3,4-Dimethylpyrazole phosphate (DMPP) has been widely employed to reduce nitrogen leaching and greenhouse gas emissions in the soils of dry farmlands. However, the effects of DMPP on the dynamics of nitrogen in paddy fields remain unclear. For this study, treatments with 0%, 0.25%, 0.5%, 1%, or 1.5% DMPP levels of nitrogen fertilization plus urea were designed to determine the effects on greenhouse gas emissions in paddy fields of subtropical China. All DMPP treatments significantly reduced CH4 and N2O emissions, from 54% to 34%, and 94% to 39%, respectively, compared with a urea fertilizer treatment alone. The soil NH4+ content decreased and NO3− increased more slowly with the application of DMPP. The crop yields under the various DMPP treatments showed no significant difference (p < 0.05). We concluded that the application of 0.5% and 1% DMPP may significantly reduce CH4 and N2O emissions in contrast to other treatments. This has important implications for the maintenance of rice yields, while reducing greenhouse gas emissions in paddy fields.

Appropriate agricultural practices for carbon sequestration and emission mitigation have a significant influence on global climate change. However, various agricultural practices on farmland carbon sequestration usually have a major impact on greenhouse gas (GHG) emissions. It is very important to accurately quantify the effect of agricultural practices. This study developed a platform—the Denitrification Decomposition (DNDC) online model—for simulating and evaluating the agricultural carbon sequestration and emission mitigation based on the scientific process of the DNDC model, which is widely used in the simulation of soil carbon and nitrogen dynamics. After testing the adaptability of the platform on two sampling fields, it turned out that the simulated values matched the measured values well for crop yields and GHG emissions. We used the platform to estimate the effect of three carbon sequestration practices in a sampling field: nitrogen fertilization reduction, straw residue and midseason drainage. The results indicated the following: (1) moderate decrement of the nitrogen fertilization in the sampling field was able to decrease the N₂O emission while maintaining the paddy rice yield; (2) ground straw residue had almost no influence on paddy rice yield, but the CH₄ emission and the surface SOC concentration increased along with the quantity of the straw residue; (3) compared to continuous flooding, midseason drainage would not decrease the paddy rice yield and could lead to a drop in CH₄ emission. Thus, this study established the DNDC online model, which is able to serve as a reference and support for the study and evaluation of the effects of agricultural practices on agricultural carbon sequestration and GHG emissions mitigation in China.

Greenhouse gas (GHG) emissions are an important part of the carbon (C) and nitrogen (N) cycle in forest soil. However, soil greenhouse gas emissions in dawn redwood (Metasequoia glyptostroboides) stands of different ages are poorly understood. To elucidate the effect of plantation age and environmental factors on soil GHG emissions, we used static chamber/gas chromatography (GC) system to measure soil GHG emissions in an alluvial island in eastern China for two consecutive years. The soil was a source of CO₂ and N₂O and a sink of CH₄ with annual emissions of 5.5–7.1 Mg C ha⁻¹ year⁻¹, 0.15–0.36 kg N ha⁻¹ year⁻¹, and 1.7–4.5 kg C ha⁻¹ year⁻¹, respectively. A clear exponential correlation was found between soil temperature and CO₂ emission, but a negative linear correlation was found between soil water content and CO₂ emission. Soil temperature had a significantly positive effect on CH₄ uptake and N₂O emission, whereas no significant correlation was found between CH₄ uptake and soil water content, and N₂O emission and soil water content. These results implied that older forest stands might cause more GHG emissions from the soil into the atmosphere because of higher litter/root biomass and soil carbon/nitrogen content compared with younger stands.

Soil organic carbon (SOC) stabilization is largely governed by the accumulation of microbial necromass carbon, yet how stabilization is influenced by root exudation remains poorly understood, particularly under long-term nitrogen (N) fertilization. Here, we investigated SOC dynamics in paddy soil under long-term N fertilization (12 years, urea) at four application rates (0, 100, 200, and 300 kg N ha⁻¹). We quantified root exudate inputs, microbial community composition, microbial necromass, and soil physicochemical properties to identify the primary drivers of SOC accumulation. Our results showed that SOC content increased progressively with N application rate and these changes were attributable to N-induced increases in root exudate inputs, alterations to microbial community structure, and enhanced accumulation of microbial necromass. Structural equation modeling further revealed that root exudates served as a critical linkage between N fertilization, microbial necromass accrual, and SOC stabilization. Taken together, our findings imply that long-term N fertilization enhances SOC accumulation by stimulating root exudate-driven microbial necromass accrual, highlighting the pivotal role of plant–soil interactions in regulating carbon dynamics in rice agroecosystems.