Dissolved soil organic nitrogen and carbon in a Norway spruce stand and an adjacent clear-cut |
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Authors: | A Smolander Veikko Kitunen Eino Mälkönen |
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Institution: | (1) Finnish Forest Research Institute, Vantaa Research Centre, P.O. Box 18, 00131 Vantaa, Finland e-mail: Aino.Smolander@ Metla.Fi Tel.: +358-9-857051 Fax: +358-9-8572575, FI |
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Abstract: | The aims of this study were to characterize dissolved soil organic N (DON) and C (DOC) in a coniferous stand and an adjacent
clear-cut, and to evaluate the importance of DON in N leaching. The study was carried out in a Norway spruce stand and a clear-cutting
treatment in the same forest stand. Concentrations of DON in soil solution were monitored for 5 years after clear-cutting
with gravity lysimeters. In the Norway spruce stand DON comprised 62–83% of the total N in soil solution over the 5-year period.
The concentrations of DON in the clear-cut were higher than in the forest stand, but the proportion of total N was lower.
To characterize dissolved organic matter, soil samples were aerobically incubated for 6 weeks in the laboratory, and the quantity,
molecular size distribution and chemical nature of both DON and DOC were determined from water extracts made before and after
the incubation. In the soil samples from the Norway spruce stand, C-rich compounds with a high C/N ratio and large molecular
size were formed. In contrast, after the incubation the major carriers of DON in soil samples from the clear-cut were N-rich
organic compounds with a low C/N ratio and a small molecular size. The distribution of different chemical fractions of DOC
in soil did not differ much whether recovered from the Norway spruce stand or the clear-cut. It was (from highest to lowest
concentration): hydrophobic acids>hydrophilic acids>phenols>hydrophilic neutrals. A major part of DON was also carried by
these fractions. During incubation the concentration of N-containing hydrophilic acids increased, especially in the soil from
the clearcut. In soil samples from the Norway spruce stand, the rate of net N mineralization was low and no NO3 was formed, whilst the rate of net N mineralization was high and net nitrification was intensive in soil from the clear-cut.
Received: 12 June 2000 |
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Keywords: | Clear-cutting Dissolved organic carbon Dissolved organic nitrogen Forest soil Nitrogen transformations |
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