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

Biochar applied to soil can reduce nitrous oxide (N(2)O) emissions produced by freeze–thaw processes. Nonetheless, how biochar modification affects N(2)O 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 N(2)O emissions under different water conditions. The N(2)O emissions peaked at the initial stage of thawing in all the soils, and the total N(2)O 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 N(2)O emissions by 69 and 67%, respectively. Moreover, after biochar addition, the abundance of AOB amoA 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 N(2)O emissions and nitrification and denitrification communities. The PLS-PM further revealed that biochar can inhibit the production and emission of soil N(2)O by reducing soil MBN during soil thawing. In addition, soil moisture directly significantly affects N(2)O emissions and indirectly affects N(2)O emissions through its influence on soil physicochemical properties. Our results revealed the important function of biochar in decreasing the emission of N(2)O in flooded soil during freeze–thaw cycles.