ABSTRACT
The
purpose of this study was to measure how wind strength effects the transpiration
rate in a random garden plant. A laurel
bush was selected for the experiment, whose branches were separated from the
bush and shaped to fit inside a gas pressure sensor. A fan was also used at various speeds to
imitate the effect of wind on the plant in a natural environment. Results of the experiment indicated that wind
strength has a moderate effect on transpiration rate, but only at low speeds. These results suggest that in a natural
environment, wind plays an important role in the transpiration rate of plants.
INTRODUCTION
Transpiration is a process that
signifies growth and metabolism in a plant by diffusing water through its
leaves. Specifically, it involves the
loss of water in the leaves to the atmosphere through stomata (Clark et al,
2020). Factors that influence
transpiration are light intensity, humidity, temperature, and wind speed, which
is the focus of this study. Kelly et al
(2013) state that guard cell osmolarity leads to the opening and closing of
stomata, balancing the demand for CO2 in photosynthesis with the loss of
water. Kelly et al (2013) also found
that the increased expression of an enzyme called hexokinase was responsible
for the closing of stomata after sufficient sugars are processed from
photosynthesis in the leaf. Since wind
contributes to evaporation, plants react by increasing their transpiration
(Odle) to accommodate the imbalance, leading to more rapid plant growth. However, there is a point where the wind
speed will be too great for the leaf to experience transpiration. Schymanski (2016) states that transpiration
rates “may decrease with increasing wind speed at high stomatal
resistances”. Results from Dixon &
Grace’s (1984) study indicate that this point depends on the species of plant
being studied, though there is unanimous agreement that ultra-high winds may
damage all leaves, regardless of the species.
For this
study, laurel twigs were used to measure the effect wind has on transpiration
rate. The question was: to what degree does
wind strength improve the transpiration rate of a laurel twig? It was anticipated that under light wind
strength, the laurel twig will likely experience a higher transpiration rate
than it otherwise would. Under higher levels
of wind strength, it was predicted that the transpiration rate would decrease due
to higher stomatal resistance.
METHODS
To
demonstrate the effect wind speed has on transpiration, four twig samples were
used to measure the effect wind would have at different speed settings of a
fan. The twigs were each shaped to fit
inside an aqueous tube that channeled diffusion to a gas pressure sensor connected
at the other end. In turn, the sensor
was connected to a computer program that measured the quantity of any diffusion
taking place.
The gas
pressure tube was filled with water for each trial run. Careful inspection was made for air bubbles,
which needed to be extracted from the tube for diffusion to take place. Each trial was held in a lighted area under
the same conditions. The control sample was
not to experience any air movement from the fan, while each of the other
samples would experience increasing wind speeds at different settings (low,
medium, high). The distance from the fan
to the apparatus remained constant, at about 130 centimeters.
It took a few trial runs to practice using the apparatus, so the image below is not 100% accurate. Later it was found that the sensor on the bottom right needed to be elevated on the ring stand for diffusion to take place.
RESULTS
On the
control run, the first trial was much higher than the others, at -.337kpa/15s. The second trial was much lower than others,
at -.295. The third trial ended up being
right near the average at -.314. The
average rate of transpiration for the control was .315, the lowest of all the
trials. All data can be found in table 1
below.
On low
speed, rates were similar to the control, only differing by .001 on
average. The runs were more consistent
though, going from -.324 to -.316 to -.308, signifying a lowering trend. Average rates on low speed were much lower
than those on medium and high speeds.
On
medium speed, the average rate of transpiration was the highest on average, at
-.370. The first run was near the
average at -.372. The second was below
average at -.351; the third was above average at -.386.
At high
speed, the average rate was lower than on medium but significantly higher than
on low. The first two runs were nearly
identical, averaging -.347. The third run
brought the average down by a heavy margin, showing -.322.
|
Wind strength |
Rate of transpiration (kPa/15s) |
Average rate of transpiration (kPa/15s) |
||
|
Trial 1 |
Trial 2 |
Trial 3 |
||
|
Control- no speed |
-.337 |
-.295 |
-.314 |
-.315 |
|
Low speed |
-.324 |
-.316 |
-.308 |
-.316 |
|
Medium speed |
-.372 |
-.351 |
-.386 |
-.370 |
|
High speed |
-.348 |
-.346 |
-.322 |
-.348 |
Table 1. Trials and runs for wind strength on transpiration rate. Wind strength was imitated using a fan at different speed settings. The trials show that as wind speed increases, so does the transpiration rate, but only before an optimal speed is reached. At optimal wind speed, the plant maximizes its transpiration rate to balance the effect of wind increasing evaporation on its leaves.
DISCUSSION:
Results indicate that wind strength significantly
impacts transpiration rates for the laurel bush. There was about a 15% increase in
transpiration from the control to the maximal rate at medium speed. The data supports other findings that plants
compensate for wind-caused evaporation by increasing photosynthesis, thus
increasing transpiration in turn (Odle; Kelly et al, 2013). Results also suggest the effect decreases
with higher wind speeds (Schymanski, 2016), as the high-speed trial indicated a
6% decrease in transpiration rate from the medium trial.
It would have been more evident with
a fifth trial at wind a speed greater than “high”, or if I had simply moved the
fan closer to the apparatus. The low-speed
trial would have likely shown higher transpiration rates, with medium and high
speeds showing a downward trend as air movement gets too high to compensate for
the loss of water on the surface of the leaves.
Data showing a continuous downward trend would be ideal to illustrate
what is going on better. Another change
I would make is ensuring there are no air bubbles in my initial trial run, as
that may have skewed the control average.
Future research should examine the effects of higher wind speeds to see
at what point stomatal resistance reaches 100%, or how the plant reacts to
being different distances away from the fan.
REFERENCES
Clark, M.A., Choi, J., & Douglas,
M. (2020). Biology 2e. OpenStax.
Rice University.
Dixon, M, Grace, J. (1984).
Effect of Wind on the Transpiration of Young Trees, Annals of
Botany, 53(6), 811–819, Retrieved December 5, 2021, https://doi.org/10.1093/oxfordjournals.aob.a086751
Kelly, G, Moshelion, M., David-Schwartz,
R., Halperin, O, Wallach, R., Attia, Z., Belausov, E., Granot, D. (2013). Hexokinase mediates stomatal closure. Plant
J. 2013 Sep;75(6):977-88. doi: 10.1111/tpj.12258.
Odle, Teresa. How Does Wind Affect Transpiration? Plant Addicts.
https://plantaddicts.com/how-does-wind-affect-transpiration/
Schymanski, S. J., &
Or, Dani. (2016) Wind increases leaf water use efficiency. Plant,
Cell & Environment, 39: 1448– 1459. doi: 10.1111/pce.12700.
