[Allocation and Stabilization Responses of Rice Photosynthetic Carbon in the Plant-Soil System to Phosphorus Application].

This research studied the response of the input and allocation of photosynthetic carbon (C) to phosphorus (P) in paddy soils. Two treatments were conducted in this experiment:no P application (P0) and the application of 80 mg·kg-1 of P (P80). The rice cultivar was the indica Zhongzao 39. The 13C-CO2 continuous labeling technique was used to identify the photosynthetic C distribution of the rice. The results showed that the application of P80 significantly increased the photosynthates allocation in the rice aboveground, but reduced their allocation in the rhizosphere soil (P<0.05). At the jointing stage, P80 application increased the photosynthetic C content of the rice by 70%, but the root dry weight decreased 31%. Compared with P0, the total C content of the aboveground rice was increased 0.31 g·pot-1 by P80. The ratio of rice roots to shoots decreased with the P80 treatment. Moreover, P80 application led to an increase in the photosynthetic microbial biomass in the non-rhizosphere soil C (13C-MBC) of 0.03 mg·kg-1, but still decreased its allocation in the rhizosphere soil. The allocation of photosynthetic C to the particulate organic matter fraction (POC) and mineral fraction (MOC) in the non-rhizosphere soil showed no significant differences between P0 and P80. Additionally, the P80 fertilization treatment significantly lowered the content of POC in the rhizosphere soil. In summary, P application increased the allocation of photosynthetic C in the soil-rice system, but reduced the accumulation of photosynthetic C in the soil. This research provided a theoretical basis and data supporting the rational application of P fertilizer, and was also of great significance as a study of the transportation and allocation of photosynthetic C and its sequestration potential response to the application of P to the rice soil.

[Effect of CO2 Doubling and Different Plant Growth Stages on Rice Carbon, Nitrogen, and Phosphorus and Their Stoichiometric Ratios].

The variation characteristics of ecological stoichiometric ratios can reflect the nature of plant adaptation to environmental changes. The C, N, and P contetns, and their stoichiometric ratios in different organs of rice were studied using a CO2 continuous labeling system, by simulating the increase of atmospheric CO2 concentration (800×10-6). The results showed that CO2 doubling promoted the growth of rice organs and increased the root/shoot ratio. CO2 doubling reduced the shoot TN content in different growth periods, increased the C/N ratio in the rice root, shoot, and grain, decreased the N use efficiency, and improved the P use efficiency. Multiple comparison and Venn diagram analyses showed that CO2 concentration only has a significant impact on the TN content in the rice shoot; it contributed little to the variation in rice nutrient content and their stoichiometric ratios, indicating that CO2 doubling had no effect on these. Under the condition of elevated atmospheric CO2 concentrations, the C, N, and P contents and their stoichiometirc ratios, in rice organs had good homeostasis, and the stoichiometric change during growth periods was consistent with "the Growth Rate Theory". In farmland management, appropriate nitrogen fertilizers can alleviate the nutrient balance pressure caused by the increase in CO2 concentration.