Greenhouse Gases

Karen Delahaut, Outreach Specialist, UW-Madison

There are several gases that can impact plant growth in a greenhouse. In the case of carbon dioxide, it can either benefit or damage plants depending on the concentration. Ethylene, ozone, and sulfur dioxide are all injurious to many greenhouse plants. It is important that you keep this in mind when trying to diagnose a plant problem—it may not be caused by a disease or insect pest but by one of these abiotic factors.  Poly-covered greenhouses are more airtight than greenhouses constructed of glass and hence are more prone to damage by accumulated gases.  

Carbon dioxide (CO2) is considered an essential component of plant growth. Through photosynthesis, plants use water and carbon dioxide to produce carbohydrates. CO2 levels of 300ppm are generally what are needed for good plant growth, while levels above 1200ppm can become injurious. CO2 deficiency can occur in greenhouses that are closed up in winter to conserve heat. When CO2 is limiting, plant growth slows resulting in stunted plants and delayed maturity. Conversely, too much CO2 will also stunt plants but this is usually accompanied by chlorosis or necrosis of the foliage. Venting greenhouses to bring in outside air, providing air circulation to bring the CO2 into contact with the leaf surfaces, or using CO2 injectors will raise levels for optimum plant growth.

Ethylene is a naturally-occurring plant growth regulator produced by senescing plant parts or ripening fruit. It can also result from the incomplete combustion of fuel from a faulty heating system. Symptoms of excess ethylene exposure include the abscission of flower buds, petals or leaves; water-soaking of older leaves; twisting of stems (epinasty); chlorosis; and wilting of flowers. Crops will vary in their sensitivity and response to ethylene toxicity. The degree to which a crop is sensitive depends on the variety, temperature, ethylene concentration, and the duration of exposure. High temperatures and high light levels will increase the severity of ethylene damage. The following table excerpted from the Ball RedBook indicates the response of common greenhouse crops to ethylene.

Plants can also be exposed to excess ethylene in storage or transport. To avoid damage, keep plants cool and provide adequate air circulation. Also, don’t transport plants with fruit as the latter will give off ethylene gas that can injury your crop.

Ozone injury appears as pale flecks on the foliage. It can retard plant growth and make plants more susceptible to pathogenic diseases and insect pests. Ozone is produced when products of combustion react with oxygen. It is also produced by electrical equipment that operates at high voltages.

Sulfur dioxide (SO₂) occurs when heaters or CO₂ generators malfunction or when fuels with high sulfur contents, such as coal, oil or natural gas are burned. The gas enters the plant through the stomata or it may mix with water to produce a sulfuric acid that can burn the plants. Acute SO₂ injury presents as marginal or interveinal necrosis or as a bleaching of the affected tissue.

You can prevent greenhouse gas problems by making sure all equipment and heaters are in proper working condition and by ventilating the greenhouse. Where this is not possible, consider growing those plant species that are more tolerant of air pollutants in areas with poor air quality.