Rhizosphere microecological mechanism of carbon sequestration and its emission mitigation in rice ratooning

Abstract

Rice ratooning plays a critical role in mitigating global climate change and enhancing soil carbon sequestration due to its properties of carbon fixation and emission reduction. The rhizosphere micro-ecosystem emerges as one of the key determinants, thus it is highly significant to investigate the impact changes in rhizosphere microbial composition on the ecological mechanisms associated with carbon sequestration and emission reduction in paddy fields. Over two consecutive years, this study analyzed greenhouse gas emission characteristics, photosynthetic carbon assimilation patterns, and rhizosphere microenvironmental differences between the main crop (MC) and ratoon season rice (RSR) using four rice varieties with distinct growth stages and genetic traits. The results demonstrated that compared to MC, RSR reduced the daily average methane (CH₄) emissions from paddy field by 57.78∼64.31 %, while decreasing the distribution of photosynthetic products to the rhizosphere soil by 78.15 %. 16S rRNA sequencing revealed a significant increase in the abundance of autotrophic microorganisms, and the carbon-fixing bacterium Pseudarthrobacter was isolated and identified in RSR soil. The exogenous addition of this microorganism increased the soil organic carbon (SOC) content of RSR by 4.65 %, while simultaneously reducing CH₄ emissions from paddy fields by 26.25 %. The significant increase in autotrophic carbon-fixing bacteria in the rhizosphere soil is one of the key micro-ecological mechanisms driving carbon sequestration and emission reduction in paddy fields. This is attributed to the reduced allocation of photosynthetic carbon assimilation products to the belowground components, thereby promoting the abundance of autotrophic carbon-fixing bacteria in RSR field. Consequently, the ecological niche width of heterotrophic microorganisms, such as methanogens, is reduced, while autotrophic carbon-fixing bacteria mitigate greenhouse gas emissions from RSR field by fixing CO₂ and increasing SOC content. The findings offer valuable theoretical and practical perspectives on attaining the overarching objectives of carbon neutrality and food security.