Houseplant carbon-dioxide sequestration in a semi-enclosed interior
Landon M. Moores
Department of Conservation Social Science, University of Idaho McCall Field
Campus, McCall ID 83638
Summary
1.The carbon-dioxide concentration in a small semi-enclosed interior space was
tested with and without the presence of three common houseplants.
2. Measurements were collected over a 24-hour period, for a total of five datasets
from 2 different days and one control.
3. Datasets were not sufficiently robust for statistical analysis; therefore, graphical
analysis was applied.
4. Other studies support plants as slight carbon sinks.
Synthesis: Study was inconclusive. This research, coupled with current ongoing
parallel studies, serves as a model for future studies that would take carbon dioxide
measurements, light availability, soil moisture, and growing season into account.
Key words: carbon sink, carbon-dioxide flux, carbon-dioxide sequestration,
photosynthesis, respiration,
Introduction
Anthropogenic activity has greatly changed the global carbon cycle,
evidenced by a rise in carbon dioxide (CO2) and other greenhouse gas (GHG)
emissions (IPCC, 2008). This rise in CO2 and other GHGs alters atmospheric carbon
flux in the terrestrial biosphere (Coursolle et al., 2006; Battle et al., 2000; Bousquet
et al., 2000). Because plant growth, temperature, and CO2are inextricably linked
(Morton, 2008; Leakey et al., 2009), as atmospheric CO2 increases, plants react
through increased photosynthesis and decreased stomatal conductance (Morton,
2008; Leakey et al., 2009; Ainsworth & Rogers, 2007). Increased photosynthesis
results in carbon dioxide being removed from the atmosphere and deposited into
the soil (Morton, 2008). Increased temperatures caused by global warming would
increase soil organic matter decomposition changing soils from carbon dioxide sinks
into carbon sources (Janssens et al., 2001; Morton, 2008). Furthermore, in the past
20 years, annual CO2 in the atmosphere has vacillated between one and six gigatons
per year (Bousquet et al., 2000). Since the emission of CO2 into the atmosphere
through fossil fuels remains fairly unchanged, this fluctuation can be attributed to
oceanic and terrestrial fluctuations (Bousquet et al., 2000). The earth’s carbon cycle
is made up of a biological and geological component. Approximately 16.7% of
atmospheric CO2 is fixed annually through photosynthesis (Morton, 2008). The
annual CO2 flux from terrestrial biospheres is more than ten times greater than that
of fossil fuel emissions (Coursolle et al., 2006). In order to understand the earth’s
carbon uptake potential, the carbon sink potential of terrestrial ecosystems must
first be better understood (Coursolle et al., 2006, Battle et al., 2000). Currently there
are over four hundred research sites on six continents recording CO2 fluctuations.
This prevalence of research further evidences the importance of CO2 monitoring.
In a recent IKEA advertisement, a selection of houseplants is highlighted with
the following text, “Fill the bathroom with plants. They add color, shape and texture
in an instant. And fresh air too!” (Fig. 1). It can be inferred that “fresh air” refers to
photosynthesis-released oxygen.
There are three types of photosynthesis: C3, C4, and CAM. The typical
photosynthesis is C3 (Biology.com). This research is centered on C3, which will be
referred to simply as photosynthesis. C3 plants use direct carbon fixation into a
three-carbon compound. The catalyst for this reaction is rubisco. Most broadleaf,
temperate plants fall into this category. CO2 is taken in through the stomata during
daylight hours and converted to oxygen that is then released (Eitel, 2012). When
sunlight is not present, the plant respires and releases CO2, due to the enzymatic
oxidation of substrates.
Basic knowledge of C3 photosynthesis may lead to an acceptance of this claim
that plants add “fresh air”; however, after taking respiration into account, it is
difficult to assess the validity of this epithet. Assuming “fresh air” as a synonym for
an increase in levels of photosynthesis-released oxygen, it may be inferred that the
plants also act as a small-scale carbon sink. By determining if houseplants in fact fix
more CO2 through photosynthesis than is released through respiration, one would
be able to improve the air quality in a room simply by adding more houseplants. The
objective of this research was to determine the connection between plant presence
and net CO2 flux. The hypothesis was that the presence of houseplants would result
in a net decrease in carbon dioxide.
