CO₂ and CH₄ emission from paddy field play a crucial role in the global greenhouse gas emission and terrestrial ecosystem C cycle. The emitted C mainly derives from rhizosphere respiration and microbial decomposition of soil organic matter (SOM). Living roots can regulate SOM decomposition via rhizosphere processes which is defined as rhizosphere priming effect (RPE). Many investigations exist on RPE in upland soils. However, much less attention has been paid to RPE and CH₄ emission in flooded paddy soil. Therefore, quantifying the RPE on CH₄ emission with synergistic effects of rice growth and N fertilizers in rice paddies requires further investigation.

Researchers in the Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA) invented a CO₂ and CH₄ trapping system and employed ¹³C continuous labelling techniques to investigate how N fertilization influence RPE on CO₂ and CH₄ release from in a paddy field ecosystem. The team found that rice root growth and rhizodeposits affected the direction of the RPE for CO₂, which first decreased below zero (before 40 days), but rose above zero (after 52 days). The RPE on CH₄ was always above zero, and gradually increased with rice growth in relation to the amount of rhizodeposits and the decrease of soil redox potential. Furthermore, N fertilization reduced N limitation, decreased the potential of microorganisms to decompose SOM to meet their N needs, and lowered the magnitude of RPE for both CO₂ and CH₄. Overall, N fertilization and rice growth affected the RPE for CO₂and CH₄ by altering microbial activity in paddy soil.

This study firstly showed that root-microbial interactions stimulated SOM mineralization in rice paddies through rhizosphere priming effects not only for CO₂ but also for CH₄. The RPE, however decreased with N fertilization. The important implication is that “optimized N fertilization is necessary to mitigate greenhouse gas emissions from rice field ecosystems by maintaining high C input by roots and so, high C sequestration” said ZHU Zhenke, an assistant researcher in ISA.

This research was supported by funding from the National Natural Science Foundation of China [grant numbers 41671292, 41501321, 41771337], the National Key Research and Development program [grant number 2016YFE0101100], the Youth Innovation Team Project of Institute of Subtropical Agriculture, Chinese Academy of Sciences [grant number 2017QNCXTD_GTD], and the Open Fund of Key Laboratory of Agro-ecological Processes in Subtropical Region, Chinese Academy of Sciences [grant number ISA2017301]. We thank Public Service Technology Center, Institute of Subtropical Agriculture, Chinese Academy of Sciences for technical assistance. The publication was prepared with the support of the “RUDN University program 5-100”.

The study, titled “Rice rhizodeposits a？ect organic matter priming in paddy soil: The role of N fertilization and plant growth for enzyme activities, CO₂ and CH₄ emissions” has been published in Soil Biology and Biochemistry, details could be found at https://www.sciencedirect.com/science/article/pii/S0038071717306405.

Contact: GE Tida

E-mail: gtd@isa.ac.cn

Institute of Subtropical Agriculture, Chinese Academy of Sciences

Conceptual diagram of rhizosphere priming effect for CO₂ and CH₄ depending on rice growth an N fertilization.