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Interactive Effects of Elevated CO₂ and Ozone on Leaf Thermotolerance in Field-grown Glycine max

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Humans are increasing atmospheric CO₂, ground-level ozone (O₃), and mean and acute high temperatures. Laboratory studies show that elevated CO₂ can increase thermotolerance of photosynthesis in C₃ plants. O₃-related oxidative stress may offset benefits of elevated CO₂ during heat-waves. We determined effects of elevated CO₂ and O₃ on leaf thermotolerance of field-grown Glycine max (soybean, C₃). Photosynthetic electron transport (Φet) was measured in attached leaves heated in situ and detached leaves heated under ambient CO₂ and O₃. Heating decreased Φet, which O₃ exacerbated. Elevated CO₂ prevented O₃-related decreases during heating, but only increased Φet under ambient O₃ in the field. Heating decreased chlorophyll and carotenoids, especially under elevated CO₂. Neither CO₂ nor O₃ affected heat-shock proteins. Heating increased catalase (except in high O₃) and Cu/Zn-superoxide dismutase (SOD), but not Mn-SOD; CO₂ and O₃ decreased catalase but neither SOD. Soluble carbohydrates were unaffected by heating, but increased in elevated CO₂. Thus, protection of photosynthesis during heat stress by elevated CO₂ occurs in field-grown soybean under ambient O₃, as in the lab, and high CO₂ limits heat damage under elevated O₃, but this protection is likely from decreased photorespiration and stomatal conductance rather than production of heat-stress adaptations.
Mishra, Sasmita , Heckathorn, Scott A. , Barua, Deepak , Wang, Dan , Joshi, Puneet , Hamilton, E. William III , Frantz, Jonathan
Includes references
Journal of integrative plant biology 2008 Nov., v. 50, no. 11
Blackwell Publishing Asia
Journal Articles, USDA Authors, Peer-Reviewed
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