The Investigation of How Light and Relative Humidity affects Transpiration Rate

The Investigation of How Light and Relative Humidity affects Transpiration Rate

Transpiration in plants is one of the essential and exciting processes that occur in the various parts of the plants. The transpiration process refers to the movement of water from the roots of the plant and across the various parts of the plant until the tip of the plant, which is the leaves. Transpiration can, therefore, be said to be the process through which plants transport water from the roots to the leaves and the ultimate loss of water into the atmosphere through the leaves. The water potential is one of the significant influencers of the movement of water from the root tissues through the xylem to other parts of the plant, including the leaves. According to Kerr Shana (2016, p. 1), water potential refers to the potential energy contained in water movement between two bodies. The water molecules move from the higher water potential areas (roots) to the lower water likely regions of the plant (leaves) is affected by light and relative humidity.  Therefore this study explores the extent at which light and relative humidity affect reparation rates in plants.

Mechanism of Water Movement in Plants

The movement of water from the roots up to the leaves of the plant includes the operation of against the gravity. The water movement phenomenon from the roots across the xylem parts of the plant engages the three key concepts, which includes root pressure, capillary action and cohesion tension. The root pressure is responsible for pushing water molecules up from the roots. On the other hand, capillary action is attributed to pulling water up inside the xylem against the gravity force. Lastly, cohesion tension is centred on drawing water molecules up the xylem. Therefore, the xylem tissues are the critical parts of the plant that necessitate the transportation of water to the leaves, which accounts for the most significant water loss.

However, the determinants of the degree at which the plant losses water to the environment via transpiration in a reasonable condition include the driving force and the resistance. The driving force in the transpiration process provides for the availability of water in the soil and the air. In that, as the humidity of air and the amount of water contained in the soil varies, so does the driving force for transpiration. On the other hand, the resistance to the movement of water in a system is reliant on the three main factors. The factors encompass: 1) the type of the plant and the resistance to the movement inside the roots, stems as well as the leaves: 2) The soil type and opposition to the flow of water: and lastly, 3) the resistance within the air to the flow of water vapour. Therefore the rate of transpiration is the driving force per resistance (Doc 5).

Rate = Driving Force/Resistance

The environmental factors specifically humidity and light (temperature) significantly impact the rate of transpiration. For instance, Agata, Hakoyama, and Kawamitsu, (1985, p. 130) report that the rate of transpiration is significantly increased by the increase in the light intensity. Similarly, Pantin and Blatt (2018, p. 485) posit that the higher the humidity in the air, the lower the transpiration and vice versa. The study suggests that the dry air offers a large gradient in water vapour through the stomatal pore (vapour pressure deficit (VPD) through the stomata pore enhanced by diffusion.

Alternative Hypotheses

H1: the increase in light intensity results in the rise in the rate of transpiration in plants

Justification: the study by Tang et al., (2019, p. 97) exposed that there is a tremendous positive impact on the rate of respiration for soybeans and sunflower.

H1: the decrease in humidity results to the increase in the rate of transpiration in plants

Justification: the study by Oksanen et al., (2018, p. 317) revealed that the plants’ respiration rate was negatively impacted by increased relative humidity in Estonia.

Methodology

• The initial stage of the experiment is conducted in the room with dim light. Overhead lights are turned off.
• Astra, herbaceous plants are used for the experiment having been stored for at least 24 hours. Moreover, their roots are free from any soil and are hydrate by placing them in water.
• The plants are stored in the 125-mL flask with 100 mL of distilled water, and the leaves are sealed on the flask with some paraffin to stop wetting the leaves
• The data are recorded in the table form.

In phase 1 of the experiment the plant was placed on the balance, and the weight was recorded while the lights are off. The relative humidity was recorded, and at the end of the 25 min period, weight of the plant was again taken. In phase 11, the recorded weight of the phase 1 experiment was used as the initial weight of the plant. The lights were turned on, and the relative humidity was taken. After a 25 min period, the weight of the plant was again recorded and use as the initial weight of phase 111. In phase 111, the tents were removed around the plants and humidifier turned off. The hair dryer was employed to dry the place. Finally, the relative humidity was measured and recorded as well as the weight of the plant after a 25 min period.

