The rhizosphere microecological mechanisms underpinning high yield and carbon budget surplus in low-stubble ratoon rice

The ratoon rice is characterized by high yield and low emissions. Carbon sequestration and release within the paddy field ecosystem are significantly influenced by rhizosphere microorganisms. Nevertheless, the relationship between these processes and the nutritional strategies of microorganisms remains poorly understood. This study was conducted in 2023 and 2024 at the Rural Revitalization Research Institute Experimental Farm in Xiushui District, Putian City, Fujian Province (119°07′ E, 25°18′ N), in which two varieties with varying growth durations were utilized as experimental materials to examine the yield formation of the main crop (MC), ratoon season rice (RSR), and single cropping rice (LR), the dynamics of rhizosphere microorganisms, and the net ecosystem carbon balance (NECB) in paddy fields during the 2023—2024 period, as well as the underlying mechanisms influencing these processes. The results demonstrate that the average daily yield of the ratoon rice pattern (MC + RSR) in 2023—2024 was 11.02% to 28.83% higher compared to that of the single cropping rice system (LR) synchronously heading with RSR. An analysis of photosynthetic products indicates that the allocation of photo-assimilates to the rhizosphere of RSR decreased by 57.42% and 52.66% relative to that of MC and LR, respectively. An investigation on the nutritional strategies of rhizosphere microorganisms reveals that the abundance of autotrophic bacteria in RSR soil increased by 55.54% and 32.36% compared to that in MC and LR, respectively. Moreover, the analyses of GHGI and NECB in paddy fields demonstrated that the daily average carbon emission index of the rice ratooning pattern (MC+RSR) decreased by 52.42%~52.66% compared with that of the LR system. The comparative analysis reveals significant differences in carbon sink capacities between cropping patterns. The MC + RSR system demonstrates robust carbon sequestration performance, achieving a carbon budget surplus ranging from 17, 776.53 to 32, 845.15 kg CO₂-eq ha⁻¹. In contrast, the LR pattern exhibits relatively weaker carbon sink functionality with a surplus of only 5, 701.10 to 11, 665.04 kg CO₂-eq ha⁻¹. This divergence stems from two key mechanisms: Firstly, ratoon rice cultivation effectively extends the utilization period of light and thermal resources through its unique growth cycle configuration (main crop-ratooning rice), thereby enhancing photosynthetic carbon fixation efficiency. Secondly, the observed microbial community restructuring in rhizosphere soil—characterized by increased autotrophic bacterial populations (carbon-fixing species) and decreased heterotrophic bacterial abundance (carbon-decomposing species)—establishes a homeostasis mechanism in rhizosphere microecosystem. This is an important rhizosphere micro-ecological resilience response mechanism for carbon sequestration, carbon reduction and carbon balance surplus in rice ratooning practice.