NPP Lab

Collaborators: Alex King ,Micaela Strickland, Habiba Fofana.

Introduction:

Primary productivity is the measured amount of photosynthesis that an ecosystem undergoes. GPP or Gross primary productivity is the total amount of primary productivity. The NPP of an ecosystem is important because it can help to indicate the health of that ecosystem. Ecosystems with high NPP promote biodiveristy and can support many animals. Many animals depend on grass for food and other animals higher in the food chain depend on those animals for food, in this lab we will answer the question "What is the net primary productivity of (fescue) grass?"

 

Problem: What is the NPP of fescue plants?

 

Hypothesis: 
If the NPP of the plot of grass is calculated, then it will be lower than an NPP of 58g/cm^2/year.

 

Parts of the Experiment: 

• Independent Variable: the height at which the grass is cut

• Dependent Variable: the growth of the grass in the given amount of time

• Controlled Variables: the materials, amount of sunlight, temperature

• Experimental Group: the plots of grass

 

Materials: 

• Grass seeds

• Soil

• Plastic two liter bottle (empty)

• Ruler

• Scissors

• Scale

• Paper Towels

 

Method: 
1) Fill the empty two liter bottle with soil.
2) Spread a handful of grass seeds into the soil, making sure they are spread evenly.
3) Use a wet paper towel to keep the seeds moist.
4) Let the grass grow until it looks healthy and tall. Cut the grass to 2 cm after some time.
5) After 12 days pass, cut the grass to a height of 2cm once more. Collect the grass that you cut.
6)  Give the grass 2 days to dry out before you weigh it.
7) Weigh the grass using a digital scale and record how much you weighed.
8) Measure the area of grass that you planted in the 2 liter bottle.
9) Record the data in the table. Then calculate the NPP of your grass.
10) Collect the data from your other classmates and figure the average NPP of the entire class.
11) Compare your data with the class average. Use this to calculate the percent error.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

My group's NPP was higher than the average NPP for the class, and the percent error was 99.4 percent. This high percent error can be explained by human error in the experiment.   One, it could been because there was inaccurate measurements causing the height of the grass to be cut incorrectly. Two, the school water that we were watering the grass with could have been less nutritious than actual rain water. Three, it could have been the creation of an artificial enviornment that caused the NPP to be lower. Four, the grass might have been too densely packed, or maybe it wasn't packed densely enough.
    The class's average NPP is  lower than the known average NPP for fescue plants. It was noticeable that some groups had more grass growing in their two liter than others. 

 

Conclusion:

1. Average NPP per day: 9.451x10^-5 g/cm^2/day
Average NPP per year: .0272 g/cm^2/year
2. Group percent error (based on class average): 57.2 percent

3. This was not a good model for testing NPP. This is due to the great amount of human interaction that the grass had in the experiment, as opposed to the very little interaction grass usually has in nature

4.In an experiment to test an environmental effect on NPP, we could set up three different plots of grass. One plot would be watered with regular water, the other plot with acid rain and the other plot with salt water. The lab would follow the same method at this lab, and it would measure the best water to water grass with that would yeild the highest NPP.

5.The NPP of an ecosystem is great way to measure how healthy an ecosystem is. This information would be important to ecologist to see how well energy is flowing through an ecosystem

 

My original hypothesis was incorrect, the NPP was higher than 58g/cm^2/year. The great difference in NPP resulted mostly from human erros and because this was the classes first time doing this experiment. The class had no set method of doing the experiment. Different amounts of water were giving to each set of grass and most likely different anounts of sunlight. This probably skewed data. Also, no data was available from classes from other years to compare the data to in order to evaluate whether this was done correctly. Based on the data, the experiment seems like an inefficent way to calculate NPP. According to Bio Classes.edu variation of NPP is an important indictator of ecosystem health and is the ultimate source of energy for all organisms in an ecosystem 

 

Citation

.., and Ener. Ecosystem Ecology —energy and (n.d.): n. pag. Web.