It is important to note that the experiment involved the sample size of 13 plant leaves per treatment. The initial weight refers to the weight recorded before the treatment begins at every phase of the treatment and the final weight refers to the weighed recorded after the treatment. The change in weight refers to the difference in the final and initial weights.

Change of weight (g) = initial weight (g) – final weight (g)

Transpiration rate refers to the product of the change in weight by leaf area per a given time

Rate of Transpiration = change in weight (g) x leaf area (cm2)/ time (min-1).

Finally, the area of the leaf was measured and recorded. The leaves were cut using the scissors. The leaves were then traced on the blank sheets of paper, and the leaf traces were cut out. The cut-outs were then weighed. The same type of blank paper was cut into a square piece of 10cm x 10cm = 100cm2.

The formula for leaf are: Leaf area (cm2) = weight of leaf cut-outs (g) x 100 cm2/ weight of 100 cm2 paper (g).

Results of the Study

Graphical presentation of transpiration rate

The mean and Std. Dev. for high humidity, dark encompassed in treatment 1 was 1.74758E-05 and 1.74227E-05 respiration rates, respectively. For treatment/ phase 11, which involved high humidity and light registered the mean and std. Dev. of 2.63464E-05 and 1.70893E-05 respiration rates respectively. Lastly, the mean and std. Dev. for low humidity and light recorded 5.15147E-05 and 4.65437E-05 transpiration rates respectively. The data reveals that indeed increased light and low humidity results in increased respiration rates.

Discussions

Transpiration is an important process for the plants’ life. However, the transpiration rate is influenced by various environmental factors, with the main one being light and humidity. The three experiments have succeeded in underpinning that indeed the presence of light or light intensity has a positive impact on the rate of transpiration. The results of the study are in agreement with the positions portrayed in the study conducted by Tang et al. (2019, p. 97). Tang et al. (2019, p. 97), suggested that there was a positive link between light intensity and the respiration rate for soybean and sunflower. The deductions from the study indicate that light intensity is one of the main causes of increased respiration rates in plants. Moreover, the study recorded an increase in the respiration rate when the light was introduced, and the relative humidity reduced. Agata, Hakoyama, and Kawamitsu share similar views (1985, p. 130).

The transpiration rate is also significantly impacted by the decrease in humidity. The study reveals that there was a significant reduction in the rate of respiration in the absence of light and increased humidity levels for the plants. Similar sentiments are shared by Pantin, F., & Blatt, M. R. (2018). The study by Pantin, F., & Blatt, M. R. (2018) reiterated that the increase in relative humidity in the external of the plant leaves leads to the reduced respiration rate. The reduction in respiration rates is attributed to the wet atmosphere resulting in a small gradient in water vapour between the stomata pores.

Reference

Agata, W., Hakoyama, S. & Kawamitsu, Y. (1985). Influence of light intensity, temperature and humidity on photosynthesis and transpiration of Sasa nipponica andArundinaria pygmaea . Bot Mag Tokyo 98, 125–135. Retrieved on 29 April 2020 from https://doi.org/10.1007/BF02488792

Kerr Shana (2016).Water Transport in Plants: Xylem. Biology 1520-Georgia Tech Biological Sciences. Retrieved on 29 April from http://bio1520.biology.gatech.edu/nutrition-transport-and-homeostasis/plant-transport-processes-i/

Oksanen, E., Lihavainen, J., Keinänen, M., Keski-Saari, S., Kontunen-Soppela, S., Sellin, A., & Sõber, A. (2018). Northern forest trees under increasing atmospheric humidity. In Progress in Botany Vol. 80 (pp. 317-336). Springer, Cham.

Pantin, F., & Blatt, M. R. (2018). Stomatal response to humidity: blurring the boundary between active and passive movement. Plant physiology, 176(1), 485-488.

Tang, M., Cheng, W., Zeng, H., & Zhu, B. (2019). Light intensity controls rhizosphere respiration rate and rhizosphere priming effect of soybean and sunflower. Rhizosphere, 9, 97-105.