中文摘要：

通过盆栽试验方法，采用^13C脉冲标记技术和稳定同位素质谱分析技术，研究了三个生育期（返青期、分蘖期和抽穗期）光合碳在“水稻-土壤”系统中的同化率、分配比率及其在土壤中增加率的动态变化，探讨三个生育期光合碳在“水稻-土壤”系统中的运转、分配规律，为明确稻田生态系统中碳素循环过程提供理论依据。结果表明，分别在返青期、分蘖期和抽穗期进行一次^13C脉冲标记（持续5h）后，光合碳在“水稻-土壤”系统中的总同化率均随标记后天数的延长呈逐渐下降趋势，从标记后2d至收获时，总同化率分别为75．92％～39．53％、70．01％～52．02％、86．38％～69．60％，且收获时与2d时的同化率差异均达显著水平（P〈0．05），其被同化光合碳的损失率分别为47．93％、25．70％和19．43％；抽穗期光合碳同化率明显高于返青期和分蘖期，被同化光合碳的损失也明显低于返青期和分蘖期。三个生育期被同化的光合碳向水稻地上部分和地下部分（包括根和土壤）的运转呈互相消长关系，但向水稻地上部分的分配比率（平均为85．04％～73．10％）远大于向根的分配比率（平均为12．50％～22．04％）和土壤的分配比率（平均为1．70％～5．04％），且抽穗期光合碳向水稻地上部分中的分配比率大于分蘖期和返青期，向地下部分的分配比率则正好相反；此外，三个生育期被同化的光合碳在土壤中的增加率分别为0．08％～0．21％、0．09％～0．17％和0．19％～0．27％，抽穗期土壤中光合碳的增加率要大于返青期和分蘖期，且光合碳在土壤中也相对稳定。

英文摘要：

[Objective] Photosynthetic carbon （C） , an important link of the carbon cycle in the atmosphere-plant-soil system, is closely related to the atmospheric environment and changes in soil quality, and plays a crucial role in the terrestrial ecosystem and global C cycling. Rice is one of the main grain crops in China, whose planting area is increasing year by year. Paddy soil is obviously quite high in C sequestration potential. Therefore, it is of vital significance to explore distribution of photosynthetic C in the paddy soil system and its variation to scientific evaluation of C cycling in paddy soil. [Method] 13C pulse-labeling and stable isotopic mass spectrometry technologies were employed to study variation of the assimilation rate and distribution ratio of photosynthetic C and their increasing rates in the rice-soil system relative to growth stage （ regreening, tillering and heading stages ） of the rice plants growing in a pot experiment. [Result] The objectives of this study were toexplore turnover and distribution dynamics of photosynthetic C in therice-soil system at three different growth stages of the plants and to provide a theoretical basis for further researches on C cycling and renewal of soil organic C in the paddy ecosystem. Results show that photosynthetic C gradually decreased in total assimilation rate with the each passing day after 13C pulse-labeling （duration 5 h） of the rice-soil system conducted, separately, at the beginning of each growth stage. The total assimilation rate reached 75.92% - 39.53%, 70.01% - 52.02% and 86.38% - 69.60% and the loss rate of assimilated photosynthetic C 47.93%, 25.70% and 19.43%, respectively, during the period from Day 2 after the labeling at the regreening, tillering and heading stageperiod. The assimilation rate of photosynthetic C was significantly higher in the heading stage than in the regreening and tillering stages, while an opposite trend was observed of the loss rate of photosynthetic C. The transformation of the photosynthetic C was offs