The Functions of Stomata and the Structure of Guard Cells

close-up photo of green-leafed plant
October 01, 2020

Photosynthesis is integral to the life of your marijuana plants. Apart from the sun, water, and nutrients, this process also involves different plant parts functioning as a “team.” Unknown to many, stomata also plays an integral role. Are they simply a part of cannabis leaves that serve as a means for transpiration, or do they have other critical purposes? By the time you finish reading this article, you will realize that there is more than meets the eye when it comes to these tiny openings. And that you can put the knowledge gained to good use when optimizing the growth of your plants.

What Are Stomata?

Stomata (singular “stoma”), also called stomates (singular “stomate”), are tiny pores found mainly on the outermost layer of leaves and also in stems. Think of them as windows where wind can pass through. Their primary role is to facilitate gas and moisture exchange.

This critical function facilitates photosynthesis by allowing light to enter, uptake carbon dioxide, and release oxygen. Open stomata are necessary for the plants to complete the photosynthetic process. However, they also lose up to 99% of the water absorbed by the root system through these openings. Considering that dehydration could be a severe problem, the plants are not entirely helpless. They do have the ability to close the pores if the situation warrants.

Through thousands of years of evolution, the plants have adapted well to the environment, able to strike a balance between opening and closing their stomata. But you can intervene by tweaking the conditions to influence when that happens to optimize growth, bud quality, and final yields.

What Are Guard Cells?

Surrounding a stoma are two guard cells. If stomata are windows, then they are the opening and locking mechanisms. Depending on environmental conditions or chemical signals, they react by opening or closing the pore.

Guard cells assimilate sugar and potassium whenever there is an adequate level of light and carbon dioxide. The increase in solutes causes an influx of water molecules. As the cells increase in volume, they reveal the opening of the stoma, which now allows for gas and moisture exchange. As you can see, they are responsible for striking a balance between light, CO2, and water while ensuring that the plant is not dehydrated.

How important is CO2 when growing marijuana? The answer to that is very, particularly in terms of photosynthesis.

Usually, the process of opening and closing the stoma takes only a few minutes. In some cases, it might take hours. That happens whenever there is a deficiency in solutes, such as potassium.

What Is the Stomata’s Relationship with Light, CO2, and Water?

Stomata open up or close in response to light and CO2, both elements necessary for photosynthesis. Once they are open, moisture seeps out into the air. And if there is any danger of dehydration, the plant responds by signaling the guard cells to close the stomata.

Keep in mind that dehydration is not necessarily due to losing moisture in the air. It could also be a result of the lack of water in the medium. Furthermore, other atmospheric conditions that increase the rate of transpiration should be taken into consideration.

In a situation where the heat is excessive, the capacity of air to hold moisture is higher. The relative humidity (RH) also drops, indicating less moisture. All these combine to make the plants transpire more, and that is how they start losing more water.

Another condition that may lead to dehydration is when it is too windy. Because the plants keep losing water vapor that clings to the leaves’ surface, they have to transpire more.

The loss of water in the xylem – one of the plant’s two transport tissues – leads to wilting. You would see the leaves and stems lose turgor. By then, the plants would have responded by closing the stomata to prevent further loss.

The blue end of the color spectrum appears to influence larger openings, more so than red. Some people think that mixing some blue LEDs during the flowering period might be worth trying. The idea is to manipulate the guard cells into maximizing the openings to allow for a better flow of CO2. That is unproven, and it could even disrupt the optimization system of the plant.

The size of the pores depends on the light’s intensity. The more light, the larger the size of the openings. Interestingly, the concentration of CO2 in the leaves diminishes as the intensity increases. The guard cells react to diminished CO2 by absorbing more and maintaining a balance between the internal and external CO2 levels.

Too much CO2 in the environment, however, leads to smaller stomata openings. It can potentially cause overheating and yellowing leaves. For this reason, you should keep the CO2 level in the grow room at around 1500 ppm if you use a generator. Moreover, make sure that there is proper air circulation.

You will need to consider CO2 levels when thinking about how to successfully grow huge cannabis buds as it has a big impact on yields and the plants overall growth.

Make the Guard Cells and Stomata Work for You

Guard cells are responsible for opening and closing the stomata. They work as a result of environmental conditions, including light, CO2, and water. Understanding how this whole mechanism works and why they are essential to the photosynthetic process is fascinating. But you can use that knowledge to your advantage. At the very least, you should ensure that they function as intended.

You can also better enhance growth by providing what they need to perform their roles. For example, providing the right level of CO2 during the daytime hours. At the same time, realizing that the plants are losing moisture into the air, you should ensure that the medium contains an adequate supply of water. Furthermore, monitor the temperature and humidity levels. By keeping these conditions optimal, you can let the stomata function best, fulfilling their role in energy production that the plants need to thrive.