Crop responses to elevated CO2 and interactions with H2O, N, and temperature

About twenty-seven years ago, free-air CO2 enrichment (FACE) technology was developed that enabled the air above open-field plots to be enriched with CO2 for entire growing seasons. Since then, FACE experiments have been conducted on cotton, wheat, ryegrass, clover, potato, grape, rice, barley, sugar beet, soybean, cassava, rape, mustard, coffee (C3 crops), and sorghum and maize (C4 crops). Elevated CO2 (550 ppm from an ambient concentration of about 353 ppm in 1990) decreased evapotranspiration about 10% on average and increased canopy temperatures about 0.7 °C. Biomass and yield were increased by FACE in all C3 species, but not in C4 species except when water was limiting. Yields of C3 grain crops were increased on average about 19%.