Effect of free-air CO2 enrichment on the storage of carbohydrate fixed at different stages in rice (Oryza sativa L.)

Increasing global atmospheric CO2 concentrations are expected to influence crop production. To investigate the effect on rice (Oryza sativa L.), plants were grown under ambient CO2 (AMB) or free-air CO2-erifichment (FACE) at CO2 concentrations ranged from 275 to 365 mu mol mol(-1) above AMB. We supplied (CO2)-C-13 to the plants at different growth stages so we could examine the contribution of carbohydrate stored during the vegetative stage or newly fixed carbohydrate produced during the grain-filling stage to ear weight at grain maturity. In plants supplied with C-13 at the panicle-initiation or pre-heading stages, plants grown under FACE had more starch in the stems at heading, but there was no difference in stem C-13 content. Furthermore, there were no differences between treatments in whole-plant C-13 contents at heading and grain maturity. In contrast, plants supplied with C-13 at the grain-filling stage had more C-13 in the whole plant and the ears at grain maturity under FACE than under AMB, indicating that the increased amount of photosynthate produced at the grain-filling stage under CO2 enrichment might be effectively stored in the grains. Furthermore, regardless of when the C-13 was supplied, plants had more C-13 in starch in the ears at grain maturity under FACE than under AMB. Therefore, CO2 enrichment appears to promote partitioning of photosynthate produced during both vegetative and grain-filling stages to the grains. (c) 2006 Elsevier B.V. All rights reserved.