Bioenergy sorghum maintains photosynthetic capacity in elevated ozone concentrations

Elevated tropospheric ozone concentration (O₃ ) significantly reduces photosynthesis and productivity in several C₄ crops including maize, switchgrass and sugarcane. However, it is unknown how O₃ affects plant growth, development and productivity in sorghum (Sorghum bicolor L.), an emerging C₄ bioenergy crop. Here, we investigated the effects of elevated O₃ on photosynthesis, biomass and nutrient composition of a number of sorghum genotypes over two seasons in the field using free-air concentration enrichment (FACE), and in growth chambers. We also tested if elevated O₃ altered the relationship between stomatal conductance and environmental conditions using two common stomatal conductance models. Sorghum genotypes showed significant variability in plant functional traits, including photosynthetic capacity, leaf N content and specific leaf area, but responded similarly to O₃ . At the FACE experiment, elevated O₃ did not alter net CO₂ assimilation (A), stomatal conductance (g_s ), stomatal sensitivity to the environment, chlorophyll fluorescence and plant biomass, but led to reductions in the maximum carboxylation capacity of phosphoenolpyruvate and increased stomatal limitation to A in both years. These findings suggest that bioenergy sorghum is tolerant to O₃ and could be used to enhance biomass productivity in O₃ polluted regions.