[Dynamics of Rice Photosynthesized Carbon Input and Its Response to Nitrogen Fertilization at the Jointing Stage: C-CO Pulse-labeling].

Photosynthesized carbon (C) is an important source of soil organic C in paddy fields, and its input and distribution are affected by rice growth and soil fertility. Fertilizer application plays an important role in rice growth. The C pulse-labeling method was used to quantify the dynamics and distribution of input photosynthesized C in the rice-(rhizosphere-and bulk-) soil system and its response to nitrogen fertilizer (N) application. The results suggested that N fertilization significantly increased the rice aboveground and the root biomass and decreased the rice biomass root/shoot ratio. The amount of assimilated C gradually decreased in the rice plants but gradually decreased over 0-6 days and increased over 6-26 days in the rhizosphere and bulk soil during rice growth. N fertilization significantly increased the amount of assimilated C in the rhizosphere soil by 9.5%-32.6% compared with the control. In comparison to the unfertilized treatment, the application of N fertilization resulted in higher photosyntheticC in rice aboveground and in the root by 24.5%-134.7% and 9.1%-106%, respectively. With the N fertilized and unfertilized treatments, 85.5%-93.2% and 91.3%-95.7%, respectively, of input photosynthetic C was distributed in the rice plants. The results suggested that N fertilization significantly affected the distribution of photosynthesized C in the rice-soil system (<0.01). After 26 days of pulse labeling, the distribution of photosynthetic C into rice aboveground was increased by 13.4%, while the distribution into the rhizosphere and bulk soil were decreased by 21.9% and 52.2%, respectively, in the N fertilized treatments compared with the unfertilized treatments. Therefore, the N application increased the distribution of photosynthesized carbon in the soil-rice system but decreased the accumulation in the rhizosphere and bulk soil. The findings of this study provided a theoretical basis for our understanding of the dynamic of photosynthetic C in the plant-soil system and the assimilation of the soil organic matter pool in the paddy soil ecosystem.