Download 8-1 THE PREDICTED EFFECTS OF GLOBAL WARMING AND

THE PREDICTED EFFECTS OF GLOBAL WARMING AND CLIMATE CHANGE ON
RYEGRASS
Frank Jiang, Danielle Karacsony, Sophie Lederer, Brian Li,
Rachel Mumma, Roma Patel, Jacklyn Pezzato, Kelsey Schroeder
Advisor: Dr. Arun Srivastava
Assistant: Gillian Bradley
ABSTRACT
As global warming becomes an increasingly salient problem, its effects must be analyzed
from different perspectives. One of the least understood environmental relationships is that
between atmospheric carbon dioxide, temperature, and plant biomass. Plants are a necessary
recycler of carbon dioxide, so if their growth is accelerated due to global warming, they may be
able to remove carbon dioxide from the atmosphere at a faster rate. While studies have initially
concluded that elevated carbon dioxide levels indeed facilitate photosynthesis and thus yield
greater plant growth, most studies agree that significant uncertainty remains. This lies in the role
temperature may play in stunting the terrestrial carbon storage efficiency of soil. As such, a new
experiment in which temperature and carbon dioxide levels were manipulated on ryegrass was
developed. Height of plant growth, carbon-nitrogen soil ratios, and other qualitative
characteristics were recorded. Results showed that higher temperatures yielded better plant
growth, though this might have also been because of variable light settings or water intake.
Carbon dioxide, on the other hand, led to grass with overall greater biomass but less height.
These conclusions have several interpretations, so further research is necessary to refine current
knowledge on this subject. For instance, if all variables but temperature are controlled, its effects
on carbon storage efficiency will be more accurately measured. Other variables, including light
and water, can also be better controlled for more precision. With such future steps, the
relationship between plant biomass and its environment will be clarified and fully understood.
INTRODUCTION
Climate change is a natural periodic process. Ice Ages are followed by warmer
interglacial periods as the Earth alternates between hot and cold cycles. However, recent global
warming has progressed at an unprecedented rate—accelerating so fast, in fact, that many
species have been unable to adapt to the rapid change in conditions (1). As this occurs, entire
ecosystems may be irreparably changed.
While atmospheric carbon dioxide (CO2) has fluctuated throughout geological time, it has
increased recently due to anthropogenic factors, including consumption of fossil fuel and
deforestation. CO2 partial pressure has increased from 27 Pa to 35 Pa since the onset of the
industrial revolution 140 years ago, and is expected to rise to 70 Pa by the end of the century
(23). While the existence of climate change is not a problem in itself, the rate at which the
Earth’s temperature is shifting is. The carbon cycle, a fundamental and natural process, plays a
vital role in this change because it is based on the movement of carbon from inorganic to organic
molecules, manifesting primarily as carbon dioxide in the atmosphere. Carbon dioxide has an
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important property that other major components of air, such as oxygen (O2) and nitrogen (N2), do
not. CO2 is a greenhouse gas and thus absorbs heat. Therefore, as the concentration of
atmospheric CO2 continues to increase, there will be a subsequent increase in temperature around
the world (2).
Estimates have shown that by 2050 there will be an overall increase in global temperature
of approximately 2.8० C, or 5० F (3). While this may appear trivial, the profound impact of
variations in atmospheric conditions is actually the preeminent threat to biodiversity (4). In fact,
studies have shown that all species may not be able to adapt to a changing environment (5). In
addition, previous literature suggests that atmospheric carbon dioxide levels will rise from 400
parts per million (ppm) today to 625 ppm by 2050 (6). This dramatic increase in carbon dioxide
levels will have many adverse effects on the global climate as well as the species that inhabit it.
For instance, plants have already begun to adapt to hotter conditions by utilizing C4
photosynthesis, a process that requires less water and can thrive in harsh conditions (7).
Such adaptations will soon be necessary. As carbon dioxide emissions collect in the
Earth’s atmosphere, a “greenhouse effect” will be created. Trapped heat will cause an increase in
global temperature (8), and much of the ocean will absorb additional carbon dioxide, raising the
acidity and temperature of the water (9) and elevating the sea level from melting ice caps. In
turn, coastal erosion will occur and directly impact nearby inhabitants, who will become more
susceptible to damage from storm waves. Warmer temperatures will also increase the amount of
water vapor in the lower atmosphere, resulting in a more humid environment and unpredictable
weather patterns.
In order to understand global warming, the carbon cycle itself must first be understood.
There are numerous factors in the carbon cycle, including the air-sea gas exchange,
decomposition of organisms, and the carbon stored in the soil, ocean sediments, and fossils (Fig.
