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item Ziska, Lewis

Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Plant photosynthesis will be stimulated as atmospheric carbon dioxide increases. The degree of photosynthetic stimulation and plant growth should be enhanced at higher temperatures based on what is known about the biochemistry of photosynthesis. However, recent studies have shown that the stimulation of photosynthesis at future, elevated concentrations of atmospheric carbon dioxide is not always observed, even if temperatures rise simultaneously. Under these conditions, stimulation of photosynthesis with increased carbon dioxide is less than expected with rising temperature. This result is in conflict with most global models which predict the impact of rising carbon dioxide and temperature on agricultural productivity. To determine the basis for discrepancies from the models, velvetleaf, a summer annual weed was used as a test species. Data from this experiment showed that existing models can be modified with more realistic parameters so that they agree with the experimental data. By doing so, more likely scenarios of global climate change and agriculture can be generated. Such scenarios are crucial in assessing the impact of climate change on U.S. and global agricultural productivity.

Technical Abstract: Based on the temperature-dependent carboxylation kinetics of ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco), the short-term stimulation of photosynthesis in response to elevated carbon dioxide concentration [CO2], should be highly temperature dependent at high photon flux. In climate controlled studies of velveltleaf (Albutilon theophrasti) the response of photosynthesis, determined as CO2 assimilation was measured over a range of internal CO2 concentrations at seven measurement (12, 16, 20, 24, 28, 32, 36oC) temperatures for each of four growth (16, 20, 28 and 32oC) temperatures. In vivo estimates of Rubisco carboxylation velocity and maximum electron flow were determined from gas exchange measurements for each temperature combination. The temperature dependence of photosynthetic enhancement for Albutilon theophrasti at elevated carbon dioxide was a function of the growth temperature. This was due, in part to changes in the optimal temperature of in vivo Rubisco activity and electron flow. Models which assumed no growth temperature effect on carboxylation kinetics or no limitation by electron flow over predicted the temperature dependence of the photosynthetic response to elevated carbon dioxide at temperatures above 24oC. Overall, previous exposure to a given growth temperature appeared to alter the response of electron flow and Rubisco carboxylation velocity to short-term increases in temperature and this needs to be taken into account in modeling the temperature dependence of photosynthetic stimulation at elevated carbon dioxide.