Crop Responses to Elevated Carbon Dioxide

Atmospheric carbon dioxide (CO2) concentration has increased from 280 ppm (parts per million, mole fraction basis) in preindustrial times to 370 ppm today. As concentrations of CO2 and other greenhouse gases rise, global temperature is anticipated to increase. Elevated CO2 will improve crop yields due to increased photosynthesis. However, at above-optimum temperatures for reproductive growth processes, the benefits of elevated CO2 could be overwhelmed by negative effects of high temperature, leading to lower seed yield. The extent of growth and yield responses of plants to elevated CO2 depends on the photosynthetic pathway. Crops with C3 photosynthesis will respond markedly to increasing CO2 concentrations. Common C3 crops are small grain cereals (wheat, rice, barley, oat, and rye); grain legumes or pulses (soybean, peanut, various beans and peas); root and tuber crops (potato, cassava, sweet potato, sugar beet, yams); most oil, fruit, nut, vegetable, and fiber crops; and temperate-zone (cool-climate) forage and grassland species. In contrast, plants with C4 photosynthesis will respond little to rising atmospheric CO2 because a mechanism to increase the concentration of CO2 in leaves causes CO2 saturation of photosynthesis at current ambient concentrations. Common C4 crops are maize (corn), sugarcane, sorghum, millet, and many tropical and subtropical zone (warm-climate) grass species. This article focuses on responses to elevated CO2 and increased temperature of C3 crops. Response patterns are similar, but not the same, across a broad range of species and conditions.