Comparisons of the effects of different drying methods on soil nitrogen fractions: Insights into emissions of reactive nitrogen gases (HONO and NO)

Abstract

Reactive nitrogen (N r ) emission from soils, e.g., nitrous acid (HONO) and nitric oxide (NO), is a key process of the global nitrogen (N) cycle and has significant implications for atmospheric chemistry. To understand the underlying mechanisms of soil N r emissions, air-dried or oven-dried soils are commonly used in the laboratory. To date, few studies have compared the effects of different drying methods on soil N r gas fluxes and N fractions. Here, the authors studied soil water content, pH, (in)organic N content, and N r gas fluxes of air-dried, freeze-dried, oven-dried, and fresh soils from different land-use types. The results showed that the soil pH of air-dried and oven-dried samples was significantly lower compared with fresh soil from farmland and grassland, but higher compared with forest soil. The difference in soil pH between freeze-dried and fresh soil (mean ± standard deviation: 0.52 ± 0.31) was the lowest. In general, all drying methods increased the soil NH 4 + -N, NO 3 − -N, and dissolved organic N contents compared with fresh soil (P < 0.05). The maximum HONO and NO flux and total emissions during a full wetting-drying cycle of fresh soil were also increased by air-drying and oven-drying (P < 0.001), but comparable with freeze-dried soil (P > 0.2). In conclusion, all drying methods should be considered for use in studies on the landatmosphere interface and biogeochemical N cycling, whereas the freeze-drying method might be better for studies involving the measurement of soil N r gas fluxes. 冷冻干燥更适合土壤活性氮气体 (HONO和NO) 排放的研究？摘要

Global and Regional Patterns of Soil Nitrous Acid Emissions and Their Acceleration of Rural Photochemical Reactions

“…The drying time took 6–12 hr. The mixing ratio of HONO in the headspace was determined by high‐performance liquid chromatography (HPLC, Agilent 1200, Agilent Technologies, Santa Clara, CA, USA) based on the derivatization of nitrite with sulfanilamide (SA) and N ‐(1‐naphthyl)‐ethylenediamine dihydrochloride (NED) under acidic conditions (Huang et al., 2002; Wu et al., 2020). The time resolution was ∼6 min, and the lower detection limit was ∼4 ppt for HONO.…”

An investigation into atmospheric nitrous acid (HONO) processes in South Korea

“…Emissions from soil bacterial activity are important sources of HONO. The amount of their emissions depends on the soil type, land category, fertilization, temperature, soil water content (SWC in %), and soil pH (Meusel et al, 2018;Wu et al, 2020). In this study, HONO emissions were estimated based on the ratio of HONO to NOx emissions from soil (Oswald et al, 2013).…”

Addressing nitrogenous gases from croplands toward low-emission agriculture

“…HONO, a precursor of the hydroxyl radical, plays important roles in tropospheric chemistry, human health risk (could damage the respiratory system), and indoor air quality. Wu, et al 78 noticed that soil reactive nitrogen gas (including HONO) emissions are mainly driven by nitrification and denitrification, which are highly relevant to soil pH, inorganic N content, and microbiological mechanisms. Despite these available studies, a large unknown source of atmospheric HONO (especially during the daytime) 79 and the complex biogeochemical reactions for soil HONO emissions are still not clearly elucidated.…”