Characteristics of greenhouse gas emissions from farmland soils based on a structural equation model: Regulation mechanism of biochar

Greenhouse gas (GHG) emissions from soil carbon and nitrogen cycles during freeze-thaw cycles (FTCs) provide positive feedback to climate warming. Biochar is a new type of soil conditioner that shows potential in soil GHG emissions reduction. To explore the mechanisms of the effects of biochar on soil GHG emissions in seasonally frozen soil areas, this study focused on farmland soil in the Songnen Plain. Variations in soil environmental factors, available carbon and nitrogen and microbial biomass were analyzed using an indoor simulation of soil FTCs. A structural equation model (SEM) was established to reveal the key driving factors and potential mechanism of biochar on soil GHG emissions under FTCs. The results showed that biochar increased carbon dioxide (CO2) emissions by 3.40% and methane (CH4) absorption by 2.52% and decreased nitrous oxide (N2O) emissions by 35.90%. SEM showed that soil temperature (ST) was the main environmental factor determining CO2 emissions and that soil moisture (SM) was the main environmental factor determining CH4 and N2O emissions. Soil available carbon and nitrogen and microbial biomass are important for soil GHG emissions as the reaction substrates and main participants in the biochemical transformation of soil carbon and nitrogen, respectively. This study showed that the application of biochar in farmland is a feasible choice to address climate change in the long term via soil carbon sequestration and GHG emissions reduction. The research results provide a theoretical basis and scientific guidance for soil GHG emissions reduction during FTCs in middle to high latitudes.