1) (10, 11, 12). The two most significant processes in the carbon cycle, however, are
photosynthesis and respiration. During respiration, organisms take in oxygen and release carbon
dioxide. The released carbon is recycled during photosynthesis and returns to its organic state
(13). Plants then use carbon dioxide to create simple glucose and other biological components
according to the following equation:
6CO2 + 6H2O + light → C6H12O6 + 6O2
Fig. 1 The carbon cycle. An
essential natural process that
begins as animals respire and
release CO2. Exploitation of fossil
fuels also releases CO2. Plants
take in the CO2 and exchange it
for O2, though recently the cycle
has destabilized with
deforestation and other
anthropogenic problems.
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The relationship between photosynthesis and carbon is intricate. A greater amount of
carbon dioxide in the atmosphere has been shown to improve plants’ ability to perform
photosynthesis (14). Photosynthesis is the ultimate source of biomass in plants, as the sugars
produced become the organic molecules the plant needs to grow (15). Through photosynthesis,
light energy converts carbon dioxide into the chemical energy contained in carbohydrates and
other biological components (16).
A plant must also take in nutrients from the soil, and therefore the composition of the soil
is very important to plant growth. By determining how much the composition of the soil changed
over time, one may determine how much of what nutrients the plant used during its growth.
Three important nutrients in determining the rate of plant growth include potassium, phosphorus,
and nitrogen. While not directly involved in plant structure, potassium takes an active role in
many biochemical functions, including but not limited to cell division and resistance to disease.
Phosphorus, another vital mineral, plays an important role in energy storage and chemical
transfer within the plant. Finally, nitrogen, in the form of nitrates, is a necessary component for
plant growth. Found in assorted plant structures, adequate levels of nitrogen are needed for
healthy plants and increased yields (17).
However, with increased amounts of carbon dioxide in the atmosphere, the amount of
carbon the earth’s ecosystem takes in could increase. Carbon sequestration might also be limited
by the availability of nitrogen in the soil. Therefore, the carbon-nitrogen ratio of the soil has
important ramifications for the terrestrial ecosystem productivity, atmospheric carbon dioxide
concentration, and the resulting feedbacks on climate as carbon uptake by vegetation exceeds
carbon loss from the soil. Plant nitrogen productivity is defined as how much a plant's growth
depends on the amount of internal nitrogen and as the increase in a plant's dry biomass per unit
time and per unit plant nitrogen content. Efficient use of nitrogen during photosynthesis has been
shown to lead to higher plant productivity (18). Gross plant productivity is equivalent to the
photosynthetic rate, or the CO2 assimilation rate. Nevertheless, net productivity must take plant
respiration into account (19).
There is also an ongoing debate about whether plants, in the forest or grasslands, are
likely to become a net carbon source or sink as a result of increasing temperature, higher
concentrations of atmospheric CO2, or other environmental variables by 2050. These
uncertainties are mainly attributed to the spatial consistency of measured biomass productivity
and how plants’ structure and dynamics change over time. Recent studies by Amazon Forests
Inventory Network (RAINFOR: 20) suggested that the average rate of biomass growth was
stimulated by environmental changes with a significant increase in turnover rates (21). However,
in another study at La Selva, Costa Rica, researchers found that growth rate decreased and
similar trends are reported from Panama and Malaysia (22).
High biomass indicates high glucose production, so calculations can be made regarding
the rate of carbon dioxide uptake to determine how additional carbon dioxide in the atmosphere
will affect plant growth (23). This increase in glucose resulting from an increase in CO2
elongates the carbon cycle by decreasing the amount of carbon dioxide in the atmosphere.
Previous literature by Hughes and Benemann (24) describes observations that conclude that over
ten times more CO2 is fixed by plants into biomass and annually released by decomposers and
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food chains than is emitted by the burning of fossil fuels. With approximately half of the carbon
circulating the Earth because of mankind, gaining the ability to fixate it would be effective in
decreasing the greenhouse gases in the atmosphere.
However, not all of the carbon released is accounted for each year, causing a shift in the
stability of the cycle. With increasing industrialization, humans burn fossil fuels for energy, and
tons of carbon dioxide are released into the atmosphere each year. An increased amount of
carbon dioxide in the air will dissolve more readily into the surface water of the ocean and
become fixed in plants’ biomass. This increase alone results in a facilitation of photosynthesis,
storing more carbon in terrestrial carbon sinks. However, since temperatures will also rise as part
of the climate change process, plant maintenance and soil respiration rates will increase as well,
reducing terrestrial carbon storage efficiency. Because of such uncertainty, it is clear that further
investigation into the relationship between plant biomass and global warming is necessary.
