Elevated Ozone Concentration Reduces Photosynthetic Carbon Gain but Does Not Alter Leaf Structural Traits, Nutrient Composition or Biomass in Switchgrass.

Elevated tropospheric ozone concentration (O₃) increases oxidative stress in vegetation and threatens the stability of crop production. Current O₃ pollution in the United States is estimated to decrease the yields of maize (Zeamays) up to 10%, however, many bioenergy feedstocks including switchgrass (Panicum virgatum) have not been studied for response to O₃ stress. Using Free Air Concentration Enrichment (FACE) technology, we investigated the impacts of elevated O₃ (~100 nmol mol^-1) on leaf photosynthetic traits and capacity, chlorophyll fluorescence, the Ball⁻Woodrow⁻Berry (BWB) relationship, respiration, leaf structure, biomass and nutrient composition of switchgrass. Elevated O₃ concentration reduced net CO₂ assimilation rate (A), stomatal conductance (g_s), and maximum CO₂ saturated photosynthetic capacity (V_max), but did not affect other functional and structural traits in switchgrass or the macro- (except potassium) and micronutrient content of leaves. These results suggest that switchgrass exhibits a greater O₃ tolerance than maize, and provide important fundamental data for evaluating the yield stability of a bioenergy feedstock crop and for exploring O₃ sensitivity among bioenergy feedstocks.