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Title:   Author  item
                                            BISHOP, K - University Of Illinoisitem
                                            LEAKEY, ANDREW D B - University Of Illinoisitem
                                            Ainsworth, Elizabeth

                                                         - *Lisa*
  Submitted to: Food and Energy Security
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 4/29/2014
                                    Publication  Date: 5/29/2014
                                    Citation: Bishop, K.A., Leakey, A., Ainsworth, E.A. 2014. How seasonal temperature or water inputs affect the relative response of C3 crops to elevated [CO2]: A global analysis of open top chamber and Free Air CO2 Enrichment (FACE) studies. Food and Energy Security. DOI: 10.1002/fes3.44.Interpretive Summary: A large number of experiments have investigated crop responses to rising atmospheric carbon dioxide concentrations using open top chambers or completely open-air free air CO2 enrichment (FACE) facilities. These experiments with plants rooted in the ground give us our best estimation of how crops will respond to the changes in atmospheric CO2 anticipated for later this century.  While crop photosynthesis and yield is generally stimulated by growth at elevated CO2, the magnitude of the stimulation can vary with genetic differences among and between crops as well as with environmental conditions. In this meta-analysis, we examined the relationship between growing season temperature and water input and the relative yield response of crops to elevated CO2. We found that counter to our prediction that CO2 response would be greater at higher temperatures, growing season average temperature was not a good predictor of the magnitude of biomass and yield responses to elevated [CO2]. On the other hand, the relative stimulation of yield by elevated [CO2] was greatest in drier conditions, as predicted. Our results show that environmental variation can have a large effect on crop respones to elevated [CO2] and for crop models, one simple CO2 fertilization value is not appropriate for accurately predicting crop productivity under future environmental conditions.
                                Technical Abstract: Rising atmospheric carbon dioxide concentration ([CO2]) has the potential to positively impact C3 food crop production by directly stimulating photosynthetic carbon gain (A), which feeds forward to increase crop biomass and yield. Further stimulation of A and yield can result from an indirect mechanism in which elevated [CO2] causes reductions in stomatal conductance and canopy water use, ameliorating drought stress. Field-grown experiments in open top chambers (OTC) and free air CO2 enrichment (FACE) facilities have enabled investigation of crop responses to elevated [CO2] in near natural, field conditions. These experiments report average increases in crop yield of 27% in OTC experiments and 19% in FACE experiments. Mechanistic understanding of physiological responses to elevated [CO2] has led to prediction that the stimulation of A, biomass production and economic yield will vary with the temperature and water supply experienced by the crop. This study tested current assumptions about the relationships between relative responses of yield and biomass to elevated [CO2] and variation in growing season temperature and water inputs (precipitation plus irrigation). Growing season average temperature was not a good predictor of the magnitude of biomass and yield responses to elevated [CO2], contradicting the prediction that response to [CO2] would increase with increasing temperature due to the greater benefit from decreasing photorespiration.  However, the prediction that the relative stimulation of yield by elevated [CO2] would be greatest in drier conditions was supported. Thus, a simple CO2 fertilization value is not appropriate for modeling future crop productivity under varying environmental conditions. Further studies are necessary across a broader range of environmental conditions in order to assess near-term responses in high and low latitudes, as well as temperate crop responses in the temperate zone under future, altered climates.


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