Ozone and plants
Carbon dioxide is used by plants for photosynthesis, allowing them to grow and reproduce. However, when plants take up carbon dioxide, they also take up all of the other components of the atmosphere including pollutants like ozone. We normally think of ozone as a protective atmospheric layer, far above us, but when it occurs closer to Earth’s surface, among the air we breathe, it is actually a pollutant . Ozone pollution is formed in the atmosphere when chemicals released from cars, power plants, and refineries react with sunlight.
When plants take up ozone it forms dangerous compounds in the plant’s tissue. Getting rid of these harmful compounds requires the plant to use a lot of energy that would usually go towards growth and reproduction, but is now being diverted to cope with dangerous compounds. This results in lower growth rates, reproductive outputs, and crop yields.
Global wheat production
Wheat currently provides 20% of dietary protein and caloric intake for the worlds growing population. According to the United Nations, the current global population is 7.6 billion people and is projected to reach almost 10 million by 2050. To provide this growing population with proper nutrition, we need to increase the global production of important crops, including wheat.
In 2014, the International Wheat Yield Partnership was formed with the goal of enhancing global wheat production by 50% in 20 years, primarily through breeding programs that aim to increase how efficiently wheat plant’s can photosynthesize. Other strategies for increasing production include increasing crop irrigation and optimizing crop fertilization.
Ozone and wheat production
The negative effects of ozone on wheat production have traditionally been estimated based on dose-response relationships and the atmospheric concentration of ozone. This approach is problematic because it does not take into account the rate at which plants are taking up ozone in different environments; these rates differ considerably between dry and humid regions of the globe.
To better determine what impact ozone has on world wheat production, Gina Mills from the Centre for Ecology and Hydrology (Bangor, UK) and colleagues from across the globe recently published a study that accounted for the rate of ozone uptake by wheat in different environments and predicted the effects of ozone on wheat production.
Their model showed that from 2010-2012 ozone reduced wheat yield by an average of 9.9% in the northern hemisphere and 6.2% in the southern hemisphere, resulting in a loss of 85 million tons of wheat, which was valued at $24.4 billion dollars per year. Interestingly, developing countries had 50% higher reductions in wheat yield than developed countries. Demand for wheat in developing countries is increasing nearly twice as fast as in developed countries, making the negative effect of ozone on wheat production in these areas even more significant.
Importantly, Mills and her colleagues showed that increasing irrigation in certain regions also increased the accumulation of ozone by plants. This means the negative effects of ozone could counteract the positive benefits of irrigation in some cases. Overall, the greatest losses in wheat yields were in warm, moist areas such as regions of China, India, the United States, which are three of the top wheat producing countries. If you are interested in visualizing the results, I encourage you to look at Figure 1 of the study that shows the negative effects of ozone based on three different models that were tested. The article is available free of charge to everyone, just click on the hyperlink above.
Conclusions and future directions
The results of Mills et al. have important implications for global wheat production and for efforts to increase production in the coming years. Breeding programs, such as the one lead by the International Wheat Yield Partnership could select for strains that are resistant to ozone pollution, which may be especially beneficial for developing countries. But the ultimate solution to the problem of ozone pollution is to decrease the amount of air pollutants that we are releasing into the atmosphere from our cars and power plants, which eventually become ozone. Investing in clean energy solutions and strategies to reduce or mitigate the effects of ozone pollution should be a top priority for scientists, governments, and citizens alike. Conserving energy, carpooling, and ensuring proper maintenance of your cars can help lower the amount of air pollution you are creating. To learn about other actions you can take to reduce air pollution, check out these suggestions from the US EPA.
Mills G, Sharps K, Simpson D, Pleijel, H, Broberg M, Uddling J, Jaramillo F, Davies WJ, Denetener F, Van den Berg M, Agrawal M, Agrawal SB, Ainsworth EA, Büker P, Emberson L, Feng Z, Harmens H, Hayes D, Kobayashi K, Paoletti E, Van Dingenen R. Ozone pollution will compromise efforts to increase global wheat production. Global Change Biology 2018; 24:3560–3574. https://doi.org/10.1111/gcb.14157