Early season dynamics of soil nitrogen fluxes in fertilized and unfertilized boreal forests

Author(s)
Erich Inselsbacher, Olusegun Ayodeji Oyewole, Torgny Nasholm
Abstract

The supply of soil nitrogen (N) for plant uptake largely controls plant growth and has a major impact on a wide range of biogeochemical processes in terrestrial ecosystems. The soil solution typically contains a large variety of N forms and recent evidence suggests that the share of amino acids to soil N fluxes dominates over inorganic N in boreal forest soils. In this study we applied a microdialysis technique to investigate in-situ induced diffusive fluxes across microdialysis membranes (F

MD) in fertilized and non-fertilized boreal forest sites in early spring, at the onset of plant growth. We studied temporal shifts of F

MD at short (minutes to hours) and prolonged time-scales (hours to days). We also estimated N pools in soil water and KCl extracts and critically evaluated the significance of results depending on the method chosen. Our results indicate that F

MD of boreal forest soil is dominated by amino acids in early spring and that growing roots should encounter the full range of organic and inorganic N forms in these soils. In contrast, soil water and KCl extracts were dominated by NH

4

+. Some amino acids displayed rapidly declining F

MD (<1h) possibly due to the rapid formation of a depletion zone near the membrane surface but the F

MD of most amino acids remained high and unchanged over extended periods of dialysis indicating that these soils provide a continuous supply of amino acids for root uptake. Forest fertilization with NH

4NO

3 led to a significant increase in F

MD of NO

3

- and NH

4

+, with F

MD of NH

4

+ but not of NO

3

- remaining high for prolonged time. A separate trial with addition of NO

3

- showed a significantly slower decline of F

MD in soils of previously fertilized forests compared to unfertilized forests, suggesting biological immobilization being a major cause of rapid decline of nitrate fluxes. Our results corroborate earlier studies suggesting amino acids to be a significant fraction of plant available N in boreal forests. They also suggest that, besides inorganic N, roots may encounter a wide spectrum of amino acids after intercepting new soil microsites and that most, but not all, amino acids may be constantly replenished at the root surface. Further, from our results we conclude that detailed insights into in-situ N dynamics of soils can be gained through microdialysis.

Organisation(s)
Department of Geography and Regional Research
External organisation(s)
Swedish University of Agricultural Sciences (SLU)
Journal
Soil Biology and Biochemistry
Volume
74
Pages
167-176
No. of pages
10
ISSN
0038-0717
DOI
https://doi.org/10.1016/j.soilbio.2014.03.012
Publication date
07-2014
Peer reviewed
Yes
Austrian Fields of Science 2012
507015 Regional research
Keywords
ASJC Scopus subject areas
Soil Science, Microbiology
Sustainable Development Goals
SDG 15 - Life on Land
Portal url
https://ucrisportal.univie.ac.at/en/publications/early-season-dynamics-of-soil-nitrogen-fluxes-in-fertilized-and-unfertilized-boreal-forests(255fc02f-d29c-4976-a286-718c714a6a4b).html