Soil acidification induced variation of nitrifiers and denitrifiers modulates N₂O emissions in paddy fields

Soil acidification is a major land degradation process globally, and impacts soil nitrogen (N) transformation. However, it is still not well known how soil acidification affects net N mineralization and nitrification, especially N-cycling microbes and nitrous oxide (N₂O) emissions. Hence, three soils characterized by different soil pH values (5.5, 6.3, and 7.7) were collected from the paddy fields, and experiments were conducted to evaluate the effect of soil acidification on net N mineralization and nitrification, and N₂O emissions. Compared to those in the soils with pH 7.7 and 6.3, net N mineralization, net nitrification, and N₂O emissions were decreased by 75-76 %, 89-91 %, and 19-48 %, respectively, in the soil with pH 5.5, while net N nitrification and N₂O emissions decreased by 18 % in the soil with pH 6.3 when compared to those in the soil with pH 7.7. The significantly decreased net nitrification in the soils with pH 6.3 and 5.5 was mainly attributed to the limited N availability and abundance of nitrification-related microbes including ammonia-oxidizing bacteria and complete ammonia-oxidizers. The decrease in N₂O emissions of soils with pH 6.3 and 5.5 had mainly resulted from decreasing nitrification and denitrification via suppressing microbes including nirS and fungal nirK and limiting N availability. Hence, this study provides new insights and improves our understanding of how soil acidification regulates N mineralization, nitrification, and N₂O emissions in paddy soils, which gives guidance on developing N management strategies for sustainable production and N₂O mitigation in acid soils.