Collaborators:
David Delgado, Brandon Garff, Sona George and Hailey Hendriks.
David Delgado, Brandon Garff, Sona George and Hailey Hendriks.
Introduction & Problem:
NPP, or net primary productivity, can be defined as "the total amount of chemical energy (glucose) created from the sunlight an area receives minus how much carbon dioxide the plants release during [cellular] respiration" (NASA). This quantitative information offers a way to study the condition of ecological processes in an ecosystem. Most importantly, it allows scientist to analyze the factors that affect the production potential of plants, including climate change, soil moisture, "plant community composition, the microenvironment, and resource availability"(Pantel, A. Romo, J. T., & Bai, Y.). Thus, NPP is a measurement that can convey the health of an ecosystem, as well as the effect that human activities have on a habitat's ability to support life. However, analyzation in this experiment depends on the obtained NPP of fescue plants, which can then be compared to the known value in order to draw more conclusions regarding the environmental factors that impact NPP. For this reason, the problem being addressed in this lab is "What is the NPP of fescue plants," which can be calculated by dividing the biomass of the grass clippings by the area of the opening of the bottle by the amount of days the grass was allowed to grow.
Hypothesis:
If fescue seeds are planted and allowed to grow for six days, then the NPP of the grass will be lower than the known NPP of fescue plants -- 58 g/cm2/year -- because of the limited amount of energy that a lamp can input into the system as compared to natural sunlight.
Parts of the Experiment:
Materials & Methods:
a) Materials:
b) Method:
Lab Day 1:
Data & Data Analysis:
a) Data:
NPP, or net primary productivity, can be defined as "the total amount of chemical energy (glucose) created from the sunlight an area receives minus how much carbon dioxide the plants release during [cellular] respiration" (NASA). This quantitative information offers a way to study the condition of ecological processes in an ecosystem. Most importantly, it allows scientist to analyze the factors that affect the production potential of plants, including climate change, soil moisture, "plant community composition, the microenvironment, and resource availability"(Pantel, A. Romo, J. T., & Bai, Y.). Thus, NPP is a measurement that can convey the health of an ecosystem, as well as the effect that human activities have on a habitat's ability to support life. However, analyzation in this experiment depends on the obtained NPP of fescue plants, which can then be compared to the known value in order to draw more conclusions regarding the environmental factors that impact NPP. For this reason, the problem being addressed in this lab is "What is the NPP of fescue plants," which can be calculated by dividing the biomass of the grass clippings by the area of the opening of the bottle by the amount of days the grass was allowed to grow.
Hypothesis:
If fescue seeds are planted and allowed to grow for six days, then the NPP of the grass will be lower than the known NPP of fescue plants -- 58 g/cm2/year -- because of the limited amount of energy that a lamp can input into the system as compared to natural sunlight.
Parts of the Experiment:
- The control group consists of the known NPP of fescue plants (58 g/cm2/year).
- The experimental group is constituted by each group's plot of fescue plants.
- The independent variable is the light to which the fescue plants are exposed, as well as the water added to the plants (these variables may not exist, but they would be present in a non-observational experiment).
- The dependent variable is the NPP of the fescue plants.
- The controlled variables are the materials, the length to which the fescue plants are cut (2cm), the amount of time the plants are exposed to the light source, and the area of plot for each group's plants.
Materials & Methods:
a) Materials:
- (fescue) grass seeds
- soil
- empty, cut-open two-liter bottle
- paper towels
- metric ruler
- scissors
- petri dish
- digital scales
b) Method:
Lab Day 1:
- Cut all of your grass plants to the same height: Use a ruler to precisely cut all of the blades to a height of 2 cm. Carefully remove and discard all the clippings from your plot. Allow grass to continue to grow for 6 days.
- Cut all of your grass plants to the same height as before: use a ruler to precisely cut all of the blades to a height of 2 cm. Carefully remove all the grass clippings and place them in a petri dish. Allow the clippings to dry for 2 days.
- Measure the area of grass used in your experiment and record in your data table.
- Weigh the grass clippings from lab day 2 and record in your data table. Calculate the net primary productivity using the following formula: NPP=(biomass/area)/day
- Obtain the NPP data from the other groups in your class. Then, calculate a class average for NPP for Fescue.