Two different methods exist for measuring the biomass in plants, wet and dry. To
measure the dry biomass of a plant, the water inside the plant must first be evaporated so that
only the organic matter is left. According to Hickman and Pitelka (25), the organic material
represents the energy allocation in the plant, and obtaining the mass of different parts of the plant
distinguishes the tissues in the plant that require the most energy. On the other hand, the wet
weight is a good indicator of both the amount of water the plant contains and the degree of turgor
pressure in the plant. The change from wet weight to dry weight indicates how tolerant of stress
the plant is, with smaller cells being more tolerant of low water potential (26).
As plants are often subjected to periods of soil and atmospheric water shortage, they have
developed complex responses, ranging from drought-avoidance to stress-resistance. Chaves et al.
(27) have studied alterations in nitrogen and carbon metabolism and concluded that they lead to
changes in the root to blade ratio and the temporary accumulation of reserves. In addition, plants
may regulate carbon metabolism through processes other than photosynthesis, an important
defense mechanism in the absence of water.
Biomass measurement is easily possible on a small scale through an invasive method, but
a method that is less destructive for larger scales is greatly preferred. Recent novel methods to
determine biomass on a larger scale have included 3D quadrat, plate meter, and visual estimation
(28). These are methods that can be implemented if this experiment is carried out on a wider
scale.
Beyond just measuring biomass, it is also necessary to determine the carbon-nitrogen
content of soil. As mentioned before, this poses many different ramifications to growth. For
example, carbon sequestration can help growth, but higher temperatures usually signify
respiration and less carbon intake. At the same time, Haney et al. (29) has shown that strong
carbon-nitrogen ratios can lead to more productive and efficient growth. As such, if
environmental conditions can be shown to greatly affect soil conditions, this can lead to new
insights in plant growth.
Höglind et al. (30) have begun such investigations by attempting to model future and
past-based global scenarios. Assorted climate models were tested on two different grass types,
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with the conclusion that there would be a projected increase in grass yield with rising
temperatures in the future. However, the exact impacts of global climate change on the
environment remains unclear.
The purpose of this experiment was thus to analyze the effects of global warming on
plant growth through the study of ryegrass under various conditions. Increased carbon dioxide
levels and raised temperatures were used in order to compare the growth of plants under presentday conditions to that of plants in 2050. If plant photosynthesis is dependent on CO2
concentration, greater CO2 concentration will cause greater plant growth. In addition, if
increased temperature decreases the ability of the plant to take in carbon dioxide by increasing
soil respiration levels, lower temperature will be most beneficial to plant growth. A consensus
could not be reached over whether or not a lower temperature or higher CO2 levels would be
more beneficial to the plant, though the study should establish such conclusions.
MATERIALS AND METHODS
Initial Preparation
Germination of Gulf Annual Ryegrass (Lolium multiflorum Lam.)
In order to begin experimentation, seeds first had to be germinated (Fig. 2). One liter of
Miracle-Gro Organic Choice Garden Soil® was poured into four EZ foil® casserole pans (11 ¾
.mbn, m.mn in. X 9 ¼ in. X 1 ½ in.) each. Six grams of ryegrass seeds were spread evenly across
the surface of the soil before being covered with an additional five hundred mL of soil. Five
hundred mL of water was then added to each tray for moisture.
Fig. 2 Three of the four trays used in growing ryegrass
All four trays were placed in a growth chamber (Fig. 3) for seven days with no light at
32°C. While in the chambers, the trays were rotated from top to bottom for even heat distribution
and watered as needed to keep the soil moist. Variable conditions were not enforced at this stage
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to encourage even germination. Furthermore, as plant biomass is dependent upon photosynthesis,
conditions and light are meaningless until the grass has grown.
Fig. 3 Growth chamber with trays of grass
Fig. 4 Gold connector hold burned into plastic
Preparation of Containers
As the seeds germinated, plastic containers were prepared for future testing. Two of the
plastic containers were modified to allow the injection of CO2. A Bunsen burner was used to heat
one end of a gold connector. Once hot, the connector was pressed into a container and a perfectly
fitted hole was melted into the plastic (Fig. 4). After both of the gold connectors were securely
fitted in their respective holes, the tubing for the carbon dioxide had to be attached. The plastic
tubing inside the container was heated and fused to the gold connector. This process for attaching
the tubes was performed twice per container. It was done once to connect the outside tubing with
the pressurized CO2 gas cylinder and once for the tubing inside the box.
