Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 14, 1998
Publication Date: N/A
Interpretive Summary: The rising global atmospheric carbon dioxide concentration (CO2), presently at 365 parts per million, is expected to double within the next century. Predicted climate changes, including shifts in regional scale rainfall precipitation patterns, could result in decreased soil moisture in some parts of the world. It is well known that high CO2 promotes growth and yield, but drought is detrimental to crops. Few tests, however, have been carried out on the combination of these two environmental factors. In this study, by USDA, ARS scientists in Gainesville, FL, rice was grown at ambient or twice-ambient CO2 under continuously flooded conditions, or drought imposed at the critical stage when the seed head was being formed. The purposes were: (1) to determine the combined effects of high CO2 and drought on the biochemistry and molecular biology of photosynthesis, a process by which green leaves absorb CO2 from the air to make products necessary for plant growth and yield; and (2) to test if high CO2 could alleviate or delay the adverse effects of drought on leaf photosynthetic reactions. The results showed that high CO2 alleviated, and significantly delayed by 1 day, the reductions in leaf photosynthetic capacity caused by severe drought, and that rice grown under high CO2 was better able to tolerate drought situations.
Rice (Oryza sativa L. cv. IR-72) was grown in sunlit chambers at ambient and twice-ambient CO2 under conditions of continuous flooding (control) or drought which was imposed at panicle initiation (stressed), to evaluate the effects of high CO2 and drought on gene expression and photosynthesis. High CO2 and severe drought both reduced rbcS transcript abundance, along with the activity, activation and protein content of Rubisco, but the Km(CO2) was not affected. Leaf and canopy photosynthetic rates were enhanced by high CO2 but reduced by drought. The 24-hour transition from moderate to severe drought caused a rapid decline in the rbcS transcript level of the stressed plants. High CO2, however, alleviated and delayed the adverse effects of severe drought on rbcS transcript abundance and activities of Rubisco, and permitted photosynthesis to continue for an extra day during the drought-stress cycle.