Abstract
Nitrification inhibitors (NIs) such as dicyandiamide (DCD), 3,4-dimethylpyrazole phosphate (DMPP), and allylthiourea (AT) are commonly used to suppress ammonia oxidization at different time scales varying from a few hours to several months. Although the responses of NIs to edaphic and temperature conditions have been studied, the influence of the aforementioned factors on their inhibitory effect remains unknown. In this study, laboratory-scale experiments were conducted to assess the short-term (24 h) influence of eight abiotic and biotic factors on the inhibitory effects of DCD, DMPP, and AT across six cropped and non-cropped soils at two temperature conditions with three covariates of soil texture. Simultaneously, the dominant contributions of ammonia-oxidizing archaea (AOA) and bacteria (AOB) to potential ammonia oxidization (PAO) were distinguished using the specific inhibitor 2 phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO). Our results revealed that AT demonstrated a considerably greater inhibitory effect (up to 94.9% for an application rate of 75 mg of NI/kg of dry soil) than DCD and DMPP. The inhibitory effect of AT was considerably affected by the relative proportions of silt, sand, and clay in the soil and total PAO. In contrast to previous studies, the inhibitory effects of all three NIs remained largely unaffected by the landcover type and temperature conditions for the incubation period of 24 h. Furthermore, the efficacy of all three tested NIs was not affected by the differential contributions of AOA and AOB to PAO. Collectively, our results suggested a limited influence of temperature on the inhibitory effects of all three NIs but a moderate dependence of AT on the soil texture and PAO. Our findings can enhance the estimation of the inhibitory effect in soil, and pure cultures targeting the AOA and AOB supported ammonia oxidization and, hence, nitrogen dynamics under NI applications.
Highlights
Soil nitrification has been observed at temperatures as low as 2 ◦ C [7], whereas ammonia-oxidizing archaea (AOA) isolated from croplands, non-croplands, and geothermal sources mostly exhibited temperature optima of >35 ◦ C [4,8,9,10]
Nitrification inhibitors (NIs) have been used to suppress the activity of ammonia oxidizers and, nitrification and nitrous oxide emissions from terrestrial and agricultural ecosystems
The inhibitory effect (IE) of DCD, dimethylpyrazole phosphate (DMPP), and AT were largely independent of the edaphic conditions and temperatures over the short-term incubation period (24 h)
Summary
Ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) majorly dominate ecosystem functioning by modulating the rate of nitrification in terrestrial and aquatic ecosystems [1,2,3,4]. Ammonia oxidation is carried out by complete ammonia oxidizers (comammox) [5,6]. Soil nitrification has been observed at temperatures as low as 2 ◦ C [7], whereas AOA isolated from croplands, non-croplands, and geothermal sources mostly exhibited temperature optima of >35 ◦ C [4,8,9,10]. Nitrification is an essential process of N dynamics in the ecosystem, it results in N fertilizer loss and environmental pollution in agricultural ecosystems through nitrate leaching and nitrous oxide (N2 O)
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