Experimentation
Experimental Setup
After germination occurred, grass growth was observed. In the four trays prepared, there
was a slight variation in the density of the grass - the two trays with lower carbon dioxide levels,
regardless of temperature, grew denser than the others.
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Fig. 5 Recombined tray of grass from two trays
To compensate for this variation, each tray was cut in half. Then the trays with sparse
growth were paired with trays situated in low carbon dioxide levels (Fig. 5). This allowed for an
equal distribution of grass. To ensure accurate simulations of the four different environments
(Fig. 6), each plastic container was covered and taped shut. The high CO2 plots were pumped to
625 ppm with a carbon dioxide tank. The high temperature plots were placed in a growth
chamber. The low temperature and low carbon dioxide conditions were both set to room levels.
To further model each environment, 50 mL of water were added inside the plastic container to
create a moderate level of humidity for the grass in the aluminum tray. A thermometer was
placed in each container to monitor temperature (Fig. 7).
Fig. 6 Chart of four different environments and their respective conditions
Conditions
Low Temperature (room)
High Temperature (29°C)
Low CO2 (room)
Tray 1- Present Conditions
Tray 2
High CO2 (625 ppm)
Tray 3
Tray 4- 2050 Conditions
Fig. 7 Final set-up of container with water and thermometer
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Data Collection
Data, such as height and other salient qualitative observations, were collected every other
day. To calculate the average height of each tray, ten random blades of grass were measured. On
the seventh day in the controlled environment, grass samples were taken to determine the
biomass and soil content. Biomass was measured for both aboveground and belowground,
providing an overall biomass. This process was begun by removing a 5.5 x 6.25 cm plot of grass
and soil from each of the four conditions represented. Excess soil was as gently removed from
the plot of grass as possible by hand. To ensure that most of the soil was being removed, the
grass was washed and then lightly dried with cool air so that the water inside the grass did not
evaporate. This process allowed for maximum soil removal (Fig. 8).
Fig. 8 Separation of grass from the high CO2, low-temperature environment and soil by hand
Since the roots and the blades of the grass needed to be measured for biomass separately,
each shoot of grass was cut directly at the soil line. The wet mass of each component was taken.
The roots and blades were then placed in an oven for one hour to allow for the evaporation of
water from the grass before the mass was taken again, this time yielding the dry biomass.
The soil that had been removed from each plot was tested for phosphorus, nitrate, pH,
and potassium, using a Soil Test Kit by Luster Leaf Products, Inc. To test for phosphorus, a
solution of soil and phosphorus extractant, containing molybdate, was created to form a
phosphor-molybdate compound. A reducing agent which included stannous chloride was added
as an indicator of the amount of phosphorus present in the soil. Nitrogen, in the form of nitrate,
was tested for by utilizing cadmium, a component of a nitrate-reducing agent that produces a red
dye through a diazotization reaction, meant to indicate the amount of nitrate present in the soil.
Barium sulfate and a pH testing solution created a mixture for determining the acidity of the soil.
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In testing for potassium, the soil was made alkaline, and the potassium reacted with a sodium
tetra phenyl boron solution to form a precipitate. The resulting cloudiness of the solution
indicated how much potassium was present in the soil (Fig. 9).
Fig. 9 Different soil tests (pH, phosphorus, nitrate, and potassium from top left to bottom right)
with charts for concentration analysis
In addition, the carbon-nitrogen ratio was tested using the Solvita gel system. Clumps and
wood chips were removed from the soil, and containers were filled up approximately halfway
with soil. The soil was then allowed to stand for one hour before the carbon dioxide and
ammonia probes were placed inside and the caps screwed on for four hours. The color of the
strips at the end of the four hours indicated the respective concentrations (Fig. 10).
Fig. 10 Carbon dioxide and ammonia probes, along with CO2 chart for color analysis
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RESULTS
Qualitative observations of grass color and relative density were made every time the
height of the grass was measured. Both of the high temperature plots were very green throughout
the experiment. The low CO2 plot was the densest of all the plots, and the high CO2 plot was the
least dense. The low temperature plots were yellow-green and maintained medium densities, but
the high CO2 plot was slightly denser than the low CO2.
