A rapid increase of soil organic carbon in paddy fields after applying organic fertilizer with reduced inorganic fertilizer and water-saving irrigation is linked with alterations in the structure and function of soil bacteria

Abstract

The soil organic carbon (SOC), a direct reflection of carbon (C) sequestration, is associated with soil fertility, rice yield, and greenhouse gas emissions in paddy fields. Paddy field management practices are the primary cause of SOC changes. Aromatic rice, popular among consumers for its unique aroma, is cultivated and managed differently from conventional rice, and the underlying mechanisms of C sequestration in aromatic rice paddies have not been fully explored. Field experiments were conducted across two years, at five distinct ecological sites in Xingning (XN), Nanxiong (NX), Conghua (CH), Luoding (LD), and Zengcheng (ZC), implementing two treatments: inorganic fertilizer reduction combined with organic fertilizer and water-saving irrigation (IOW), and conventional cultivation (CC). C inputs from rice roots and straw, SOC content, CO₂ emission fluxes and totals, soil bacterial community composition and soil bacterial metabolic pathways were analyzed and measured. This study also investigated the interaction between SOC content and soil microbes in paddy fields under IOW treatment. The results showed that compared with CC, IOW significantly increased SOC content (16.5 %), reduced CO₂ emission fluxes and totals (11.6–18.5 %), enhanced aromatic rice yield (15.1 %) and 2-acetyl-1-pyrroline (2-AP) content (14.8 %). IOW significantly altered the soil bacterial community, enhanced C sequestration metabolic pathways and attenuated C consumption pathways in paddy fields, thereby increasing SOC content in aromatic rice paddies. Random forest analysis discovered that the most important bacteria associated with SOC content in paddy fields were Planctomycetota, Verrucomicrobia, and Gemmatimonadetes, while the most critical functions included other glycan degradation, CH₄ metabolism, and mannose type O-glycan biosynthesis. Additionally, IOW increased C inputs from straw and roots (3.1 % and 5.5 %, respectively), contributing to the increased SOC.