Effect of CO_2 enrichment on carbon metabolism of rice plants

本研究考察了CO_2富集对水稻植株碳代谢的影响。首先，以自由空气co_2富集项目稻田的水稻植株为研究对象，研究了co_2富集对13C对光合产物分配和转运的影响。结果表明，在co_2富集条件下生长的植株光合产物比环境条件下生长的植株更有效地向穗部转移。此外，在co_2富集条件下生长的植株，抽穗期叶鞘中储存的淀粉转移到穗部的速度比环境条件下更快。这说明co_2的富集促进了碳向汇器官（耳）的转运和分配。其次，研究不同浓度co2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逐渐减少。因此，C0_2的富集被认为产生了更多的多余能量。然而，由于co2富集条件下的植物生长和环境条件下的植物生长一样，多余的能量可能会被激活替代系统而浪费掉。此外，CO_2富集使CO_2从大气到叶绿体羧基化位点的通量变得更加困难。

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.