Fig. 11 Height of grass over time
20
Height (cm)
18
16
Low Temp./Low CO2
Low Temp./High CO2
14
High Temp./Low CO2
High Temp./High CO2
12
10
8
2 Days
5 Days
7 Days
The heights of the grass in the low CO2 plots grew much taller than the grass in the high
CO2 plots (Fig. 11). In general, they exhibited increased height and growth rates compared to the
high CO2 plots, though there may be some sampling error due to the fact that only ten randomly
selected blades of grass were selected. The high temperature, low CO2 grass was much taller
than its high CO2 counterpart, indicating that the level of CO2 in the environment does have an
effect on the length of the grass blades. Separate analysis of the low temperature grass heights
leads to the same conclusion.
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Fig. 12 Wet biomass of grasses
4.5
4
3.5
Mass (g)
3
Low Temp./Low CO2
2.5
Low Temp./High CO2
2
High Temp./Low CO2
1.5
High Temp./High CO2
1
0.5
0
Total
Blades
Roots
The wet biomasses of the samples in each set of conditions shows that most of the wet
biomass resides in the blades (the above-ground portion of the grass), instead of in the roots (Fig.
12). The wet biomasses of the two low temperature plots show very similar results regarding wet
biomass. However, the high temperature plots contrast each other in a way that allows
conclusions to be drawn about the effect of CO2 on biomass. The high temperature, low CO2 plot
had the greatest wet biomass by far. In fact, its total wet biomass almost doubled that of each of
the other samples. The high temperature low CO2 plot appears to have grown the best overall
when looking at the heights and the wet biomass. The opposite is true for the high temperature,
high CO2 plot. However, this dramatically changes when the dry biomass is taken into account.
Fig. 13 Dry biomass of grasses
0.8
0.7
Mass (g)
0.6
Low Temp/Low CO2
0.5
Low Temp./High CO2
0.4
High Temp./Low CO2
0.3
High Temp./High CO2
0.2
0.1
0
Total
Blades
Roots
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The dry biomass is effectively a measurement of the total tissue in the plant. The dry
biomass data (Fig. 13) is an extremely dramatic change from the wet biomass data. First of all,
the majority of the mass seems to reside in the roots when the dry biomass is taken instead of in
the blades like when the wet biomass was taken. This indicates that most of the grass’s water
weight resides in the blades and that most of the grass’s tissue is contained in the roots. Also, the
high temperature, high CO2 sample went from having the most wet biomass to having the least
when the water was removed. Conversely, the high temperature, high CO2 sample had the
greatest dry biomass by far even though it had the lowest wet biomass. Therefore, this data
suggests that high CO2 levels have a significant effect on the dry biomass of the grass in that
high CO2 levels lead to an increase in plant tissue.
Fig. 14 Percentage of water in biomass
100
90
80
% Water
70
60
50
40
30
20
10
0
Low Temp./Low CO2 Low Temp./High CO2 High Temp./Low CO2 High Temp./High CO2
Conditions
It is evident that high temperature and high CO2 has the lowest percentage of water by
biomass (Fig. 14) and that high temperature and low CO2 has the highest percentage. This
explains why there was such a drastic change from the wet biomass graph to the dry biomass
graph. The two low temperature plots had very similar percentages of water, which explains why
both their dry and wet biomasses do not differ from each other much.
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Fig. 15 Soil testing results
1 - low CO2, low
temp
2 - low CO2,
high temp
3 - high CO2,
low temp
4 - high CO2,
high temp
Initial Testing
pH
Potassium
Nitrate
Phosphorus
CO2
Ammonia
Slightly acidic
High-medium
Medium
High-medium
8 (minimal)
5 (minimal)
Slightly acidic
High-medium
Medium
High-medium
8
5
Slightly acidic
High-medium
Medium
High-medium
8
5
Slightly acidic
High-medium
Medium
High-medium
8
5
Test Day 2
pH
Potassium
Nitrate
Phosphorus
slightly acidic
high-medium
low
high-medium
neutral
high-medium
medium-low
high-medium
slightly acidic
high-medium
low
high-medium
slightly acidic
medium-low
low
high-medium
Test Day 3 (Final
Day)
pH
Potassium
Nitrate
Phosphorus
CO2
Ammonia
neutral
medium
low
high-medium
8
5
neutral
medium
low
high-medium
8
5
neutral
medium
low
high-medium
7.5 (a bit more)
5
neutral
medium-low
low
high-medium
7.5 (a bit more)
5
After the two days of soil testing (Fig. 15), results were compiled and compared.
Significant changes occurred in pH, potassium level, carbon dioxide level, and amount of
nitrates, though the pH change may be attributable to carbon’s buffering effect. After the first
testing day, three of the four trays proved to be slightly acidic, but after two more days of
growth, all four trays changed back to neutral. In addition, three of the four trays decreased in
potassium levels from medium-high to medium. The amount of nitrates also decreased, most
likely suggesting that it was used up as the grass grew (nitrogen and potassium are essential for
plant growth). Furthermore, while ammonia levels remained constant, the high CO2 plots wound
up increasing slightly in soil carbon content, suggesting that the carbon wound up being
sequestered as expected.
