Managing soil pH has been recognized as one of the promising options for N2O emission mitigation in acidic soils. Rice-straw biochar (BC) application to acidic soils can not only ameliorate soil acidity but also influence N2O emissions. We investigated the impact of various levels of rice-straw-derived biochar, a control (no biochar), 2% biochar, and 4% biochar under 50% and 90% water-filled pore space (WFPS) values. In comparison with the application of biochar at 2%, the application of biochar at 4% more pronouncedly altered soil properties (pH, ammonium (NH4+-N), nitrate (NO3-N), microbial biomass carbon (MBC), and abundance of nosZ and nirK genes). Similarly, more noticeable changes in soil properties were noted under 90% WFPS than under 50% WFPS. The soil pH increased from 5.67 to 7.29 with the 4% biochar application. In comparison with those following the 2% biochar application and the control, soil mineral N and the abundance of nosZ and nirK genes following the 4% biochar application were more augmented, thereby leading to a remarkable reduction in soil N2O emissions. The MBC content in the soil also increased with the BC applications, and the maximum MBC contents of 655 and 428 mg kg−1 dry soil were recorded with the 4% biochar application under 50% and 90% WFPS, respectively. Moreover, in comparison with the control, 4% BC mitigated soil N2O emissions by 83%, whereas cumulative N2O emissions were mitigated by 49%. In comparison with 90% WFPS, 50% WFPS produced 35% more N2O emissions. However, the biochar applications significantly (p < 0.05) reduced N2O emissions under both WFPS values owing to an increase in soil pH, which activated mineral N (NH4+-N and NO3−-N) and enhanced the abundance of nosZ and nirK genes. These results suggest that biochar applications can substantially diminish soil N2O emissions by triggering soil pH, soil C and N pools, and the abundance of nosZ and nirK genes.

中文翻译：

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不同水分条件下施用生物炭后酸性土壤中的 N2O 排放减缓

管理土壤 pH 值已被公认为减少酸性土壤中 N2O 排放的有希望的选择之一。稻草生物炭 (BC) 应用于酸性土壤不仅可以改善土壤酸度，还可以影响 N2O 排放。我们研究了不同水平的稻草衍生生物炭、对照（无生物炭）、2% 生物炭和 4% 生物炭在 50% 和 90% 充水孔隙空间 (WFPS) 值下的影响。与施用 2% 的生物炭相比，施用 4% 的生物炭更显着地改变了土壤性质（pH、铵 (NH4+-N)、硝酸盐 (NO3-N)、微生物生物量碳 (MBC) 和丰度） nosZ 和 nirK 基因）。同样，在 90% WFPS 下比在 50% WFPS 下注意到土壤特性的更显着变化。施用 4% 的生物炭后，土壤 pH 值从 5.67 增加到 7.29。与施用 2% 生物炭和对照相比，施用 4% 生物炭后土壤矿物质 N 和 nosZ 和 nirK 基因的丰度增加更多，从而导致土壤 N2O 排放量显着减少。土壤中的 MBC 含量也随着 BC 的应用而增加，在 50% 和 90% WFPS 下，4% 生物炭应用记录的最大 MBC 含量分别为 655 和 428 mg kg-1 干燥土壤。此外，与对照相比，4% BC 使土壤 N2O 排放量减少了 83%，而累积 N2O 排放量减少了 49%。与 90% WFPS 相比，50% WFPS 产生的 N2O 排放量增加了 35%。然而，由于土壤 pH 值的增加，在两个 WFPS 值下，生物炭应用显着（p < 0.05）减少了 N2O 排放，它激活了矿物质 N（NH4+-N 和 NO3--N）并增加了 nosZ 和 nirK 基因的丰度。这些结果表明，生物炭应用可以通过触发土壤 pH 值、土壤 C 和 N 库以及 nosZ 和 nirK 基因的丰度来显着减少土壤 N2O 排放。