Publications
NIBIOs employees contribute to several hundred scientific articles and research reports every year. You can browse or search in our collection which contains references and links to these publications as well as other research and dissemination activities. The collection is continously updated with new and historical material.
2000
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Authors
Jan Mulder J.F. Gallardo Lancho E. Matzner Edward Tipping Charlotte Bryant Nicholas Clarke S. Lofts B. Michalzik A. Vicente EstebanAbstract
No abstract has been registered
Abstract
Nitrogen is among the most important plant nutrients, and the effects on forest trees of changes in the concentrations and fluxes of both inorganic and organic nitrogen need to be known. In Norway, much of the nitrogen present in natural waters is organic (Mulder et al., 2000), therefore this fraction can not be neglected. Work using glycine has shown that forest plants can take up some forms of organic nitrogen directly, without preliminary mineralisation (Nsholm et al., 1998).Amino acids and amino sugars appear to be the most important organic sources of nitrogen for plants, including Norway spruce (Picea abies (L.) Karst.) (Johnsson et al., 1999). Organic nitrogen occurs in different forms. In soils, the most important are heterocyclic compounds and amino acids (35 % and 40 % respectively, Schulten and Schnitzer, 1998). In soil waters, amino sugars may also be important (Michalzik and Matzner, 1999).At present, organic nitrogen is normally determined as the difference between total nitrogen and the sum of nitrogen in nitrate and ammonium. This is not entirely satisfactory, as there will be a certain amount of uncertainty in each of the three determinations required. The total uncertainty involved in the determination of organic nitrogen may then be quite large compared to the actual concentration, especially when most nitrogen is present as inorganic nitrogen.A method for the direct determination of organic nitrogen is therefore desirable. Because organic nitrogen generally has a higher molecular weight than inorganic nitrogen, it might be possible to separate organic from inorganic nitrogen using size fractionation methods. In 1998, we worked on the setting up of methods for the determination of amino acids and amino sugars in soil waters, and on the direct determination of organic nitrogen using equilibrium dialysis.
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1999
Authors
Mehreteab TesfaiAbstract
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Authors
Jan Mulder J.F. Gallardo E. Matzner Edward Tipping Charlotte Bryant Nicholas Clarke S. Lofts B. Michalzik M.A. VicenteAbstract
No abstract has been registered
Abstract
DOC concentrations in soil water in podzols decreased from median values of 37 and 39 mg/l in the F and H layers, respectively, to about 6 mg/l in the B horizon. The decrease was most pronounced in the mineral soil. An increase in concentrations was found in the surface soils in late summer and autumn, apparently due in large part to increased production, which took place in both the canopy and the forest floor, although evaporative concentration of soil water could also have been partially responsible. In the B horizon, increased concentrations of DOC could be observed in the autumn, although these increases were much lower than for the surface horizons. A correlation was found between the surface soil DOC concentrations and the mean surface soil temperature 1 to 2 months previously, which could be due to the buffering effect of sorption processes. However, the increase in the net amount leached could not be clearly attributed to increased temperature. In the autumn, concentrations did not decline immediately when temperature decreased, which may be due to leaching of previously adsorbed organic matter. During the autumn, concentrations of DOC in streams increased in periods of high discharge due to increased input of high-DOC surface soil water. At the same time, DOC concentrations in surface soil water largely decreased, presumably as DOC was washed out. An increase in DOC was not seen in periods of high discharge in the early spring. The highest concentrations of TOC (both with and without flux-weighting) at the weir were also found in the autumn). Correlation of TOC in streamwater with temperature was poor but, for the winter months, often significant. A positive correlation in the winter was probably associated with higher fluxes due to temperature-induced snowmelt. DON, which is the dominant form of dissolved nitrogen at all depths in the podzols at Birkenes, also decreased sharply in concentration in the mineral soil. However, there was an increase in the concentration of DON relative to DOC. The C/N ratio thus decreased downwards in the soil, indicating a possible preferential adsorption of N-poor DOC. Much of the DON in throughfall appeared to be of low molecular weight. This was not the case for DON in soil water.
1998
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No abstract has been registered