Effects of biochar addition on greenhouse gas emissions during freeze–thaw cycles in a black soil region, Northeast China

Abstract As global warming intensifies, the soil environment in middle to high latitudes will undergo more extensive and frequent freeze–thaw cycles (FTCs), which will significantly affect the carbon and nitrogen cycles of soil ecosystems and aggravate greenhouse gas (GHG) emissions. Biochar can increase soil organic carbon storage and mitigate climate change. To effectively control GHG emissions, soil supplemented with biochar at different application rates (0%, 2%, 4% and 6% [w/w]) under different numbers of FTCs (0, 3, 6, 9, and 12) was selected as the research object. The soil GHG emission characteristics in different experimental treatments and their relationships with soil physical and chemical properties were determined. Our results showed that N 2 O and CO 2 emissions were promoted during FTCs, with values of 3.13–50.37 and 16.22–135.50 μg m −2 h −1 , respectively. The order of N 2 O and CO 2 emissions with respect to biochar application rate was as follows: 2% > 0% > 4% > 6%. CH 4 emissions were negative during FTCs, varying from −1.62 to −10.59 μg m −2 h −1 , and negative CH 4 emissions were promoted by biochar. Correlation analysis showed that N 2 O, CO 2 and CH 4 emissions were significantly correlated with pH, soil moisture and soil organic matter (SOM), total nitrogen (TN) and –N contents ( p < .01). The conceptual path model demonstrated that GHG emissions were significantly influenced by FTCs, moisture, SOM and biochar application rate. Our results indicate that the effects of FTCs on GHG emissions were greater than those of biochar application. Biochar application rates of 4% or 6% should be considered in the future to reduce soil GHG emissions in the black soil region of Northeast China. Our results can help provide a theoretical basis and effective strategy to reduce soil GHG emissions during FTCs in seasonally frozen regions.