Testing unified theories for ozone response in C4 species

Authors: LI, SHUAI - University Of Illinois; MOLLER, CHRISTOPHER - Oak Ridge Institute For Science And Education (ORISE); MITCHELL, NOAH - Oak Ridge Institute For Science And Education (ORISE); LEE, DOKYOUNG - University Of Illinois; SACKS, ERIK - University Of Illinois; Ainsworth, Elizabeth - Lisa

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2022
Publication Date: 1/28/2022
Citation: Li, S., Moller, C.A., Mitchell, N.G., Lee, D., Sacks, E.J., Ainsworth, E.A. 2022. Testing unified theories for ozone response in C4 species. Global Change Biology. 28(10):3379-3393. https://doi.org/10.1111/gcb.16108.
DOI: https://doi.org/10.1111/gcb.16108

Interpretive Summary: Ozone is a damaging air pollutant formed from nitrogen oxides and other pollutants in the atmosphere. The damaging effect of ozone on crop species like soybean, rice and wheat have been well-studied. However, C4 grasses include our most productive food and biofuel crops, and have not been widely investigated for ozone response. In this study, we tested 22 distinct genetic lines in four different C4 species for ozone response in side-by-side trials in the field. We found that the C4 grasses were more tolerant to ozone than other species. Within C4 grasses, stomatal conductance was the primary determinant of sensitivity to ozone. These findings advance understanding of C4 grass responses to ozone and aid in optimal placement of diverse bioenergy species across a polluted landscape.

Technical Abstract: There is tremendous interspecific variability in O3 sensitivity among C3 species, but variation among C4 species’ responses to O3 stress has been less clearly documented. It is also unclear what factors determine the variation in sensitivity to O3 across species. In this study, we investigated leaf morphological, chemical and photosynthetic response of 22 genotypes of four C4 bioenergy species (switchgrass, sorghum, maize and miscanthus) to elevated O3 in side-by-side field experiments using free-air O3 concentration enrichment (FACE). The C4 species varied largely in leaf morphology, physiology and nutrient composition. Elevated O3 did not alter leaf morphology, nutrient content, stomatal conductance, chlorophyll fluorescence and respiration in most genotypes, but reduced net CO2 assimilation in maize and photosynthetic capacity in sorghum and maize. Species with lower leaf mass per area (LMA) and higher stomatal conductance tended to show greater losses in photosynthetic rate and capacity in elevated O3 compared to species with higher LMA and lower stomatal conductance. Stomatal conductance was the strongest determinant of leaf photosynthetic rate and capacity. The response of both area- and mass-based leaf photosynthetic rate and capacity to elevated O3 were not affected by LMA directly, but negatively influenced by LMA indirectly through stomatal conductance. These results demonstrate that there is significant variation in O3 sensitivity among C4 species with maize and sorghum showing greater sensitivity of photosynthesis to O3 than switchgrass and miscanthus. Interspecific variation in O3 sensitivity was determined by direct effects of stomatal conductance and indirect effects of LMA. This is the first study to provide a test of unifying theories explaining variation in O3 sensitivity in C4 bioenergy grasses. These findings advance understanding of O3 tolerance in C4 grasses and could aid in optimal placement of diverse C4 bioenergy feedstocks across a polluted landscape.