Effect of CO_2 enrichment on carbon metabolism of rice plants

本文研究了CO_2浓度升高对水稻碳代谢的影响。本研究首先利用13C示踪技术研究了大气CO_2浓度升高对水稻光合产物分配和运转的影响。结果表明，在CO_2浓度较高的条件下，光合产物向穗部转移的效率比在常温条件下高。此外，在CO_2增施条件下，抽穗期储存在叶鞘中的淀粉向穗部转移的速度比对照快。这说明CO_2增施促进了碳向库器官（穗）的转移和分配。其次，研究了不同CO_2浓度对水稻叶片光合作用的影响。随着大气CO_2浓度的增加，光合作用和光呼吸所消耗的能量减少。因此，CO_2的富集被认为使更多的过剩能量。然而，由于CO_2富集条件下的植物生长与环境条件下的植物一样，多余的能量可能会被激活的替代系统浪费掉。此外，CO_2浓度升高使CO_2从大气向叶绿体羧化位点的通量增加。

In this study, I examined the effect of CO_2 enrichment on carbon metabolism of rice plants. Firstly, the rice plants grown on the paddy field of Free Air CO_2-enrichment Project were used to investigate the effect of CO_2-enrichment on the distribution and translocation of photosynthate using 13C. As a result, the photosynthate in the plants grown under CO_2-enrichment condition had more effectively shifted to the ear than those under ambient condition. Moreover, in the plants grown under CO_2-enrichment condition the starch stored in leaf sheath at heading stage was shifted into ears more rapidly than in those under ambient condition. These suggested that CO_2-enrichment would promote the translocation and distribution of carbon into sink organ (ears). Secondly, the rice plants were grown under various C0_2 concentrations to examine the effect on leaf photosynthesis. The energy used by photosynthesis and photorespiration decreased with the increasing in atmospheric CO_2 concentrations. Therefore, the C0_2 enrichment was thought to make the more excess energy. However, because the plants under C0_2 enrichment condition grew as well as those under ambient condition, the excess energy might be wasted by activation of alternative system. Moreover, the CO_2-enrichment made the flux of CO_2 from atmosphere to carboxylation site at chloroplast more difficult.