Probing soil nitrification and nitrate consumption using Δ17O of soil nitrate

In this study, we conducted both laboratory and field experiments to assess the use of Δ17O-NO3- for tracing soil nitrification and NO3− consumption. Soil samples spanning a wide range of physical and chemical properties were sampled from four sites for batch incubations and amendments with a Δ17O-enriched NO3− fertilizer. After amendments, the triple isotopes (δ15N, δ18O, and Δ17O) of soil NO3− were measured periodically and used in a developed Δ17O-based numerical model to simultaneously derive gross rates and isotope effects of soil nitrification and NO3− consumption. The measured Δ17O-NO3- was also used in the classical isotope dilution model to estimate gross NO3− turnover rates. In situ field soil sampling was conducted in a temperate upland meadow following snowmelt input of Δ17O-enriched atmospheric NO3− to assess the robustness of Δ17O-NO3- as a natural tracer. The results show that the temporal dynamics of Δ17O-NO3- can provide quantitative information on soil nitrification and NO3− consumption. In the laboratory incubations, a wide range of gross nitrification and NO3− consumption rates were estimated for the four soils using the Δ17O-based models. The estimated rates are well within the range reported in previous 15N tracer-based studies and not sensitive to oxygen isotopic fractionations during nitrification and NO3− consumption. Coupling Δ17O-NO3- with the dual NO3− isotopes using the numerical model placed strong constraints on t...
Source: Soil Biology and Biochemistry - Category: Biology Source Type: research