Acidified potassium iodide reduction method: A rapid and precise method for measuring microbial nitrification rate across environments
ID:777 Poster Presentation

2025-01-14 22:05 (China Standard Time)

Session:Session 3-The Nitrogen Cycle Towards a Sustainable Ocean: From Microbes to Global Biogeochemistry

Abstract
Developing an accurate and well-established method for measuring nitrification rate is important to understand the role of nitrification process in the nitrogen cycle across environments. Here, we present a rapid and more accurate method to determine the ammonia oxidation rate (Ra) and the nitrite oxidation rate (Rn) simultaneously using stable isotope tracing and acidified potassium iodide reduction (SIT-APIR). 15NH4+ was added to the incubation as a tracer to measure the Ra by calculating produced 15NO2- and 15NO3-, while 15NO2 was used as another tracer for Rn determination by calculating produced 15NO3-. The produced 15NO2- and 15NO3- were chemically reduced to 31NO with potassium iodide (KI) and zinc-cadmium reducing agent couple with KI, respectively. High throughput measurements of 31NO were achieved by a membrane inlet mass spectrometer (MIMS). Based on the optimized reaction conditions, an improved method with lower detection limit (0.1 μmol L-1), higher precision (relative error: 4.39% for 15NO2-, 0.65% for 15NO3-) and stable (relative standard deviation: 3.12% for 15NO2-, 8.97% for 15NO3-) was developed to quantify the concentrations of 15NO2- (0.1-200 μmol L-1) and 15NO3- (0.1-80 μmol L-1) with excellent calibration curves (R2≥0.994). In addition to water and sediment samples, this method can be widely applied to determine the Ra and Rn of dry soil. Overall, this SIT-APIR method provide a precise, fast, and promising approach for determining Ra and Rn in the environment with low cost.

 
Keywords
isotope tracing, potassium iodide reduction, membrane inlet mass spectrometer, ammonia oxidation rate, nitrite oxidation rate
Speaker
Yuexi Ma
Master, Guangzhou University

Author
Yuexi Ma Guangzhou University
Jiapeng Wu Guangzhou University
xiaoyi Li Guangzhou University
Yiguo Hong Institue of Environmental Research at Greater Bay; GuangZhou University