The potential of using 15N natural abundance in changing ammonium-N and nitrate-N pools for studying in situ soil N transformations

  • Dianjie WangEmail author
  • Zhihong XuEmail author
  • Timothy J. Blumfield
  • Jacinta Zalucki
Soils, Sec 1 • Soil Organic Matter Dynamics and Nutrient Cycling • Research Article



This study examined the usefulness of 15N natural abundance (δ15N) with in situ core incubation to quantify the predominant N transformation processes in a natural suburban forest of subtropical Australia, which was subjected to prescribed burning.

Materials and methods

In situ core incubation for 3 days with 20 ml water, or 160.79 ml of 60 mg L1 NO3-N surface application, and in situ core with 160.79 ml water but without incubation were set up in Toohey forest for sampling three times as before (once) and after (twice) a prescribed burning. The δ15N of NH4+-N and NO3-N in the top 5 cm soil before and after the incubation, and δ15N of NO3-N in the 5–10 cm soil before incubation were compared with each other to examine the soil N mineralisation, nitrification, denitrification, and nitrate leaching processes.

Results and discussion

The significant decrease in δ15N of NH4+-N after incubation under 20 ml water treatment was ascribed to soil N mineralisation, and the significant decrease in δ15N of NH4+-N and significant increase in δ15N of NO3-N after incubation with elevated water and nitrate inputs were associated with N mineralisation and nitrification, respectively, 2 months after the burning. The 160.79 ml water treatment also triggered nitrification in the baseline soil cores in both samplings after the burning. Water was crucial to stimulate soil N mineralisation and nitrification, but excessive water depleted labile N pools and reduced N mineralisation and nitrification. Burning effects were hard to separate from the seasonal impacts on soil N cycling processes.


The δ15N in soil mineral N pools was sensitive to indicate soil N mineralisation and nitrification processes. Soil water and labile N were determining factors for N transformations in the soil. It is suggested that δ15N combined with soil inorganic N concentrations and net N transformation rates could be used to identify primary N transformation processes. More frequent samplings would be needed to differentiate burning impacts from the seasonal impacts on soil N cycling processes.


Field incubation Net N transformations δ15Soil water 



This study was completed with the support of postgraduate research scholarships from Griffith University; special thanks to Professor Weijin Wang of Griffith University for his help with the sample analyses and critical opinions in shaping this paper; thank Geoffrey Lambert for his assistance with the field works.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2020

Authors and Affiliations

  1. 1.Environmental Future Research Institute and School of Environment and ScienceGriffith UniversityBrisbaneAustralia
  2. 2.School of Geographical ScienceFujian Normal UniversityFuzhouChina

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