Soil environment, carbon and nitrogen cycle functional genes in response to freeze-thaw cycles and biochar

Freeze-thaw cycles (FTCs) are a common phenomenon in seasonal frozen soil areas, which can significantly affect the changes in the soil environment and functional genes of microorganisms. To explore the effect of biochar application on soil carbon and nitrogen cycling under FTCs, an indoor soil column simulation test was used in this study. The experimental setup included different application rates of biochar (0%, 1%, 2%), with the carbon and nitrogen cycle functional genes serving as indicator genes. Real-time fluorescence quantitative PCR technology was employed for analysis. Based on the correlation heat map and redundancy analysis (RDA), the response mechanism of soil environment changes and carbon and nitrogen cycle functional genes before and after FTCs was analyzed. The results revealed that the application of biochar significantly increased soil's water-holding capacity held available nutrients in soil, and increased the ability of environmental change. Due to the influence of soil moisture and aeration, biochar reduced the variation of soil carbon sequestration gene cbbL, cbbM, and nitrogen fixation gene nifH abundance after FTC. The application of 2 % biochar significantly increased the abundance of the nitrification gene amoA and denitrification gene nirK and enhanced the respiration of soil microorganisms. Soil moisture (SM) is the main environmental factor that determines the abundance changes of the soil carbon sequestration genes cbbL and cbbM. Soil organic matter (SOM), pH, nitrate nitrogen (NO3−-N), and ammonium nitrogen (NH4+-N) were the main environmental factors determining the abundance of soil nitrogen fixation gene nifH, nitrification gene amoA, and denitrification gene nirK. This study can provide new insights into the internal mechanism of the soil carbon and nitrogen cycle in seasonal frozen soil areas, and provide some reference for the rational application of biochar and the efficient utilization of water and soil resources in seasonal frozen soil areas in the future.