D. R. Taub and X. Wang, “Why Are Nitrogen Concentrations in Plant Tissues Lower under Elevated CO2? A Critical Examination of the Hypotheses,” Journal of Integrative Plant Biology, Vol. 50, No. 11, 2008, pp. 1365-1374.
 S. K. Aben, S. P. Seneweera, O. Ghannoum and J. P. Conroy, “Nitrogen Requirements for Maximum Growth and Photosynthesis of Rice, Oryza sativa L. cv. Jarrah Grown at 36 and 70 Pa CO2,” Australian Journal of Plant Physiology, Vol. 26, No. 8, 1999, pp. 759-766.
 G. S. Rogers, L. Payne, P. Milham and J. Conroy, “Nitrogen and Phosphorus Requirements of Cotton and Wheat under Changing Atmospheric CO2 Concentrations,” Plant and Soil, Vol. 155-156, No. 1, 1993, pp. 231-234.
 O. Ghannoum and J. P Conroy, “Nitrogen Deficiency Precludes a Growth Response to CO2 Enrichment in C3 and C4 Panicum Grasses,” Australian Journal of Plant Physiology, Vol. 25, No. 5, 1998, pp. 627-636.
 H. Harmens, C. M. Stirling, C. Marshall and J. F. Farrar, “Does Down-Regulation of Photosynthetic Capacity by Elevated CO2 Depend on N Supply in Dactylis glomerata?” Physiologia Plantarum, Vol. 108, No. 1, 2000, pp. 43-50.
 H. Y. Kim, M. Lieffering, K. Kobayashi, M. Okada, M. W. Mitchell and M. Gumpertz, “Effects of Free-Air CO2 Enrichment and Nitrogen Supply on the Yield of Temperate Paddy Rice Crops,” Field Crops Research, Vol. 83, No. 3, 2003, pp. 261-270.
 L. H. Ziska, W. Weerakoon, O. S. Namuco and R. Pamplona, “The Influence of Nitrogen on the Elevated CO2 Response in Field-Grown Rice,” Australian Journal of Plant Physiology, Vol. 23, No. 1, 1996, pp. 45-52.
 M. Stitt and A. Krapp, “The Interaction between Elevated Carbon Dioxide and Nitrogen Nutrition: The Physiological and Molecular Background,” Plant, Cell and Environment, Vol. 22, No. 6, 1999, pp. 741-621.
 E. P. McDonald, J. E. Erickson and E. L. Kruger., “Can Decreased Transpiration Limit Plant Nitrogen Acquisition in Elevated CO2?” Functional Plant Biology, Vol. 29, No. 9, 2002, pp. 1115-1120.
 H. Shimono and J. A. Bunce, “Acclimation of Nitrogen Uptake Capacity of Rice to Elevated Atmospheric CO2 Concentration,” Annals of Botany, Vol. 103, No. 1, 2009, pp. 87-94. http://dx.doi.org/10.1093/aob/mcn209
 S.-Y. Kim, R. C. Sicher, H. Bae, D. C. Gitz, J. T. Baker, D. J. Timlin and V. R. Reddy, “Canopy Photosynthesis, Evapotranspiration, Leaf Nitrogen, and Transcription Profiles of Maize in Response to CO2 Enrichment,” Global Change Biology, Vol. 12, No. 3, 2006, pp. 588-600. http://dx.doi.org/10.1111/j.1365-2486.2006.01110.x
 A. D. B. Leakey, M. Uribelarrea, E. A. Ainsworth, S. L. Naidu, A. Rogers, D. R. Ort and S. P. Long, “Photosynthesis, Productivity, and Yield of Maize Are Not Affected by Open-Air Elevation of CO2 Concentration in the Absence of Drought,” Plant Physiology, Vol. 140, No. 2, 2006, pp. 779-790.
 P. V. Vara Prassad, K. J. Boote and L. H. Allen Jr., “Adverse High Temperature Effects on Pollen Viability, Seed-Set, Seed Yield and Harvest Index of Grain-Sorghum [Sorghum bicolor (L.) Moech] Are More Severe at Elevated Carbon Dioxide Due to Higher Tissue Temperatures,” Agricultural and Forest Meteorology, Vol. 139, No. 3-4, 2006, pp. 237-251.
 J. A. Bunce, “What Is the Usual Internal Carbon Dioxide Concentration in C4 Species under Midday Field Conditions?” Photosynthetica, Vol. 43, No. 4, 2005, pp. 603-608. http://dx.doi.org/10.1007/s11099-005-0094-y
 R. J. C. Markelz, R. S. Strellner and A. D. B. Leakey, “Impairment of C4 Photosynthesis by Drought Is Exacerbated by Limiting Nitrogen and Ameliorated by Elevated [CO2] in Maize,” Journal of Experimental Botany, Vol. 62, No. 9, 2011, pp. 3235-3246.
 R. Manderscheid, M. Erbs and H.-J. Weigel, “Interactive Effects of Free-Air CO2 Enrichment and Drought Stress on Maize Growth,” European Journal of Agronomy, Vol. 43, 2012, pp. 97-107.
 D. J. Watson, “The Physiological Basis of Variation in Yield,” Advances in Agronomy, Vol. 4, 1952, pp. 101-145.
 H. H. Rogers, G. E. Bingham, J. D. Cure, J. M. Smith and K. A. Surano, “Responses of Selected Plant Species to Elevated Carbon Dioxide in the Field,” Journal of Environmental Quality, Vol. 12, No. 4, 1983, pp. 569-574.
 A. D. B. Leaky, C. J. Bernacchi, F. G. Dohleman, D. R. Ort and S. P. Long, “Will Photosynthesis of Maize (Zea mays) in the US Corn Belt Increase in Future [CO2] Rich Atmosphere? An Analysis of Diurnal Courses of CO2 Uptake under Free-Air Concentration Enrichment (FACE),” Global Change Biology, Vol. 10, No. 6, 2004, pp. 951-962. http://dx.doi.org/10.1111/j.1529-8817.2003.00767.x
 J. S. Boyer, “Leaf Enlargement and Metabolic Rates in Corn, Soybean, and Sunflower at Various Leaf Water Potentials,” Plant Physiology, Vol. 46, No. 2, 1970, pp. 233-235. http://dx.doi.org/10.1104/pp.46.2.233
 Y. Assefa, K. L. Roozenboom, S. A. Staggenborg and J. Du, “Dryland and Irrigated Corn Yield with Climate, Management, and Hybrid Changes from 1939 through 2009,” Agronomy Journal, Vol. 104, No. 2, 2012, pp. 473-482. http://dx.doi.org/10.2134/agronj2011.0242
 E. P. Wilhelm, R. E. Mullen, P. L. Keeling and G. W. Singletary, “Heat Stress during Grain Filling in Maize: Effect on Kernel Growth and Metabolism,” Crop Science, Vol. 39, No. 6, 1999, pp. 1733-1741.
 USDA Economics, “Statistics and Market Information System,” 2013.