BIOLOGY – 479 INTEGRATED PHYSIOLOGY LABORATORY
Dept. of Biological & Allied Health Sciences
BLOOMSBURG UNIVERSITY of PENNSYLVANIA
LAB REPORT: PHOTOSYNTHESIS AND LIGHT
Michael Tekin
Lab section:
02A, Tuesday 21, 1400 – 1650
Relationships between CO2 Assimilation and Light Intensity
8
CO2 Assimalation (mmol m-2 s-1)
7
y = 0.004x - 0.9181
R² = 0.9812
6
5
4
3
2
1
0
0
500
1000
Light Intensity
(umol*m-2*sec-1
1500
2000
)
Figure 1. CO2 assimilation of parade roses was measured at different light intensities. The equation of the trend
line produced form these data was y = 0.004x - 0.9181. There appears to be a linear trend between CO2
assimilation and light intensity (R² = 0.9812).
Figure 1 demonstrates a linear trend for CO2 assimilation and light intensity. The R2 indicates the
equation determined from this trend line is accurate (R2 =0.9812, fig 1.). The Y intercept should
be slightly negative, because CO2 is being used due to respiration, while no photosynthesis is
occurring (Devlin et al. 1983). Thus, the -0.9181 mmol0m-2s-1 CO2 assimilation rate at zero light
exposure, predicted by Figure 1, is not unexpected. Also, the expected expect shape of the trend
between CO2 Assimilation and light intensity was a hyperbolic growth (Kim et al. 2003).
However, the roses (Rosa hybrida L.) may of never reached photosaturation. Photosaturation is
when the rate of photosynthesis reaches its max capacity despite increasing light input (Devlin et
al. 1983). This indicates 2000 umol m-2*sec-1 is not a high enough of a light intensity to cause
photosaturation. This however seems unlikely because the expected light intensity for
photosaturation was about 1000 umol*m-2*sec-1, with a CO2 assimilation rate of 20 mmol m-2 s-1
for rose leaves that are 30 days old roses (Kim et al. 2003). However, the maximum measured
CO2 assimilation rate was 7.11 mmol m-2 s-1 at a light intensity of 1949 umol*m-2*sec-1. One
possible reason this occurred was the roses used were not exactly 30 days old, so the maximum
CO2 assimilation rate will probably not be exactly the same. Moreover, the sample size is one
rose leaf, so sampling error is a definite possibility. Additionally, the reason photosaturation was
not seen was probably due to the light sensor calibration methods. The 2000 umol m-2*sec-1 of
light calibration was not set using a known light intensity. It was set when the sensor was just
about oversaturated with light intensity. Thus, if the two point calibration of the light sensor was
inaccurate, the light intensity measured was also inaccurate. Therefore, if the 2000 umol m-2sec-1
calibration was too low, all of the measured light intensities would also be too low. Then the
plant may have never received enough light intensity to be photosaturated, even if the measured
light intensity said it should.
Relationships between Evapotranspiration and Light Intensity
Evapotranspiration ((mol/(m2s))
0.03
0.025
y = 2E-05x - 0.0095
R² = 0.9284
0.02
0.015
0.01
0.005
0
0
500
1000
Light Intensity
1500
(umol*m-2*sec-1
2000
)
Figure 2. Evapotranspiration of parade roses was measured at different light intensities. The equation of the
trend line produced form these data was y = 2E-05x - 0.0095. The trend between evapotranspiration and light
intensity could either be linear (R² = 0.9284) or exponential.
The R2 indicates the equation calculated from linear trend between evapotranspiration and light
intensity is accurate in Figure 2. However, Figure 2 could also be an exponential trend. To
confirm one oppose to the other, evapotranspiration would need to be measured at higher light
intensity. However, it was expected that the trend between evapotranspiration and light intensity
would demonstrate hyperbolic growth (Devlin et al. 1983). This is because the rose would
eventually reach a maximum evapotranspiration rate. Again, this could be because the light
intensity was not strong enough for this to occur, and the poorly done calibration explained
above.
Relationships between Evapotranspiration and CO2 Assimilation
CO2 Assimalation (mmol m-2 s-1)
8
y = 226.01x + 1.4283
R² = 0.9683
7
6
5
4
3
2
1
0
0
0.005
0.01
0.015
Evapotranspiration
0.02
0.025
0.03
((mol/(m2s))
Figure 3. Measured CO2 assimilation of parade rose was graphed over evapotranspiration of parade roses. The
equation of the trend line produced form these data was Y = 226.01x + 1.4283. There appears to be a linear trend
between evapotranspiration and CO2 Assimilation (R² = 0.9683).
