Data from: Nitrifier controls on soil NO and N2O emissions in three chaparral ecosystems under contrasting atmospheric N inputs

Nitrogen saturation theory predicts high rates of atmospheric N deposition can increase ecosystem N availability and stimulate ecosystem N losses via soil nitric oxide (NO; an air pollutant at high concentrations) and nitrous oxide (N2O; a strong greenhouse gas) emissions. However, it remains unclear whether theories developed in mesic ecosystems apply to drylands, where plant and soil N availability are not always coupled in dry soils. NO and N2O are often produced in soils during the oxidation of ammonia by ammonia oxidizing archaea (AOA) or ammonia oxidizing bacteria (AOB) during nitrification. AOB are thought to emit more NO and N2O during nitrification than AOA and may be favored in N-rich relative to N-limited environments, suggesting high rates of atmospheric N deposition might produce positive feedback sending more of the N to the atmosphere. To assess how high rates of atmospheric N deposition affect AOB- and AOA-derived N trace gas emissions, we selectively inhibited AOA and AOB nitrifiers and measured NO and N2O emissions from soils collected from three dryland sites exposed to relatively low (3.8 kg ha-1 = Low N) or high (11.8 kg ha-1 = High N1; 15.6 kg ha-1 = High N2) rates of atmospheric N inputs. We found that while the High N2 deposition site had the lowest AOA:AOB ratio (2.33 ± 0.57), consistent with expectations, this site did not emit the most NO and N2O. Rather, AOA emitted between 21–78% of the NO from our sites, with higher AOA-derived NO emissions from relatively coarse-textured soils in the Low N deposition site. In addition to nitrification, denitrification also contributed to NO and N2O emissions, especially in the Moderate N deposition site (where denitrification-derived NO and N2O emissions were 2.0 – 3.7 time greater than the other sites), which had finer textured soils that may favor denitrification. Interactions between soil texture and N availability, therefore, appears to be the primary mechanism determining whether atmospheric N deposition is retained in the ecosystem or reemitted to the atmosphere as NO or N2O.