It is well established that chronic exposure to high levels of ozone is a serious threat to human health, exacerbating heart and lung problems such as asthma and emphysema and causing weight loss at birth. One study found that more than 1 million premature deaths are caused worldwide by high levels of ozone each year.
Studies also show that crops and forests are damaged or killed by ozone, directly or indirectly, as ozone makes them more susceptible to insects, disease and drought. According to the US Department of Agriculture, ozone causes more damage to plants than all other air pollutants combined. Gas is expected to cause a significant drop in world food production. A recent study predicts that by 2050, wheat yields will fall by 13%, soybeans by 28% and corn by 43% due to rising temperatures and ozone.
Although it is clear that ozone can affect all living organisms, until recently research has not looked at its effect on biodiversity. However, scientists believe that the impact is significant. This month, the International Union of Forest Research Organizations, a global network of scientists, is holding a conference entitled “Air Pollution from Threats to Plant Ecosystems.” Ozone is at the top of the list.
In a report published last year, 20 researchers in Europe and Asia, including Agathakleous, modeled what could happen to ecosystems in the coming decades as a result of ozone pollution. They concluded that ozone would affect “the composition and diversity of plant communities by affecting basic physiological traits” and could cause a cascade of changes that reduce biodiversity. In their report, the researchers called on officials to take ozone into account in efforts to conserve and restore biodiversity and said its effects should be included in assessments of air pollution and climate change.
Studies show that ozone affects plants in a variety of ways.
“This paralyzes the stomata of plants,” says Howard Neufeld, a plant ecologist at Appalachian State University, “and so they release more water than they absorb.” The stomata are the microscopic openings on the surface of the leaves where the trees exchange gases with the atmosphere. Ozone damages them and interferes with various processes, including photosynthesis.
Ozone also damages the leaves and accelerates their aging. “When the leaves are injured, photosynthesis decreases; a plant produces less sugar and has fewer resources, ”says Neufeld. “It also affects the movement of sugars to the roots, which reduces root growth, making them more susceptible to drought and nutrient and disease deficiencies.”
Ozone depletion can also change the time of leaf fall and reduce leaf size, reducing the amount of waste and affecting microbial communities that thrive on leaf decomposition. Microbes in waste and soil are crucial for the absorption of nutrients, helping trees to resist disease and use water efficiently.
The impact of ozone on the soil also affects the rhizosphere – the root system and related microbes, fungi and other organisms. “When plants react to ozone, they consume energy,” says Agathocleus. “When they use so much energy, there is less to provide for the organisms in the soil and the chemical composition can be affected.” Fewer food leaves can also affect the life cycle of the animals that feed on them.