Nitrous oxide (N2O), a powerful trace gas, is closely associated with nitrite (NO2-) content in neutral and alkaline dryland soils, while this relationship has not been tested under soil acidification and crop rhizosphere. By examining key N transformations in maize rhizosphere and bulk soils along a pH gradient (4.2-6.8), we found that N2O emissions significantly declined with increasing acidity, particularly in the rhizosphere. This reduction was driven by decreased NO2- accumulation, resulting from stronger suppression of potential ammonia oxidation (NH3, PAO) than for NO2- oxidation (PNO). Acidification preferentially inhibited NH3-oxidizing bacteria and their core taxa relative to the nxrA-encoding NO2--oxidizer, thereby lowering the PAO/PNO ratio. Both NO2- and N2O were significantly enriched in the rhizosphere at pH above 5.2, whereas this positive effect disappeared at pH 4.2. Overall, increasing the pH may enhance rhizosphere N2O emissions by decoupling NH3 and NO2- oxidation, highlighting the importance of maintaining their balance when amending acidic soils.
Wang et al. (Wed,) studied this question.