Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 29, 2008
Publication Date: January 7, 2009
Citation: Vu, J.C., Allen Jr, L.H. 2009. Growth at elevated CO2 delays the adverse effects of drought stress on leaf photosynthesis of the C4 sugarcane. Journal of Plant Physiology. 166:107-116. Interpretive Summary: Atmospheric carbon dioxide (CO2) is expected to double within this century. Research on rising CO2 and consequent climate changes has focused mainly on C3 crops such as soybean and rice. Few tests, however, have been done on C4 crops such as maize and sugarcane. In this study, by ARS scientists with the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL, sugarcane was grown at ambient and double-ambient CO2 for 4 months, and drought was imposed for 13 days. Photosynthesis and sugars were measured in leaves during the drought period to characterize photosynthesis of sugarcane in response to high CO2, and to test if high CO2 could delay the adverse effects of drought on sugarcane photosynthesis. The results showed that high CO2 caused some enhancement in photosynthesis and acclimation in the photosynthetic proteins. High-CO2 plants also transpired less and used water more efficiently than ambient-CO2 plants under both well-watered and drought conditions. In addition, glucose and fructose were much greater for both CO2 stress plants, implying an adaptation of sugarcane to drought. The more efficient use of water at high CO2 allowed the sugarcane stress plants to continue their photosynthesis for at least an extra day during a drought period.
Technical Abstract: Sugarcane was grown in sunlit greenhouses at 360 and 720 ppm CO2, and drought was imposed for 13 days on 4-month old plants. Leaf CO2 exchange rate (CER) and activity of Rubisco were marginally affected by high CO2 but were reduced by drought, whereas activity of PEP carboxylase was reduced by high CO2 but not by drought. In contrast, activities of malate dehydrogenase, malic enzyme and pyruvate Pi dikinase were substantially reduced by drought, but only to a less extent by high CO2. Despite the marginal effect of high CO2 on CER, well-watered plants at high CO2 were lower in leaf conductance (C) and transpiration (T), but greater in leaf water-use efficiency (WUE), than their ambient-CO2 counterparts. High-CO2 plants were also able to maintain higher WUE than ambient-CO2 plants under drought. For well-watered plants, high CO2 did not enhance midday levels of starch or soluble sugars, and severe drought did not affect midday sucrose but greatly reduced starch and substantially increased glucose and fructose in both CO2 treatments. The reductions in C and T and enhancement in WUE in the high-CO2 plants helped to delay the adverse effects of drought, and allowed stress plants to continue photosynthesis for at least an extra day during drought.