The Effect of Wind Strength on Transpiration Rate

 

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.