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Title:   Author  item
                                            Kim, Soo Hyungitem
                                            Sicher  Jr, Richarditem
                                            BAE, HANHONG - UNIV OF MDitem
                                            Gitz, Dennisitem
                                            Baker, Jeffreyitem
                                            Timlin, Dennisitem
                                            Reddy, Vangimalla
  Submitted to: Global Change Biology
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 11/4/2005
                                    Publication  Date: 3/17/2006
                                    Citation: Kim, S., Sicher  Jr, R.C., Bae, H., Gitz, D.C., Baker, J.T., Timlin, D.J., Reddy, V. 2006. Canopy photosynthesis, evapotranspiration, leaf nitrogen, and transription profiles of maize in response to co2 enrichment. Global Change Biology. 12:588-600.Interpretive Summary: Future global carbon dioxide concentrations are expected to reach between 540 and 970 parts per million by the end of this century. It is critical to understand how rising carbon dioxide will affect the growth and development of major crop plants. Corn is the number one crop in the United States in terms of total production and cultivated area. We investigated the effects of elevated [CO2] on the growth, development and physiology of corn plants grown from seed to maturity in special sunlit, fully-enclosed chambers. We found that increasing carbon dioxide levels within the chambers did not alter plant growth rates or carbon formation and storage.  However, a reduction in the use both of water and nitrogen was detected.  This was probably due to the fact that carbon dioxide closed pores on the leaves known as stomates.   Expression levels of approximately 160 corn genes were altered by carbon dioxide enrichment. These results suggested that elevated atmospheric carbon dioxide in the future would not alter the growth and development of corn under well watered conditions but under water limited conditions corn may benefit from carbon dioxide enrichment because of reduced water usage. Reduced nitrogen levels in corn tissues in response to elevated carbon dioxide were likely due to decreased water consumption.  This study will allow researchers and policy makers to assess the impacts of future global climate change on corn production in the United States and in the world.
                                Technical Abstract: It is critical to assess the effects of rising atmospheric carbon dioxide concentration ([CO2]) on the growth, development and yield of maize given its overall importance as a crop in global agricultural systems.  We investigated maize plants grown from seed to maturity in sunlit Soil-Plant-Atmosphere-Research (SPAR) chambers at either ambient (370 umol mol-1) or elevated (750 umol mol-1) [CO2].  Shoot biomass, leaf area, leaf and whole-canopy photosynthetic rates, and four C4 enzyme activities did not differ between the ambient and elevated CO2 treatments. Leaf and whole-plant transpiration rates and stomatal conductance decreased, and leaf temperatures measured at the top of the canopy were greater in the elevated compared to the ambient CO2 treatment. Foliar N content decreased in response to CO2 enrichment resulting in increased C/N ratio. The carboxylation efficiency, measured by the initial slope of leaf A/Ci response curve, also was decreased in the elevated compared to the ambient CO2 treatment.  Among 7,442 transcripts tested using maize cDNA microarrays, transcripts for 227 genes increased and160 decreased, in the elevated [CO2] treatment.  Transcripts for cytosolic glyceraldehyde 3-phosphate dehydrogenase, fructose 1,6-bisphosphate aldolase and fructose 1,6-bisphosphatase were repressed by CO2 enrichment, suggesting glycolysis was decreased. Our results support the hypothesis that decreased transpiration rates reduced N fluxes from soil to plant. This might have decreased N assimilation rates and triggered signaling cascades that resulted in altered transcription profiles without concurrent changes in photosynthesis or growth.


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