Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 18, 1996
Publication Date: N/A
Interpretive Summary: Atmospheric carbon dioxide (CO2) concentration is rising. One predicted consequence is that rainfall patterns may change. Much of the world's irrigated and rainfed rice yields might be decreased if drought becomes more prevalent. Scientists in the Crop Genetic and Environmental Research Unit at Gainesville, FL conducted an experiment in paddy culture rice in which water was withheld and drought imposed at critical stages of growth: (1) at the time that the seed heads were just beginning to initiate in the stems; (2) at the time of flowering, and (3) at both stages of growth. Photosynthesis and water use were decreased only when drought became severe; at that point the plants were rewatered. Overall, CO2 enrichment provided an increase of about 25% in photosynthesis and a decrease of about 10% in water use. This decrease in water use under CO2 enrichment will extend the period of time that plants can extract soil water by about 10%, and will decrease the severity of drought slightly.
Future increases in atmospheric carbon dioxide (CO2) are likely to cause changes in precipitation. Drought is common in global rainfed rice production systems. The objectives were to quantify the effects of CO2 and drought on rice canopy photosynthesis (PS), evapotranspiration (ET), and water-use efficiency (WUE). Rice (cv. IR-72) was grown in eight naturally-sunlit chambers in CO2 concentrations of 350 and 700 micromole CO2 per mole air (ppm). Water management treatments were: continuously flooded controls, flood water removed and drought imposed at panicle initiation, anthesis, and both panicle initiation and anthesis. Potential acclimation of rice PS to long-term CO2 treatments of 350 and 700 ppm was tested by comparing PS rates across short-term CO2 exposure ranging from 160 to 1000 ppm. These tests showed no acclimation with PS being a function of current CO2 rather than long-term CO2 treatment. The CO2 enrichment significantly increased both PS (21 to 27%) and WUE while reducing ET by about 10%. This water savings under CO2 enrichment allowed PS to continue 1 to 2 days longer in enriched compared with ambient CO2.