Methods
Research was conducted in a small semi-enclosed bathroom. The bathroom
is 8 feet by 6 feet with one window and no other ventilation. Lights were not turned
on during the course of the experiment. The door remained closed. The curtains on
the window were left open. The study was conducted over one weekend in October
and one in November during sunny to partially sunny days.
Three common houseplants (Aphelandra squarrosa, Chlorophytum comosum,
Hosta Montana) were placed in the bathroom. The plants were set-up in front of the
window. LabQuests with five (5) Vernier CO2 probes (Vernier Software and
Technology, Beaverton, OR, USA) were distributed throughout the area in which the
plants were present, ranging from 1-inch to 10-inches from the plant, resulting in
five samples. Measurements were recorded every 15 minutes over a 24-hour period.
An additional set of data was collected with no plants present.
LoggerLite software (Vernier Software and Technology, Beaverton, OR, USA)
was used to compile data and the data was graphed using the open-source software
package R 2.15.2 (R Development Core Team, 2012).
Results
A total of six datasets from three different days were collected with each
dataset subdivided into separate samples. The maximum and minimum CO2 values
ranged from 0.00 to 609.21 ppm (Table 1). Maximum CO2 value occurred in the
Treatment 5 dataset at sunrise (24 hours after) and the treatment 2 and 4 dataset
reached their maximum 0.50 hours following sunrise. Both maximums occurred
7.80 hours after sunrise Treatments 1 and 3. The maximum of the control dataset
occurred 8.00 hours after sunrise.
The measurements from this experiment did not supply enough data for any
meaningful statistical analysis. However, visual analysis of the CO2 measurements
indicates that the CO2 fluctuation is greater with the absence of plants (Fig. 1).
Table 1: Maximum and minimum concentrations of carbon dioxide measured and the times
at which they occurred, expressed as hours after sunrise.
Dataset
Max (ppm) Min (ppm)
Max
Min
Time (HAS) Time(HAS)
Treatment 1 609.21
466.54
7.80
23.75-24.00
Treatment 2 43.00
40.00
0.50
Sustained
Treatment 3 536.16
408.74
7.80
23.75
Treatment 4 24.00
0.00
24.00
0.00
Treatment 5 270.00
129.90
0.50
24.00
Control
43.49
8.00
0.0-1.50
490.57
Figure 1: Carbon dioxide concentration is shown over a 24-hour period beginning at
sunrise
Discussion
Similar studies support the theory of plants as slight carbon sinks
(Buchmann & Schulze, 1999; Janssens et al., 2001). Contrastingly, others suggest
that entire ecosystem CO2flux must be measured in order to support sink status
(Flanagan et al., 2002). On a small scale, diurnal CO2 concentration has been found
to mirror the pattern discovered in the control group of the present study (Flanagan
et al., 2002). In the present study, graphical analysis revealed an overall greater CO2
concentration with plant presence in two treatments. The others showed an overall
lower concentration when compared to the control. Results were inconclusive,
rendering the hypothesis of the present study unsupported.
As previously established, CO2balance depends on rate of photosynthesis.
Similar studies reveal that photosynthesis rate is related to time of growing season,
light availability, and soil moisture (Ainsworth & Rogers, 2007; Flanagan et al.,
2002; Taub, 2010). Treatments 1 & 3, containing the higher CO2 concentrations,
were measured in late November. The control was also measured in November. Due
to the short growing season and high altitude of the research site, these dates were
well outside the prime photosynthesis season (Love et al., 2009). This distance from
the growing season could account for the increased CO2 concentrations in these
datasets.
Measurements in this study were limited by a lack of accuracy. Currently, the
most accurate measurements of CO2 flux are obtained using eddy covariance
measurements (Baldocchi et al., 1988; Burba & Anderson, 2010; Lee et al., 2004).
Future studies could be improved by using the eddy covariance technique. Further
limitations were a small sample size and a limited time period. While this
investigation did not result in conclusive data to properly measure impact of plant
presence on net CO2 gain or loss, improved methodology could supply more results.
Furthermore, this study did not record soil moisture, temperature, or light
availability. Future studies would contain more revealing data were these
measurements to be recorded as well. Future studies on plant presence throughout
the year and growing cycle would result in better data.
In conclusion, this investigation did not reveal any significant connection
between houseplant presence and net carbon dioxide decrease. However, future
studies with improved methodology, increased sample size, and richer data
measurements, monitored over the course of a growing season, may yield
substantial results.
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