Effects of the Nitrification Inhibitor Acetylene on Nitrous Oxide Emissions and Ammonia-Oxidizing Microorganisms of Different Agricultural Soils Under Laboratory Incubation Conditions.

Acetylene (C₂H₂) is an effective nitrification inhibitor targeting autotrophic ammonia oxidizers, and has shown promise for improving nitrogen use efficiency, mitigating greenhouse gas nitrous oxide (N₂O) emissions and reducing nitrate leaching. Its efficacy, however, varies considerably with edaphic and environmental conditions and remains largely less studied in dryland agricultural soils. Here we conducted two laboratory microcosm incubations to explore the efficacy of C₂H₂ across various agricultural soils and under different conditions. The first incubation was with four agricultural soils at 25°C and 60% water-filled pore space (WFPS), and the second incubation included one cropping soil under a range of conditions (15°C, 25°C, 35°C and 50%, 70% WFPS). Our results showed that incubation of soil with 1% v/v C₂H₂ resulted in complete or partial inhibition of nitrification, N₂O emission, and AOA or AOB growth in all conditions. Acetylene can totally inhibit nitrification in acidic cropping and dairy pasture soils through retarding both AOA and AOB growth, while C₂H₂ partly inhibited nitrification and N₂O emission through impeding only AOB in the alkaline vegetable soil. The highest inhibition effect of C₂H₂ was achieved at 25°C and 50% WFPS, while there was no inhibitory effect of C₂H₂ when soil was incubated at 15°C and 50% WFPS suggesting soil temperature may have a significant influence on C₂H₂ effectiveness. The inhibition of C₂H₂ on cumulative N₂O emission increased with increasing temperature at 50% WFPS. In contrast, at 70% WFPS, the inhibition of C₂H₂ on cumulative N₂O emission decreased with increasing temperature. Since the effect of C₂H₂ varied with soils and environmental conditions, this highlights the assumption that N₂O production and nitrification can be affected by low concentrations of C₂H₂may be not appropriate in some occasions. For better use of nitrification inhibitor it is important to understand that this will depend on the conditions present.