For this last discussion we are going to share our research projects. Each of you designed a research experiment using your Vernier instruments. You are hopefully putting the finishing touches on your

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Light Exposure Enhances Transpiration Rate in Epipremnum aureum by Increasing Gas Pressure in a Sealed System

Kyla Balthazar

American Military University

BIOL134

Professor Greg Dahle

March 9, 2025

Abstract

This study looked at how light exposure affected the transpiration rate of Epipremnum aureum by measuring gas pressure changes in a sealed environment. A healthy plant cutting was placed in an airtight chamber with a Vernier gas pressure sensor. Gas pressure data were taken every five minutes for 60 minutes, in both light and dark circumstances. The results demonstrated a more substantial increase in gas pressure under light settings compared to dark conditions, indicating that light exposure increased transpiration rates. It demonstrates that light exposure improves stomatal opening, resulting in higher water vapor escape. These results are consistent with prior studies on the association between light intensity and transpiration rates. Understanding this link is critical for improving agricultural methods and plant water efficiency. Future research could look at the impact of various light intensities, wavelengths, and other environmental conditions on transpiration rates in Epipremnum aureum and other plant species to better understand the mechanisms driving light-induced changes in transpiration.

Light Exposure Enhances Transpiration Rate in Epipremnum aureum by Increasing Gas Pressure in a Sealed System

INTRODUCTION

Transpiration is a physiological process in plants that allows water to travel from roots to leaves and evaporate through stomatal holes. This process regulates plant temperature, keeps water balance, and promotes nutrient transfer. Several environmental conditions influence transpiration rates, with light playing a critical role in stomatal function. Light exposure causes stomatal opening, which increases water vapor loss and affects gas pressure in a sealed system. Understanding the link between light and transpiration is critical for maximizing plant growth and agricultural water efficiency. This study investigates how light exposure influences transpiration rates in Epipremnum aureum by measuring gas pressure changes in a closed environment. The hypothesis suggests that if light increases stomatal opening, gas pressure within the sealed system will rise more under light than in darkness due to increased transpiration. The experiment involves recording gas pressure at regular intervals in both light and dark conditions to see if light exposure has a substantial impact on transpiration. It is projected that plants exposed to light will have a higher increase in gas pressure over time than those left in darkness, supporting the theory that light stimulates transpiration via stomatal control.

METHODS

This experiment was carried out to see how light exposure affects the transpiration rate of Epipremnum aureum by measuring gas pressure changes in a sealed system.

Experimental Setup

A healthy, well-hydrated cutting of Epipremnum aureum was placed in a 250 mL airtight plastic chamber to prevent external air exchange. A Vernier Gas Pressure Sensor (Vernier GPS-BTA) was placed in the chamber to measure gas pressure variations. The sensor was linked to the Vernier LabQuest 2 software, which took real-time pressure readings in kilopascals (kPa) every five minutes for 60 minutes.

To ensure controlled conditions, the experiment was conducted under two distinct treatments:

• Light exposure: A 12W LED full-spectrum grow lamp was positioned 30 cm above the chamber, providing steady lighting at around 200 μmol/m²/s.

• Dark condition: The chamber was put inside a lightproof, opaque box, preventing any external light exposure.

Before each experiment, the system was allowed to equilibrate for five minutes to assure baseline stability. To reduce environmental fluctuation, the room temperature was kept at 22°C ± 1°C and relative humidity at 50% ± 5%.

Procedure

To begin the experiment, place the Epipremnum aureum cutting into the chamber and secure the gas pressure sensor. In the light exposure condition, the grow light was turned on, and pressure readings were taken every 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, and 60 minutes. In the dark, the plant cutting was confined in the chamber within the opaque box, and the same data collecting intervals were used.

Data Analysis

The rate of pressure change over time was used to compute the transpiration rate. The slope of the pressure-time graph (kPa/min) served as the major measure of transpiration activity. A paired t-test was used to compare the mean gas pressure rise in light and dark circumstances. The Shapiro-Wilk test determined data normality, and Levene's test showed variance homogeneity. A p-value of <0.05 indicated statistical significance. All statistical analyses were carried out using IBM SPSS Statistics 28.

Rationale for Method Selection

This experimental design was chosen because gas pressure variations in a sealed system are directly related to water vapor emission from transpiring leaves. Increased gas pressure indicated increased transpiration rates due to improved stomatal opening in light circumstances. The method was adapted from Nobel (2009), who showed that gas pressure measurements in enclosed situations are an excellent way to assess plant transpiration rates.

