous if we were able to preform the experiments over longer periods of time on larger populations. One final way that the experiment could be improved upon is by using a variety of plants to compare the effects on transpiration rate between plant species.

Citations
DEROCHER, TR., TAUSCH, RJ; 1994. Predicting Potential Transpiration of Singleleaf Pinyon-An Adaptation of the Potometer Method. Forest Ecology and Management. 63:169-180

Kuwagata, T., Ishikawa-Sakurai, J., Hayashi, H., Nagasuga, K., Fukushi, K., Ahamed, A., Takasugi, K., Katsuhara, M., Murai-Hatano, M; 2012. Influence of Low Air Humidity and Low Root Temperature on Water Uptake, Growth and Aquaporin Expression in Rice Plants. Plant and Cell Physiology. 8:1418-1431

Ruess, B R., Eller, B M., Ferrari, S; 1988. Transpiration and Water Uptake of Succulents in Their Natural Habitat Field Determinations With a Potometer. Botanica Helvetica. 98:215-222

Sadava, D., Hillis, D M., Heller, H C., Berenbaum, M R. 2009. Life the Science of Biology (9th ed.) Sinauer Associates, Inc., Sunderland, MA.

Yamaoka, Y. 1958. Experimental Studies on the Relation Between Transpiration Rate and Meteorological Elements. Trans Amer Geophys Union. 39:249-265

Citations: DEROCHER, TR., TAUSCH, RJ; 1994. Predicting Potential Transpiration of Singleleaf Pinyon-An Adaptation of the Potometer Method. Forest Ecology and Management. 63:169-180 Kuwagata, T., Ishikawa-Sakurai, J., Hayashi, H., Nagasuga, K., Fukushi, K., Ahamed, A., Takasugi, K., Katsuhara, M., Murai-Hatano, M; 2012. Influence of Low Air Humidity and Low Root Temperature on Water Uptake, Growth and Aquaporin Expression in Rice Plants. Plant and Cell Physiology. 8:1418-1431 Ruess, B R., Eller, B M., Ferrari, S; 1988. Transpiration and Water Uptake of Succulents in Their Natural Habitat Field Determinations With a Potometer. Botanica Helvetica. 98:215-222 Sadava, D., Hillis, D M., Heller, H C., Berenbaum, M R. 2009. Life the Science of Biology (9th ed.) Sinauer Associates, Inc., Sunderland, MA. Yamaoka, Y. 1958. Experimental Studies on the Relation Between Transpiration Rate and Meteorological Elements. Trans Amer Geophys Union. 39:249-265