Methane (CH₄), which is an important component of the greenhouse gases from paddy ecosystems, is a major contributor to climate change. CH₄ emissions from paddy ecosystems are closely related to the rice root system; however, how the rice root system affects CH₄ emissions remains unclear. We conducted a field experiment in 2023 at the Heping Irrigation District Rice Irrigation Experiment Station in Qing’an County, Heilongjiang Province. The field experiment used five local rice varieties with similar fertility periods to observe rice root morphology and physiology indexes, CH₄ emission fluxes, and cumulative CH₄ emissions. A structural equation model (SEM) was established to investigate the effects of root characteristics on the CH₄ emissions from rice and understand the potential mechanisms of these effects. The results showed that the seasonal patterns of CH₄ emission fluxes were similar in different rice varieties, and that, during the tillering to heading–flowering stages, the cumulative CH₄ emissions accounted for 89.8–92.6% of the total cumulative CH₄ emissions of rice. Significant negative correlations were observed between CH₄ emission fluxes and root volume, root dry weight, root oxidation activity (ROA), and root radial oxygen loss (ROL) (r = −0.839, −0.885, −0.401 and −0.934, p < 0.05), while there were significant positive correlations between root diameter; malic acid, citric acid, and succinic acid contents; and CH₄ emission fluxes (r = 0.407, 0.753, 0.797, and 0.685, p < 0.05). The SEM showed that CH₄ emission fluxes were directly influenced by ROL and organic acid contents, while the other root indicators had indirect effects by modulating ROL and organic acid contents. ROL and root volume had the largest total effect, indicating that ROL and root volume were the most significant root physiological and morphological indicators affecting CH₄ emission fluxes. This study provides theoretical support and reference data for achieving sustainable agricultural development in the black soil region of Northeast China.

Paddy fields are important anthropogenic emission sources of methane (CH₄). However, it is not clear how rice root development and rhizosphere soil properties affect CH₄ emissions. Therefore, we selected rice varieties with similar growth periods but different root traits in the local area. We measured CH₄ emission fluxes, cumulative CH₄ emissions, root dry weight, root length, and the dissolved organic carbon (DOC), microbial biomass carbon (MBC), redox potential (Eh), ammonium nitrogen (${\mathrm{N}\mathrm{H}}_4^{+}$–N), and nitrate nitrogen (${\mathrm{N}\mathrm{O}}_3^{-}$–N) contents in rhizosphere soil. Methanogens and methanotrophs are crucial factors influencing CH₄ emissions; thus, their abundance and community composition were also assessed. The result showed that CH₄ fluxes of each rice variety reached the peak at tillering stage and jointing-booting stage. The CH₄ emissions in tillering stage were the largest in each growth period. CH₄ emissions had negative correlations with root length, root dry weight, Eh ${\mathrm{N}\mathrm{O}}_3^{-}$–N, methanotroph abundance, and the pmoA/mcrA ratio, and positive correlations with ${\mathrm{N}\mathrm{H}}_4^{+}$–N, MBC, DOC, and methanogen abundance. Path analysis confirmed methanogens and methanotrophs as direct influences on CH₄ emissions. Root development and rhizosphere soil properties affect CH₄ emissions indirectly through these microbes. This study suggests that choosing rice varieties with good root systems and managing the rhizosphere soil can effectively reduce CH₄ emissions.

Straw return is an effective measure to increase soil sustainability. However, few studies have examined the effects of different straw return methods on soil structure, soil organic carbon content and maize yield or the potential relationships between those variables. Therefore, we developed a field orientation experiment to study the effects of different straw return methods on soil porosity, soil aggregate stability, the soil organic carbon content and maize yield. Four treatments were established: flat no-tillage with full straw mulching (FM), ridge no-tillage with full straw mulching (LM), rotary tillage with full straw incorporation (LX), and conventional tillage without straw (CK) as the control treatment. Compared with those of the CK treatment, the soil porosities (f) in the FM, LM and LX treatments significantly increased by 6.7%, 8.8% and 7.9%, respectively; the soil aggregate destruction rates (PAD) decreased by 17.3%, 34.3% and 16.9%, respectively. In addition, the FM, LM and LX treatments effectively increased the mean mass diameters (MWDs) of the soil aggregates and the soil organic carbon content. Compared with those in the CK treatment, the three-year average yields in the FM, LM and LX treatments significantly increased by 5.2%, 7.2% and 4.1%, respectively. Moreover, the f, MWD, soil organic carbon content and corn yield were positively correlated. Our study indicates that the LM treatment was most effective in improving soil structure and increasing soil organic carbon content with corn yield.