Abstract
Elevated tropospheric ozone concentration (O(3) ) significantly reduces photosynthesis and productivity in several C(4) crops including maize, switchgrass and sugarcane. However, it is unknown how O(3) affects plant growth, development and productivity in sorghum (Sorghum bicolor L.), an emerging C(4) bioenergy crop. Here, we investigated the effects of elevated O(3) 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 O(3) 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 O(3) . At the FACE experiment, elevated O(3) did not alter net CO(2) 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 O(3) and could be used to enhance biomass productivity in O(3) polluted regions.