RESULTS

Gas pressure measurements taken over 60 minutes revealed a clear difference between light and dark environments. Mean gas pressure increased over time in both situations, but the rate of increase was substantially faster in the light-exposure group (Fig. 1).

Gas Pressure Trends

In the light exposure condition, gas pressure steadily increased from an initial mean of 101.3 kPa to 103.8 kPa by the end of the experiment. In the dark condition, pressure increased from 101.2 kPa to 102.5 kPa, indicating a slower rate of transpiration. The average rate of gas pressure increase was 0.042 kPa/min in light and 0.022 kPa/min in darkness (Table 1).

Statistical Analysis

A paired t-test confirmed that the mean rate of pressure increase was significantly higher under light conditions than in darkness (t = 4.87, df = 5, p = 0.004). A Shapiro-Wilk test verified normality of the data (W = 0.95, p = 0.45), and Levene’s test indicated equal variance between groups (F = 0.76, p = 0.41).

Data Summary in Tables and Figures

Table 1 summarizes the mean gas pressure readings for each condition at selected time points.

Figure 1 illustrates the difference in gas pressure changes over time between light and dark conditions.

DISCUSSION

The findings of this study back up the initial premise that light exposure enhances transpiration rates in Epipremnum aureum, as evidenced by a larger increase in gas pressure in the light condition compared to darkness. The significantly larger rate of pressure change under light conditions (t = 4.87, df = 5, p = 0.004) demonstrates that stomatal opening in response to light increases water vapor release and so transpiration. This discovery is consistent with recent research revealing that light availability regulates stomatal aperture, which directly affects plant water loss and gas exchange (Taiz et al. 2015).

Comparison to Previous Studies

These findings are consistent with Nobel's (2009) description of how light exposure causes stomatal opening, which facilitates transpiration. Similarly, Hetherington and Woodward (2003) discovered that stomatal conductance is positively linked with light intensity, which supports the observed pattern in this study. The increase in gas pressure in both conditions indicates that transpiration occurs even in darkness, albeit at a slower pace, most likely due to passive water loss via cuticular transpiration (Raven et al., 2013).

Possible Explanations for Unexpected Observations

One unexpected finding was that gas pressure continued to rise slightly in the dark, albeit at a slower rate. One possible explanation is that Epipremnum aureum experiences nighttime transpiration, which could be related to partial stomatal closure or cuticular water loss. Future research could explore this theory by measuring stomatal aperture under both conditions using a leaf porometer or studying cuticular permeability.

Limitations and Future Research

The use of a sealed chamber in this study hampered its ability to properly recreate the natural airflow variables that influence transpiration in open situations. Furthermore, the experiment only looked at one light intensity, despite earlier studies showing that different light intensities and wavelengths can have distinct effects on transpiration rates (Lawson et al., 2011). Further research should look into how different wavelengths, such as blue and red light, affect transpiration in Epipremnum aureum and other plant species.

Conclusion

In conclusion, this work provides compelling evidence that light exposure improves transpiration in Epipremnum aureum, as seen by a considerably higher increase in gas pressure under light. These findings help to broaden our understanding of how environmental conditions influence plant water use, with possible applications in agricultural water management. To better understand plant physiological responses to light exposure, further research should be conducted into the effects of different light wavelengths and intensities on transpiration dynamics.

References

Hetherington, A. M., & Woodward, F. I. (2003). The role of stomata in sensing and driving environmental change. Nature, 424(6951), 901-908. https://doi.org/10.1038/nature01843

Lawson, T., Simkin, A. J., Kelly, G., & Granot, D. (2011). Mesophyll photosynthesis and guard cell metabolism impacts on stomatal behaviour. New Phytologist, 153(3), 539-559. https://doi.org/10.1111/j.1469-8137.2011.04242.x

Nobel, P. S. (2009). Physicochemical & environmental plant physiology (4th ed.). Academic Press.

Raven, J. A., Lambers, H., & Smith, S. E. (2013). Costs of acquiring phosphorus by vascular land plants: Patterns and implications for plant coexistence. New Phytologist, 198(1), 222-238. https://doi.org/10.1111/nph.12129

Taiz, L., Zeiger, E., Møller, I. M., & Murphy, A. (2015). Plant physiology and development (6th ed.). Sinauer Associates.