Elevated CO2 increases sorghum biomass under drought conditions

Summary •  Atmospheric CO2 concentration is expected to increase by 50% near the middle of this century. The effects the free air CO2 enrichment (FACE) is presented here on growth and development of field-grown grain sorghum (Sorghum bicolor) at ample (wet) and limiting (dry) levels of irrigation water at Maricopa, AZ, USA. •  Daytime CO2 mole fractions were 561 and 368 µmol mol−1 for the FACE and control treatments, respectively. Irrigation plus precipitation averaged 1132 mm for the wet plots and 396 mm in the dry plots. •  During the growing season, FACE increased biomass accumulation in the dry plots but the effects in the wet plots were inconsistent. At final harvest, FACE increased total yield from 999 to 1151 g m−2 in the dry plots and had no effect in the wet plots. •  If atmospheric CO2 continues to increase, total sorghum yield is likely to be higher in the future in areas where water is limited.