Kelsey Salter conducted a study to determine how fossil fuel exposure from a construction site affects the foliar nitrogen level in Colorado Blue Spruces. She hypothesized that the tree exposed to fossil fuels (Tree 1) would have a higher carbon-to-nitrogen ratio than an unexposed tree (Tree 2). However, her results showed that Tree 2, located near a parking lot, had a higher ratio. While the ranges were small, vehicle exhaust may explain Tree 2's poorer health despite its location in the arboretum. Further study is needed as many factors influence foliar nitrogen.

1. Kelsey Salter
Class Project
Spring 2017, FOR 221, Ecology
Scientific Question:
How does fossil fuel exposure at a construction site affect the foliar nitrogen level in a Colorado
Blue Spruce versus a Colorado Blue Spruce at a site without a fossil fuel source?
Hypothesis: CO2, Nitrogen and nitrous oxide released by the burning of fossil fuels work during
the construction site at the Integrated Research and Learning Center will cause the Colorado
Blue Spruce to have less foliar nitrogen content than a tree of the same type that is not exposed
to a construction site. The carbon to nitrogen ratio for trees exposed to fossil fuels will be higher
than the carbon to nitrogen ration for unafflicted trees.
Rationale: I base this hypothesis on the fact that previous studies suggest that plant forms that
are exposed to higher concentrations of CO2 have been shown to have a decreased foliar
nitrogen content because in reaction to increased CO2, plants began taking up less H2O. Plant
ecosystems that have been exposed to the burning of fossil fuels have also been noted to have
been subjected to disruption in the nitrogen cycle. In this case, elevation factors into my
hypothesis because according on the University of Idaho campus the higher the elevation, the
healthier the environment is for the tree. As the elevation climbs, the campus opens to the
arboretum and botanical garden, which is farther away from the burning of fossil fuels.
Methods
Study site: I investigated the impacts that a construction site on the campus of University of
Idaho has on plant life nearby. The Integrated Research & Learning Center (IRIC) broke ground
in 2014 and was completed in late 2016. During this period, plant life nearby was exposed to
fossil fuels such as carbon dioxide, nitrous oxide, and nitrogen. My first specimen of focus was a
large Colorado Blue Spruce (Picea pungens) located between the IRIC and Bring & Phinney

2. halls. This subject is labeled TREE 1. I was unable to determine the exact age of TREE 1, but
Google Earth images indicates that TREE 1 was exposed to the construction site of the IRIC
from 2014 to 2016. (See Fig.1). The elevation of TREE 1 was 2450 feet.
The second study site was
another Colorado Blue Spruce
next to the University of Idaho
tennis courts, across campus
from Tree 1. This tree was
labeled TREE 2. (See Fig. 2)
TREE 2 had a noticeable height
deficit compared to Tree 1 and I
hypothesized this tree is
therefore younger in age. The
mean annual temperature in
Moscow, Idaho is 8.75℃. The
mean annual precipitation is 688
mm. These trees have been
exposed to a great deal of
precipitation over the course of one year and largely
have existed in a cold environment. The elevation of
Tree 2 is 2480 feet, 30 feet higher than TREE 1.
Approach: For sampling TREE 1, I used a large pair of scissors to cut approximately 6 cm from
the end of a branch at three different points from the bottom level of the tree and placed each
sample in sealed plastic bags. Each sample was subsequently labeled KS1, KS2, and KS3.
Utilizing the same process, I cut 6 cm of material off the end of three different branches from
TREE 2. This time, I elected to collect from the middle position on the tree, approximately 1.219
m in height. Each sample was then placed in sealed plastic bags and labeled KS4, KS5, and KS6.
After placement in a freezer overnight, I sloughed the needles off the branches and the samples
Figure 1. Tree 1 a Colorado Blue Spruce (Picea pungens), circled in red next to an
aerial image photographed by Google Earth during reconstruction in 2015.
Figure 2: Tree 2, a Colorado Blue Spruce (Picea
pungens), is circled in red on this aerial photograph
captured by Google Earth in 2015. Tree 2 is situated
next to the University of Idaho Tennis Courts.

