Rice is a primary source of food that feeds more than half of the world’s population. Rice paddy ecosystems, which covered a total area of more than 160 million hectares worldwide, plays an important role in mitigating the increasing concentration of atmospheric CO₂.

Photosynthesis is the main pathway to capture carbon (C) into rice plant. Straw returning, root residue, and rhizodeposition are the main approaches for the C input into rice field. In addition, nitrogen (N) fertilization modifies the allocation and dynamics of photosynthates in paddy rice systems. However, N fertilization impact on the distribution, transformation, and fates of photosynthetic C in rice-soil systems is poorly understood.

Through a multiple pulse-labelling with ¹³CO₂ method, researchers from the Institute of Subtropical Agriculture (ISA) of the Chinese Academy of Sciences quantified the rice photosynthesis-derived C input into the rice-soil systems, and estimated the effect of N fertilization on the distribution and fates photosynthesized carbon in rice-soil systems.

The researchers found the assimilated C in the roots and rhizosphere soil was largest at the early growth stage (tillering) and subsequently decreased. At harvest, 68% of the rhizodeposited C remained in bulk soil without N fertilizer, which corresponded to 6.2% of the net assimilated C.

The absolute amount of net belowground C input (root + rhizodeposition) by rice was 268 and 468 kg C ha^-1 under 0 and 225 kg N ha^-1 fertilizer, of which rhizodeposition accounted for 60 and 40%, respectively. This indicates that N fertilization raised the belowground C input by rice mainly by increasing root biomass rather than by rhizodeposition.

However, although the net distribution of assimilated C to belowground pools did not change, N fertilization promoted C assimilation in aboveground biomass. N fertilization induced higher mass-specific rhizodeposition (per unit root dry weight) and its turnover rate compared with the unfertilized system. With higher microbial turnover, the daily C allocation from roots to soil was similar at both fertilization levels.

Researchers revealed that although total C input into soil is enhanced by N fertilization, its further fate is N fertilization independent, thus leading to a net accumulation of C input in rice paddy soil similar to that observed unfertilized soil.

Related studies, published in European Journal of Soil Science and Plant and soil were supported by the National Key Research and Development Program, the Australia-China Joint Research Centre-Healthy Soils for Sustainable Food Production and Environmental Quality, the National Natural Science Foundation of China, Hunan Province Base for Scientific and Technological Innovation Cooperation, Open Fund of Key Laboratory of Agro-ecological Processes in Subtropical Region, Chinese Academy of Sciences, the Youth Innovation Team Project of ISA, CAS, the Open Research Fund of State Key Laboratory of Hybrid Rice, Hunan Hybrid Rice Research Center and the Natural Science Foundation of Hunan Province of China.

Contact: GE Tida

E-mail: gtd@isa.ac.cn

Institute of Subtropical Agriculture, Chinese Academy of Sciences