Tamires S Martins1, Matheus D Laira1, Rafael L Almeida1, Gabriel S Pires1, Dany Afif2, Mireille Cabané2, Anthony Gandin2 and Rafael V Ribeiro1
1Laboratory of Crop Physiology, Department of Plant Biology, Institute of Biology, State University of Campinas (UNICAMP), Campinas, SP, Brazil; tamires0martins@gmail.com
2UMR Silva, AgroParisTech, INRAE, University of Lorraine, Nancy, France
Ozone (O3) is a toxic air pollutant that impairs plant growth, and its effects on C4 species remain underexplored. We investigated the impact of O3 on leaf gas exchange in energy cane and sugarcane. As energy cane is more resilient to environmental stresses than sugarcane, we hypothesized that energy cane would be more tolerant to O3 than would sugarcane. Both sugarcane and energy cane were exposed to three O3 levels (0, 150 and 300 ppb) for three consecutive days, with daily measurements. After one day of exposure, photosynthesis decreased at 150 and 300 ppb O3 in both clones, but sugarcane performance remained similar at both levels, while energy cane exhibited the lowest rates at 300 ppb O3. From the second day, there was no further decline in photosynthesis sugarcane and energy cane due to O3. After one day of O3 exposure, changes in photosynthesis of both clones were supported by reduced photochemical efficiency (ΦPSII) at 150 ppb O3 and by low stomatal conductance (gs) and low ΦPSII at 300 ppb O3. Significant stomatal closure in sugarcane at 150 ppb O3 was noticed only after three days of exposure. After three days of exposure, the maximum carboxylation rates of Rubisco (Vcmax) and PEPC (Vpmax) were decreased at both 150 and 300 ppb O3, with the lowest values found at the highest O3 level. Energy cane presents similar or higher Vpmax and Vcmax than sugarcane under O3 exposure, which is in accordance with its higher photosynthetic rates. However, energy cane photosynthesis declined by 0.30 mmol m-2 s-1 per each 10-ppb increase (R2 = 0.89, p<0.05), while sugarcane photosynthesis declined by 0.20 mmol m-2 s-1 per each 10-ppb increase (R2 = 0.79, p<0.05). In conclusion, energy cane photosynthesis was more sensitive to increasing O3 than was sugarcane, driven by Vcmax and stomatal closure.