Effects of biochar addition on nitrous oxide emission during soil freeze–thaw cycles

Biochar applied to soil can reduce nitrous oxide (N₂O) emissions produced by freeze-thaw processes. Nonetheless, how biochar modification affects N₂O emissions during freeze-thaw cycles is not completely clear. In our research, during freeze-thaw cycles, microcosm experiments were conducted to investigate the effects of maize straw biochar (MB) or rice straw biochar (RB) addition on soil N₂O emissions under different water conditions. The N₂O emissions peaked at the initial stage of thawing in all the soils, and the total N₂O emissions were considerably greater in the flooded soils than in the nonflooded soils. Compared with the soils without biochar addition, RB and MB amendments inhibited N₂O emissions by 69 and 67%, respectively. Moreover, after biochar addition, the abundance of AOB <i>amoA</i> genes decreased by 9-13%. Biochar addition significantly decreased the content of microbial biomass nitrogen (MBN) in flooded soil during thawing, which was significantly correlated with N₂O emissions and nitrification and denitrification communities. The PLS-PM further revealed that biochar can inhibit the production and emission of soil N₂O by reducing soil MBN during soil thawing. In addition, soil moisture directly significantly affects N₂O emissions and indirectly affects N₂O emissions through its influence on soil physicochemical properties. Our results revealed the important function of biochar in decreasing the emission of N₂O in flooded soil during freeze-thaw cycles.