Interactive Effects of Elevated CO₂ and Growth Temperature on the Tolerance of Photosynthesis to Acute Heat Stress in C₃ and C₄ Species

• Published in: Journal of integrative plant biology 2008-11, Vol.50 (11), p.1375-1387
• Main Authors: Hamilton III, E. William, Heckathorn, Scott A, Joshi, Puneet, Wang, Dan, Barua, Deepak
• Format: Article
• Language: English
• Subjects: Amaranthus - drug effects; Amaranthus - physiology; carbon dioxide; Carbon Dioxide - toxicity; Chenopodium album - drug effects; Chenopodium album - physiology; climate change; Electron Transport - drug effects; global climate change; heat tolerance; photosynthesis; Photosynthesis - drug effects; Photosynthesis - physiology; Pisum sativum - drug effects; Pisum sativum - physiology; Plant Transpiration - drug effects; Plants - drug effects; Plants - metabolism; Temperature; thermotolerance; Zea mays - drug effects; Zea mays - physiology
• ISSN: 1672-9072; 1744-7909
• DOI: 10.1111/j.1744-7909.2008.00747.x

Determining effects of elevated CO₂ on the tolerance of photosynthesis to acute heat-stress (heat wave) is necessary for predicting plant responses to global warming, as photosynthesis is thermolabile and acute heat-stress and atmospheric CO₂ will increase in the future. Few studies have examined this, and past results are variable, which may be due to methodological variation. To address this, we grew two C₃ and two C₄ species at current or elevated CO₂ and three different growth temperatures (GT). We assessed photosynthetic thermotolerance in both unacclimated (basal tolerance) and pre-heat-stressed (preHS = acclimated) plants. In C₃ species, basal thermotolerance of net photosynthesis (Pn) was increased in high CO₂, but in C₄ species, Pn thermotlerance was decreased by high CO₂ (except Zea mays at low GT); CO₂ effects in preHS plants were mostly small or absent, though high CO₂ was detrimental in one C₃ and one C₄ species at warmer GT. Though high CO₂ generally decreased stomatal conductance, decreases in Pn during heat stress were mostly due to non-stomatal effects. Photosystem II (PSII) efficiency was often decreased by high CO₂ during heat stress, especially at high GT; CO₂ effects on post-PSII electron transport were variable. Thus, high CO₂ often affected photosynthetic theromotolerance, and the effects varied with photosynthetic pathway, growth temperature, and acclimation state. Most importantly, in heat-stressed plants at normal or warmer growth temperatures, high CO₂ may often decrease, or not benefit as expected, tolerance of photosynthesis to acute heat stress. Therefore, interactive effects of elevated CO₂ and warmer growth temperatures on acute heat tolerance may contribute to future changes in plant productivity, distribution, and diversity.