3. were sent in for laboratory testing to determine the carbon-to-nitrogen ratio. All samples were
collected on March 22, 2017. The mathematical calculations used to determine the ratio is the
proportion of nitrogen in the needle and the proportion of carbon in the needle. This makes up the
carbon-to-nitrogen ratio.
Results
I found that the samples from the unaffected tree (TREE 2) contained a higher carbon-to-nitrogen
ratio than the samples from TREE 1. According to Table 1, KS1 had a CN of 36.3, KS2 had a CN
ratio of 36.6. KS3had a CN ratio of 37.1. These first three samples all belonged to the tree exposed
to burning fossil fuels. The samples from the unaffected tree (TREE 2) contained higher carbon-
to-nitrogen ratios. KS4 had the highest CN ratio of 42.0. KS5 had a ratio of 39.0, and KS6 had a
ratio of 37.3. These results demonstrated that the higher the CN ratio, the higher the elevation of
the tree.
Sample ID Location Species Canopy
Position
Elevation
(ft.)
Location
on
Branch
%C %N CN
KS1 46.728489, -
117.012544
Picea
pungens
Bottom 2450 End 49.81 1.4 36.3
KS2 46.728489, -
117.012544
Picea
pungens
Bottom 2450 End 49.38 1.4 36.6
KS3 46.728489, -
117.012544
Picea
pungens
Bottom 2450 End 49.65 1.3 37.1
KS4 46.725466, -
117.014422
Picea
pungens
Middle 2480 End 49.68 1.2 42.0
KS5 46.725466, -
117.014422
Picea
pungens
Middle 2480 End 49.75 1.3 39.0
KS6 46.725466, -
117.014422
Picea
pungens
Middle 2480 End 49.36 1.3 37.3
Table 1 Samples along with their coordinates, canopy positions, elevation, and branch location s reflected
against their percent foliar carbon, percent foliar nitrogen, and carbon-to-nitrogen ratio.

4. Chart 1 The carbon-to-nitrogen ration reflected against the elevation of the sample. The trendline shows an increase
in elevation along with an increase in CN ratio.
Discussion and Conclusion
In contrast to my initial hypothesis, a tree that is exposed to the burning of fossil fuels from a
construction site (TREE 1) has a lesser carbon-to-nitrogen ratio compared to a tree that is closer
to the natural environment of University of Idaho arboretum and not near the construction site
(TREE 2). These results do not support my hypothesis; however, I have found possible reasoning
for this outcome. TREE 2 is also located next to a parking lot that services the University
swimming center. It is possible the CN ratio is higher in TREE 2 samples because of the constant
and long-term exposure to the car exhaust at the parking lot. Because of these conditions, I can
hypothesize that the health of TREE 2 is worse than the health of TREE 1 regardless of its location
near the arboretum. However, the range of the ratios were not very significant, and there are many
other factors that may contribute to this such as soil moisture, temperature and precipitation.
References
Roberts, Tara. "The Future Is Wide Open." Here We Have Idaho 2016: n. pag. Web.
<https://www.uidaho.edu/news/here-we-have-idaho-magazine/past-issues/2016-fall/iric>.
"Temperature - Precipitation - Sunshine - Snowfall." Climate. U.S. ClimateData, n.d. Web. 29
Apr. 2017. http://www.usclimatedata.com/climate/moscow/idaho/united-states/usid0170/2017/1
How Does Burning Fossil Fuels Affect the Nitrogen Cycle?" Sciencing. N.p., n.d. Web. 29 Apr.
2017. http://sciencing.com/burning-fuels-affect-nitrogen-cycle-5117705.html>
KS1 KS2 KS3
KS4KS5KS6
2445
2450
2455
2460
2465
2470
2475
2480
2485
2490
36 37 38 39 40 41 42 43
Elevation
CN Ratio
CN Ratio and Elevation

5. Stitt, M., and A. Krapp. "The Interaction between Elevated Carbon Dioxide and Nitrogen
Nutrition: The Physiological and Molecular Background." Plant, Cell and Environment22.6
(1999): 583-621. Web
Harrison, Ph.D. John Arthur. "Visionlearning.com." Visionlearning. Visionlearning, Inc., 11 Feb.
2017. Web. 29 Apr. 2017. <http://www.visionlearning.com/en/library/Earth-Science/6/The-
Nitrogen-Cycle/98>.
Images from Google Earth