- The known NPP of fescue plants is found to be 58 g/cm2/year. Compare this average to your average from the lab. Represent the difference using percent error.
Data & Data Analysis:
a) Data:
b) Data Analysis:
When looking at the data collected by the whole class, it seems as though there is a variable absent in this experiment which inhibits any variation in the growth rate, and thus the NPP, of fescue plants. Once the fescue seeds had completed their six-day germination period, and the grass clippings collected were left to dry for two days, the biomass for every group came out to be 0.1 grams. Although many factors could have played a role in the difference between each group's calculated NPP, the area of each plot is the only value that causes discrepancies in the actual calculation. Furthermore, the average NPP of the fescue provided another interesting value for comparison. With an average NPP of 1.0025 X 10^-4 g/cm2/day, the percent error came out to be 99.937%. Perhaps it was the source of light or the soil quality that caused the average NPP from the lab to be remarkably low compared to the known NPP of fescue plants: 58 g/cm2/year. |
|
Conclusions:
The hypothesis stated that if fescue seeds are planted and allowed to grow for six days, then the NPP of the fescue will be lower than 58 g/cm2/year. The results of this experiment proved this hypothesis to be true since the calculated average for fescue came out to be 1.0025 X 10^-4 g/cm2/day, or 3.66 X 10^-2 g/cm2/year. Even after calculating the NPP for a whole year, the percent error remained high. At a surprising 99.937%, this percent error indicates that there are indeed environmental effects on NPP. For example, the fact that the sun was not used as the energy source for the plants, and that students were responsible for watering their plants every other day, could have resulted in a significantly lower NPP. In order for photosynthesis to take place, plants need to capture and store solar energy, collect water, and have a constant source of CO2. Some of these factors influencing plant productivity can simply not be replicated in an indoor setting. In addition, this could be due to left over grass clippings in the soil after cutting the grass, which some groups were not willing or able to collect. Overall, these possible sources of error indicate that this lab was not the best model for testing net primary productivity. NPP is affected by too many environmental factors to be scaled down to such a simple model of complex ecological processes that go on in ecosystems, such as the carbon cycle.
Since any model or experiment for testing net primary productivity is only good in theory, a better way to test an environment effect on NPP would be by manipulating that certain effect. For example, the affect of soil moisture on NPP can be tested by assigning each group a different amount of water to add to their fescue plants on a certain day. Thus, the data at the end of the experiment would reflect this difference in soil moisture. Everything else in the experiment could be kept the same, but the new biomass would be determined by the amount of water added to each fescue. The clippings will then be weighed to determine the biomass, the area of the bottle will be taken and the NPP will be calculated for each group using this formula: NPP=(biomass/area)/day. It is important to understand that NPP is "a measure of the amount of life that can be supported by an ecosystem"(Norris, Kara). Thus, changes in NPP can affect the health of all living things on this planet. One of the main threats is global climate change, for it "tends to lower NPP... and limit the potential of a landscape to [mitigate] climate change through storage of atmospheric carbon dioxide"(Net Primary Production). The threat of global climate change is only exacerbated by the fact that more "carbon dioxide is being released when people burn coal, oil, and other fossil fuels"(NASA). This interaction clearly identifies the importance of NPP as a basis in the sustainability of an ecosystem. Therefore, understanding the primary productivity of an ecosystem should be important to every human being. This information would be important to scientists, especially environmentalist, and environmental organizations (whether aided by the government or not) that advocate ecological balance by sustaining high levels of energy input in an ecosystem.
Citations:
NASA. "Net Primary Productivity : Global Maps." Net Primary Productivity : Global Maps. Earth Observatory, Feb. 2000. Web. 09 Oct. 2014. <http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MOD17A2_M_PSN>.
"Net Primary Production." UC Davis. Information Center for the Environment, n.d. Web. 10 Oct. 2014. <http://ice.ucdavis.edu/waf/model/indicator/net-primary-production>.
Norris, Kara. Net Primary Productivity of Fescue Plants. N.p.: Web. 10 Oct. 2014. PDF.