PARENT SESSION
Contributed Oral Session 154: Photosynthesis and Water Relations: Climate Effects
Friday, August 12, 8:00 AM - 11:30 AM, Meeting Room 515 A, Level 5, Palais des congrès de Montréal

Growth at elevated CO₂ affects tolerance of photosynthesis to acute heat stress.

Wang, Dan^*,1, Joshi, Puneet¹, Barua, Deepak¹, Hamilton, E.William², Heckathorn, Scott¹, ¹ Dept. of Earth, Ecological, & Environmental Sciences, University of Toledo, Toledo, OH, USA² Dept. of Biology, Washington & Lee University, Lexington, VA, USA

ABSTRACT- Determining photosynthetic responses to acute heat stress in elevated CO₂ is necessary for predicting plant responses to global warming, as photosynthesis is very thermolabile and acute heat stress will increase in the future. Few studies have examined this, and past results are variable, which we hypothesized is due to comparisons of species not grown at species-specific optimal temperatures. In this study, we grew seven species of plants (heat tolerant & sensitive; C3, C4, & CAM) at species-specific optimal temperatures, and at current (370 ppm) and elevated CO₂ (700 ppm). We then assessed both basal and inducible tolerance of net photosynthesis (PN), electron transport (ET), and photosystem II (PSII) to acute heat stress. In nearly all species, ET and PSII were negatively impacted by growth at elevated CO₂, compared to current CO₂, with variation among species in the extent of effects and at which growth temperatures effects were observed. For PN, C3 species were positively affected, but C4 species were negatively affected, by growth at elevated CO₂. Negative effects of high CO₂ were associated with decreased production of heat-shock proteins- a major cellular adaptation to acute heat stress. These results suggest that stimulatory effects of elevated CO₂ at normal temperatures on photosynthesis and growth may be partly offset by negative effects of elevated CO₂ during acute heat stress. Thus, CO₂ effects on acute heat tolerance may contribute to future changes in the productivity, distribution, and diversity of plants.

Key words: global change, photosynthesis, stress proteins