CONCLUSION
Initially, the grass that grew in the low carbon dioxide and high temperature environment
was observed to be sublime in terms of both height and color after two days of exposure.
However, after the dry biomass was calculated, it became apparent that the grass in this
environment had one of the least total biomasses. As a result of the significant difference
between the dry and wet biomasses, the grass growing in the low temperature and high carbon
dioxide conditions was the least stress-tolerant of the grasses in terms of water potential.
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The initial hypothesis was both supported and refuted. The “green” growth, or the growth
of the blade, was the highest when the CO2 levels were low. However, the total biomass was the
greatest in conditions with high CO2 levels. Most of the carbon dioxide must have gone to the
soil and roots since the blade growth in conditions with high CO2 levels was not apparent. With
greater amounts of carbon dioxide in the roots, a more intricate support system grew. In turn, this
root system would provide long term annual stability to prevent the grass from dying. Pineapple,
cacti, and other plants growing in high temperatures undergo similar stress-resistant techniques
to survive in harsh climates using C4 photosynthesis.
While high amounts of CO2 did not lead to ideal grass in terms height, density, or
appearance as expected, it did lead to an overall increase in dry biomass when temperature was
held constant. However, the reason why the grass blades’ mass decreased in high carbon dioxide
environments remains unknown. In order to further understand this topic, the experiment must be
modified to account for specific variables since the current experiment did not present
justification.
During soil testing, there were several salient factors which changed significantly. The
pH levels went from slightly acidic to neutral in all conditions, though this might have been
because of carbon’s buffering effect as it was gradually sequestered over time. Furthermore, both
potassium and nitrate levels decreased as the two were likely used for plant growth. Thus, these
changes in soil content were relatively expected but still helped to yield insights as to plant
development.
On a wider scale, an increase in CO2 in the atmosphere would lead to fewer plants with a
high amount of wet biomass in blades of grass. Since these blades are responsible for
photosynthesis, the amount of oxygen released from plants into the atmosphere would
significantly decrease. Furthermore, since root biomass increased in the high CO2 and high
temperature environment and roots undergo respiration, the above implications are further
emphasized. These factors, combined with deforestation, could quickly worsen in a vicious circle
of climate change, making the reparation process much harder.
Limitations
Although we attempted to design a controlled and accurate experiment, several possible
sources of error may have affected our results. After germination, the “high temperature”
samples were grown in a growth chamber, while the “low temperature” samples were grown in
an isolated room. The light in the growth chamber was more powerful than the light in the
isolated room, and within the growth chamber, the top shelf and bottom shelf experienced
different light intensities. Measured at 500 nm, the light in the isolated room was 172 nW, the
light on the top shelf of the growth chamber was 305 nW, and the light on the bottom shelf of the
growth chamber measured 218 nW. For this reason, the “high temperature, low CO2” sample
was exposed to considerably more light than the other samples, potentially explaining why this
sample was the most dense and green. Additionally, the white walls of the growth chamber may
have reflected more light than the darker beige walls of the isolated room, exposing the “high
temperature” samples to more intense light and thus extra room for growth.
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Our first measurement involved the height of the grass in each tray. So as to avoid too
invasive a procedure, we chose to measure the height of six random blades in each sample.
Although this method did allow the grass to grow regularly without any change, it also may have
affected our results. It is possible that taller-than-average grass blades were selected in one
sample while shorter-than-average blades were measured in another. Because of this sampling
error, the height of a particular sample may have been misrepresented by the data collected.
However, this likely is not very significant.
Our second measurement, biomass, presented possible sources of error as well. When
extracting a sample to measure, we used a constant area, but the volume of our sample may have
differed as the depth of each tray varied slightly. This would result in a slightly inaccurate
comparison of the biomasses of each sample. A random patch of grass for each biomass
measurement was chosen as well, and it is possible that the selected patch for each tray was not
the best representation of ryegrass growth in that sample. Furthermore, when separating the roots
from the blades, some contamination or accidental mixing may have occurred and skewed the
results. This could have led to an uneven ratio between the root and blade mass. Some soil also
may have been included in our biomass measurements since the grass is hard to completely clean
and separate.
