April 16, 2019
April 9, 2019
Experiments are conducted in laboratories because it is markedly easier to control conditions indoors, in enclosed systems, than out-of-doors. However, it is common that little attention is paid to changes in gaseous dynamics in enclosed environments and the consequences it can have on plants. Researchers will account for and control light conditions, soil, nutrients, water and myriad other elements in the study while entirely ignoring the atmosphere in which the plants are growing.
Many gases are found throughout a plants life cycle, including, but not limited to: carbon dioxide (CO2), oxygen (O2), nitrogen dioxide (NO2), ethylene (C2H4), and water vapor (H2O).
CO2, O2, NO2, and H2O occur naturally in the atmosphere, while ethylene is produced by plants. Each of these gases is a part of vital physiological processes in plants, and changes in their concentrations in enclosed spaces can have a considerable impact on growth, photosynthesis, and other functions. Therefore, their presence cannot be ignored when experiments are conducted with plants. Unless gases are accounted for, the data derived from experiments can be misinterpreted, confounded or invalidated entirely.
There are around 340 ppm by volume of CO2 naturally occurring in the air. In an enclosed greenhouse during experiments, the CO2 levels can fall to 200 ppm because plants use the existing CO2 for photosynthesis. As a result, the decrease in CO2 levels below ambient levels affects plant growth. Monitoring CO2 levels and then providing ventilation at predetermined intervals during the day is needed to “recharge” the carbon dioxide levels. It is important to note that monitoring is of utmost importance to ensuring that ventilation allows ambient atmosphere to reach desired levels.
Temperatures can rise in enclosed environments like growth chambers or greenhouses. In combination with high soil water content, increases in temperatures tend to lower the concentration of soil oxygen. At 400C, oxygen levels drop from the normal 8-9 ppm to 2 ppm. This can weaken plant roots and make the subjects more susceptible to root diseases. A reduction in soil oxygen also makes plants less robust. To monitor O2, CO2 and Ethylene (discussed below), check out our 3 gas analyzer.
Relative humidity levels are higher inside greenhouses due to increased temperatures, transpiration by plants and lack of ventilation.
Transpiration occurs because water pressure in leaves is higher than in the air. A decrease in the difference of pressure dampens the rate of transpiration. This is important because the stomata open during transpiration to release water vapor. When the stomata open, O2 produced during photosynthesis moves out, while CO2 necessary for photosynthesis moves in. These movements are hampered when transpiration is reduced. The loss of water vapor during transpiration also helps in the absorption of water and nutrients from the soil. Thus, when the stomata remain closed due to high humidity, many crucial processes in the plant are affected.
When present in small amounts, NO2, a trace atmospheric gas, is beneficial for plant growth and development. However, when the concentration increases to 120 µg/m3, plants can experience inhibited growth. Additionally, if either ozone or sulphur dioxide are present in the enclosed atmosphere, these conditions can lead to the formation of acidic precipitation, which is detrimental to plants.
Ethylene (C2H4) is produced by all plants during periods of active growth and remains constant or decreases during seed and fruit formation. In enclosed areas, ethylene concentrations can accumulate, resulting in increased aging speed of plants, yellowing of leaves, and abscission of leaves and flowers. Therefore, care should be taken to both monitor and remove ethylene from the rooms. Check Felix Instruments' portable ethylene analyzer here.
Many researchers, to the detriment of their experiments, ignore the impact gases can have on their plant studies. Given the physiological processes these common gases influence in plants, researchers must monitor and control for the confounding effects they can cause. For more information on tools to help monitor and control for gas concentrations, visit www.FelixInstruments.com.
Science Writer, CID Bio-Science
Ph.D. Ecology and Environmental Science, B.Sc Agriculture