Figure 3 demonstrates a linear trend between CO2 assimilation and evapotranspiration. The
expected trend between CO2 assimilation and evapotranspiration is also linear, because both were
expected to follow a hyperbolic trend when exposed to increasing light intensity (Kim et al. 2003, Devlin
et al. 1983). However, neither Figure 1 nor Figure 2 followed the expected trends. Therefore, it is
inclusive if Figure 3 is following the expected trend because it is accurate, or because Figure 1
and Figure 2 had a linear trend. Moreover, these data are potentially inaccurate because of the
calibration problem explained earlier.
Fluorescence experiment
Methods
The following methods were obtained from William 2013: The plants used for this
experiment was primroses. The ages of the primroses were all about the same. The primroses
were divided into two groups. One group of primroses was treated with paraquat while the other
group was a negative control. Both groups were then dark acclimated for thirty minutes using a
slide that covered the leaf. Then, the fluorescence of each group was measured using a
fluorescence meter.
The fluorescence meter measured F0, FM, FV/FM, and T1/2. These values were then
recorded. The sample size for both the control and the paraquat treatment was eighteen.
Results
0.795
0.79
0.785
FV/FM
0.78
0.775
0.77
0.765
0.76
0.755
0.75
paraquat
Treatment
control
Figure 4. The FV/FM of primroses treated with paraquat and control was measured. The primrose treated with
paraquat had a significantly lower FV/FM than the FV/FM of the control treatment (T=0.986,df = 35,p=.018).
The Fv/Fm for the paraquat treatment was significantly less than the control treatment
(T=0.986,df = 35,p=.018).
Discussion
FV/FM can be used to determine the amount of CO2 being absorbed by a leaf and a low FV/FM
can indicate stress (Williams 2013). Moreover paraquat is a known to be toxic for plants
(Medline 2014). Hence, if any light dependent or light independent reaction is inhibited, the
FV/FM will be lowered. Thus, paraquat could have decreased FV/FM because it is inhibits for one
of these reactions. For example, if paraquat inhibited RUBISCO the FV/FM would be decreased.
However, further experimentation is necessary to determine the exact mechanism that causes
paraquat to be toxic and decrease FV/FM.
Are Parade Rose C3 or C4
C4 plants do not become photosaturated, have a water use efficient of 4-12 mmol H20 /mole CO2 ,
and a light compensation point around 50-100µE. C3 plants become photosaturated at 33.3% of full
sunlight or less, have a water efficiently of 2-5 mmol H20 /mole CO2, and have a light compensation point
of 0-30 µE (William 2013). According to this experiment the rose buds were not photosaturated. The
water efficiency of the parade roses was 226 mmol H20 /mole CO2. Although this value is not the most
accurate because it was calculated from potentially inaccurate data, for reason explained previously, it
still can be inferred the water efficiency for this plant is high. Last the light compensation calculated to be
230 µE using Figure 1. Again, this may not be an accurate value due to potentially inaccurate data were
used, but the value does indicate a high light compensation. All of these values indicate the rose used is a
C4 plant. However, since these numbers may not be entirely accurate (see results above), saying this plant
is C4 may also not be entirely accurate.
Nitrogen use of C3 and C4 plants
6A) Nitrogen must indirectly play a role in photosynthesis and thus becoming a limiting factor
on photosynthetic rates. Since nitrogen is not directly used in photosynthesis but is used in
enzyme necessary for photosynthesis and CO2 assimilation (Devlin et al. 1983). Thus as enzymes
increase so would the amount of CO2 assimilation that occurs at photosaturation.
6B)
C4 plants have higher photosynthetic nitrogen use efficiency than C3 plants (Ripley et al. 2008).
Thus, at low levels of CO2 and nitrogen they will have higher photosynthetic rates.
6C) C3 plants have more RUBISCO than C4. Thus, they will have higher CO2 assimilation than
C4 plants at higher CO2 levels.
Work cited
Devlin , R. M., and F. H., Withnam. 1983. Plant Physiology 4th ed., Willard Grant Press,
Boston, USA.
Kim, S. and J. H. Lieth. 2003. A Coupled Model of Photosynthesis, Stomatal Conductance and
Transpiration for a Rose Leaf (Rosa hybrida L.). Annals of Botany 91: 771-781
Ripley, B. S., T. I., Abraham, and C. P. Osborne. 2008. Consequences of C4 photosynthesis for
the partitioning ofgrowth: a test using C3 and C4 subspecies of Alloteropsis
semialata under nitrogen-limitation. Journal of Experimental botany 59(7):1705-171
. Williams, Kevin. 2013. Photosynthesis. Pages 1-25. Lab Manual for Integrated Physiology
Laboratory. Bloomsburg University of Pennsylvania, Bloomsburg, PA.