Future Direction
For future experiments, the effect of different lighting on plant growth could be tested to
ensure greater precision. Another variable that could be investigated further is the amount of
water given to each plot of grass. The grass in this experiment was watered as needed to maintain
a relatively consistent moisture level. This ensured that water would not limit the growth of the
grass nor add another variable to the experiment. For instance, the higher temperature plots
might have been given more water over the course of the experiment and allowed them to grow
at a faster rate. Therefore, a future experiment could add water and lighting as additional
variables alongside temperature and CO2.
ACKNOWLEDGEMENTS
The authors of this study would first and foremost like to thank Dr. Srivastava for his
patient suggestions, wise thoughts, and detailed explanations. We simply could not have had a
better mentor. We would also like to thank Gillian Bradley for her unending kindness and helpful
comments. Further thanks go to Dr. Miyamoto and the Governor’s School in the Sciences staff
for putting together such an amazing experience. And last but definitely not least, our thanks go
to the Governor’s School Scholars themselves, for without them we could not have met such an
incredible group of inspiring people.
REFERENCES
1. [US EPA] United States Environmental Protection Agency. 2012 June 14. Climate Change
Basics. <http://www.epa.gov/climatechange/basics/>. Accessed 2012 July 30.
2. Cox, P. M., Betts, R., Jones, C. D., Spall, S., & Totterdell, I. J. (2000). Acceleration of
8-15
global warming due to carbon-cycle feedbacks in a coupled climate model. Nature,
408(6809), 184-7. doi:10.1038/35041539
3. Davis, S. J., Caldeira, K., & Matthews, H. D. (2010). Future CO2 emissions and climate
change from existing energy infrastructure. Science (New York, N.Y.), 329(5997), 1330-3.
doi:10.1126/science.1188566
4. Malcolm, J. R., Liu, C., Neilson, R. P., Hansen, L., & Hannah, L. (2006). Global Warming
and Extinctions of Endemic Species from Biodiversity Hotspots. Conservation Biology,
20(2), 538-548. doi:10.1111/j.1523-1739.2006.00364.x
5. Berteaux, D., Réale, D., McAdam, A. G., & Boutin, S. (2004). Keeping pace with fast climate
change: can arctic life count on evolution? Integrative and comparative biology, 44(2),
140-51. doi:10.1093/icb/44.2.140
6. Hawksworth, J. (2006). The World in 2050: Implications of global growth for carbon
emissions and climate change policy, (September), 1-67.
7. Osborne CP, Sack L. Evolution of C4 plants: a new hypothesis for an interaction of CO2 and
water relations mediated by plant hydraulics. Philosophical transactions of the Royal
Society of London. Series B, Biological sciences [Internet]. 2012 February
19;367(1588):583–600. Available from: http://www.ncbi.nlm.nih.gov/pubmed/22232769
7. Ramanathan, V. (2011). Resolution of Outstanding Issues in Climate Research with Earth
Radiation Budget Data: Past and Future. Clouds and the Earth’s Radiant Energy System
(CERES) Science Team Meeting.
8. Raven, J. (2005). Ocean acidification due to increasing. The Royal Society, (June). Retrieved
from www.scar.org/articles/Ocean_Acidification(1).pdf
9. Ophardt, C. E. (2003, April). Carbon Dioxide and Fossil Fuels. Virtual Chembook. Retrieved
July 26, 2012, from http://www.elmhurst.edu/~chm/vchembook/globalwarmA4.html
10. Riebeek, H. (2011). The Carbon Cycle. Nasa. Retrieved July 27, 2012, from
http://earthobservatory.nasa.gov/Features/CarbonCycle/
11. [NCAR] National Center for Atmospheric Research. 2012. Cycles of the Earth System.
Living in the Greenhouse! <http://www.eo.ucar.edu/kids/green/cycles1.htm>. Accessed
2012 July 30.
12. Held, I. & Soden, B. (2006). Robust responses of the hydrological cycle to global warming.
Journal of Climate. Retrieved from
http://journals.ametsoc.org/doi/pdf/10.1175/JCLI3990.1
13. Beadle, C. L., & Long, S. P. (1985). Photosynthesis — is it limiting to biomass production?
Biomass, 8(2), 119-168. doi:10.1016/0144-4565(85)90022-8
14. Herrick, J. D., & Thomas, R. B. (1999). Effects of CO2 enrichment on the photosynthetic
light response of sun and shade leaves of canopy sweetgum trees (Liquidambar
styraciflua) in a forest ecosystem. Tree Physiology, (Bowes 1993), 779-786. Retrieved
