Ozone (O 3 ) in the troposphere negatively impacts crop growth and development, causing significant decreases in crop yield worldwide. This airborne pollutant does not come directly from smokestacks or vehicles, but instead is formed when other pollutants, mainly nitrogen oxides and volatile organic compounds, react in the presence of sunlight. In an increasingly polluted atmosphere, understanding what plants are tolerant of O 3 is critical to improving crop productivity and resilience.
In a collaboration between the Feedstock Production and Sustainability themes at the Center for Advanced Bioenergy and Bioproducts Innovation (CABBI), researchers have studied the effects of elevated O 3 on five C 3 crops (chickpea, rice, snap bean, soybean, wheat) and four C 4 crops (sorghum, maize, Miscanthus × giganteus , switchgrass). Their findings, published in Proceedings of the National Academy of Sciences ( PNAS ) , indicate that C 4 crops are much more tolerant of high O 3 concentrations than C 3 crops.
“Understanding the tolerance of C 4 bioenergy crops to air pollutants will help us deploy them strategically across landscapes around the world,” said Lisa Ainsworth, Research Leader of the U.S. Department of Agriculture Agricultural Research Service's (USDA-ARS) Global Change and Photosynthesis Research Unit and Adjunct Professor of Plant Biology at the University of Illinois.
Both C 3 and C 4 crops are major sources of food, bioenergy, and ethanol production worldwide. The difference between C 3 and C 4 plants lies in the carbon-fixation pathway they use during photosynthesis: C 3 plants convert CO 2 and sunlight into a 3-carbon molecule, whereas the first photosynthesis product of C 4 plants is a 4-carbon molecule. Additionally, the C 4 photosynthesis pathway starts in mesophyll cells that comprise the surface of the leaf, and then moves into bundle sheath cells that are deeper in the plant. This spatial separation is not present in the C 3 photosynthesis pathway. Scientists have historically assumed that C 4 plants are less sensitive to O 3 pollution than C 3 plants, but that assumption had not been thoroughly researched until this study.
“Variation in size and growing season length means that it is difficult to do side-by-side comparisons of the response of C 3 and C 4 crops to ozone in the field” said Shuai Li, primary author on the paper and a postdoc in CABBI. “This limits accurate comparisons of the O 3 sensitivity of C 3 and C 4 crops.”
By synthesizing available literature and unpublished data from crops grown with increased O 3 pollution in open-air field experiments over the past 20 years, authors performed a comprehensive analysis of the impact of O 3 on crop physiology and production in five C 3 crops and four C 4 crops.
“We focused on field experiments and quantified crop responses to a specific increase in O 3 pollution. This new method quantitatively showed that C 3 crops are more sensitive to elevated ozone than C 4 crops,” Li said.
The reasoning behind such a conclusion could to do with the differences in leaf anatomical features, stomatal conductance, and/or metabolic rates between the C 3 and C 4 crops. In C 3 plants, reactive oxygen species from O 3 degradation can damage the mesophyll cells where photosynthesis occurs. In C 4 plants, however, the spatial separation of the C 4 photosynthesis pathway helps prevent O 3 from infiltrating the bundle sheath cells where sugars are made. In addition, C 4 crops generally have lower stomatal conductance than C 3 crops, potentially resulting in less O 3 uptake in C 4 crops. These factors likely account for C 4 plants’ superior tolerance of O 3 .
“This study enhances our understanding of the mechanisms of crops response to elevated O 3 and highlights practical relevance for crop management and O 3 tolerance improvement.” Li said.
Ozone pollution is increasing in many parts of the world. This study quantitatively showed that O 3 -induced reductions in plant function and productivity are more severe in C 3 crops than in C 4 crops, likely because O 3 interacts differently with the C 3 and C 4 photosynthesis pathways. Based on this finding, agricultural lands in polluted environments can be managed to have improved overall performance. C 4 crops, particularly bioenergy feedstocks, can maintain productivity in regions with high O 3 .
Other co-authors on this paper include Christopher Moller of the Carl R. Woese Institute for Genomic Biology (IGB) at Illinois and USDA-ARS; Christopher Montes, USDA-ARS Plant Physiologist; Erik Sacks, Professor of Crop Sciences at Illinois and CABBI’s Feedstock Production Deputy Theme Leader; DoKyoung Lee, Professor of Crop Sciences at Illinois and a CABBI Sustainability researcher; and CABBI Director Andrew Leakey, Professor and Head of Plant Biology at the Illinois.
Read the full research manuscript in PNAS >>>
— Article by CABBI Communications Specialist April Wendling
Proceedings of the National Academy of Sciences
Experimental study
Not applicable
“Similar Photosynthetic but Different Yield Responses of C3 and C4 Crops to Elevated O3.”
10-Nov-2023