Submitted to: Plant Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/20/2014
Publication Date: 9/1/2014
Citation: Bunce, J.A. 2014. Limitations to soybean photosynthesis at elevated carbon dioxide in free-air enrichment and open top chamber systems. Plant Science. 226:131-135. Interpretive Summary: The stimulation in crop yields with rising atmospheric carbon dioxide depends primarily on the amount of increase in photosynthesis. The amount of stimulation in photosynthesis at elevated carbon dioxide depends on which biochemical component of the photosynthetic system limits photosynthesis. These experiments tested which component was limiting in soybeans grown under field conditions at an elevated carbon dioxide concentration using two different carbon dioxide enrichment systems. The results will be of interest to scientists attempting to maximize crop yields at future atmospheric carbon dioxide concentrations.
Technical Abstract: It has been suggested that the stimulation of soybean photosynthesis by elevated carbon dioxide concentration was less in free-air carbon dioxide enrichment (FACE) systems than in open top chambers (OTC). However, this has not been tested using the same cultivars grown in the same location. We tested the hypothesis that soybean photosynthesis at high light and elevated carbon dioxide (ambient + 180 ppm) was limited by electron transport in FACE systems but by ribulose-bisphosphate carboxylation capacity in OTC. We also compared FACE systems with daytime and continuous carbon dioxide enrichment. The results indicated that in both cultivars examined, midday photosynthesis at high light was always limited by ribulose-bisphosphate carboxylation capacity, both in the FACE and in the OTC systems. Daytime only carbon dioxide enrichment did not affect photosynthetic parameters or limitations, but did result in significantly smaller yields in both cultivars than continuous elevation. Photosynthesis measured at low photosynthetic photon flux density was not higher at elevated than at ambient carbon dioxide, because of an acclimation to elevated carbon dioxide which was only evident at low measurement photon flux density. This type of acclimation of photosynthesis to elevated carbon dioxide could substantially reduce daily canopy photosynthesis, and should be accounted for in soybean crop simulation models.