from http://treephys.oxfordjournals.org/content/19/12/779.short
15. Barber, J. (2009). Photosynthetic energy conversion: natural and artificial. Chemical Society
reviews, 38(1), 185-96. doi:10.1039/b802262n
16. Vertregt, N. (1987). A rapid method for determining the efficiency of biosynthesis of plant
biomass. Journal of Theoretical Biology, 109-119. Retrieved from
http://www.sciencedirect.com/science/article/pii/S0022519387800346
17. Wheet R. Soil Chemistry Laboratory Manual Introduction to Agriculture Chemistry.
Retrieved from
http://chemtech.org/cn/scit1305/Soil%20Test%20Laboratory%20Manual.pdf
8-16
18. Garnier, E., Gobin, O., & Poorter, H. (1995). Nitrogen Productivity Depends on
Photosynthetic Nitrogen Use Efficiency and on Nitrogen Allocation Within the Plant.
Annals of Botany, 76, 667–672. Retrieved from
http://aob.oxfordjournals.org/content/76/6/667.full.pdf
19. Lloyd, J. (1999). The CO 2 dependence of photosynthesis , plant growth responses to
elevated CO 2 concentrations and their interaction with soil nutrient status , II .
Temperate and boreal forest productivity and the combined effects of increasing CO2
concentrations and i. Functional Ecology, 13(4), 439–459. Retrieved from
http://onlinelibrary.wiley.com/store/10.1046/j.1365-2435.1999.00350.x
20. Malhi, Y. et al. (2002). An international network to monitor the structure, composition and
dynamics of Amazonian forests (RAINFOR). J. Veg. Sci. 113, 439-450.
(doi:10.1111/j.1654-1103.2002.tb02068.x)
21. Phillips, O.L. et al. (2004). Pattern and process in Amazon tree turnover 1976-2001. Phil.
Trans. R. Soc. Lond. B 359, 381-407. (doi:10.1098/rstb.2003.1438)
22. Feeley, K. J. et al (2007). Decelerating growth in tropical forest trees. Ecology 10, 461-469.
(doi:10.1111/j.1461-0248.2007.01033.x)
23. Hughes, E., & Benemann, J. R. (1997). Biological fossil CO2 mitigation. Energy Conversion
and Management, 38, S467–S473. doi:10.1016/S0196-8904(96)00312-3
24. Primack, R. B. (2002). The Carbon Cycle & The Greenhouse Effect. Essentials of
Conservation Biology (Third., Vol. 8, pp. 239-248). Boston: Sinauer Associates, Inc.
Retrieved from http://www.snre.umich.edu/~dallan/nre220/outline20.htm
25. 1. Pitelka J, Hickman C, Louis F. International Association for Ecology Dry Weight
Indicates Energy Allocation in Ecological Strategy Analysis of Plants. Springer in
cooperation with International Association for Ecology. 2012;21(2):117–121.
26. Cutler JM, Rains DW, Loomis RS, Science R. The Importance of Cell Size in the Water
Relations of Plants. 1977;(Levitt 1972):255–260.
27. Chaves MM. How Plants Cope with Water Stress in the Field? Photosynthesis and Growth.
Annals of Botany [Internet]. 2002 June 15 [cited 2012 July 17];89(7):907–916. Available
from: http://aob.oupjournals.org/cgi/doi/10.1093/aob/mcf105
28. Redjadj C, Duparc a., Lavorel S, Grigulis K, Bonenfant C, Maillard D, Saïd S, Loison a.
Estimating herbaceous plant biomass in mountain grasslands: a comparative study using
three different methods. Alpine Botany [Internet]. 2012 February 10 [cited 2012 August
2];122(1):57–63. Available from: http://www.springerlink.com/index/10.1007/s00035012-0100-5
29. Haney RL, Brinton WH, Evans E. Estimating Soil Carbon, Nitrogen, and Phosphorus
Mineralization from Short Term Carbon Dioxide Respiration. Communications in Soil
Science and Plant Analysis [Internet]. 2008 October [cited 2012 July 23];39(1718):2706–2720. Available from:
http://www.tandfonline.com/doi/abs/10.1080/00103620802358862
30. Höglind, M., Thorsen, S. M., & Semenov, M. A. (2012). Assessing uncertainties in impact of
climate change on grass production in Northern Europe using ensembles of global
climate models. Agricultural and Forest Meteorology.
doi:10.1016/j.agrformet.2012.02.010
30. Peneuelas, J., Canadell, J. C. and Ogaya, R (2011). Increased water-use efficiency during the
20th century did not translate into enhanced tree growth. Global Ecology and
Biogeography, 20: 597.608.
8-17