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.
1998
Authors
Per Gundersen Bridget A. Emmett O. Janne Kjønaas Chris J. Koopmans Albert TietemaAbstract
Impact of nitrogen (N) deposition was studied by comparing N fluxes, N concentrations and N pool sizes in vegetation and soil in five coniferous forest stands at the NITREX sites: Grdsjn (GD), Sweden, Klosterhede (KH), Denmark, Aber (AB), Wales, UK, Speuld (SP), the Netherlands, and Ysselsteyn (YS), the Netherlands. The sites span a N- deposition gradient from 13 to 59 kg N ha-1 yr-1. Measurements of soil N transformation rates by laboratory and field incubations were part of the site comparison. Further, results from 4-5 yr of NH4NO3 addition (35 kg N ha-1 yr-1) at low deposition sites (GD, KH, AB) and 6 yr of N removal (roofs) at high deposition sites (SP, YS) were included in the analysis. Significant correlations were found between a range of variables including N concentrations in foliage and litter, soil N transformation rates and forest floor characteristics. Using the methods from principal component analysis (PCA) these variables were summarized to an index of site N status that assigned the lowest N status to GD and the highest to YS. Site N status increased with N deposition with the exception that AB was naturally rich in N. Nitrate leaching was significantly correlated with N status but not correlated with N deposition.Forest floor mass and root biomass decreased with increased N status. Characteristics of the mineral soil were not correlated with vegetation and forest floor variables. High C/N ratios in the mineral soil at the high-N deposition sites (SP, YS) suggest that the mineral soil pool changes slowly and need not change for N saturation to occur. Nitrogen transformation rates measured in laboratory incubations did not agree well with rates measured in the field except for a good correlation between gross mineralization in the laboratory and net mineralization in the field. The changes in N concentrations and fluxes after manipulation of N input followed the direction expected from the site comparison: increases at N addition and decreases at N removal sites. Nitrate leaching responded within the first year of treatment at all sites, whereas responses in vegetation and soil were delayed. Changes in N status by the manipulation treatments were small compared to the differences between sites. Changes in nitrate leaching were small at the low-N status sites and substantial at the high-N status sites. Nitrogen-limited and N-saturated forest ecosystems could be characterized quantitatively.
Authors
Øystein Austarå C. Carter Gudmundur Halldórsson Susanne Harding J. EilenbergAbstract
No abstract has been registered
Authors
Dag FjeldAbstract
No abstract has been registered
Authors
Erik Trømborg Birger SolbergAbstract
No abstract has been registered
Authors
Jan Stenlid K. Kammiovirta R. Karjalainen J.O. Karlsson Kari Korhonen Halvor Solheim Iben Margarethe ThomsenAbstract
No abstract has been registered
Authors
Halvor Solheim E. BjøreAbstract
No abstract has been registered
Abstract
No abstract has been registered
Authors
Tor MykingAbstract
No abstract has been registered
Authors
Martin Weih P. Staffan Karlsson Oddvar SkreAbstract
Intra-specific relationships between growth traits and nitrogen economy were studied for seedlings of mountain birch (Betula pubescens ssp. tortuosa) originating from three climatically different regions within the northern forest margin in subarctic Fennoscandia. The experiment was carried out using potted seedlings grown in Abisko, northern Sweden, through two complete growing seasons. The seedlings were grown in peat and assigned to two different temperature and fertilization treatments according to a factorial design. The treatments were ambient and ca. 2.5oC elevated temperature (passive greenhouse), and soil nutrient fertilization corresponding to 1 and 10 g nitrogen m-2 season-1. Significant differences among provenances were found in almost all growth and nitrogen economy traits studied. The differences in growth rate, which reached 47%, were explained primarily by leaf weight ratio (biomass allocation to leaves) and secondly by leaf area productivity (biomass production per unit leaf area). Both the nitrogen productivity and residence time of nitrogen (with respect to above-ground nitrogen losses) varied between provenances; no significant relationship was found between these two traits. Differences in residence time of nitrogen were more related to biomass loss ratio (leaf biomass losses per unit total plant biomass production) than to nitrogen concentration of abscised leaves. The intra-specific variation in nitrogen economy between mountain birch provenances is discussed with respect to the possibility of significant genotype x environment interaction.
Authors
Arne Olav Stuanes O. Janne KjønaasAbstract
Nitrogen has been added to a forested 0.52 ha headwater catchment (G2 NITREX) at Grdsjn, Sweden, to study the ecosystem response to elevated N deposition. The catchment is dominated by naturally regenerated, mixed-age conifers, mainly Norway spruce, with Scots pine dominating in dry areas. After a pre-treatment period of about 1 yr of soil solution sampling, N was added to the whole catchment as an NH4NO3 solution by means of sprinklers. Total N input as throughfall to the catchment increased from the ambient 13 kg N ha-1 yr-1 in the pre-treatment year to a total of about 50 kg N ha-1 yr-1 in the 4 treatment years. Soil solution was collected by tension lysimeters at 4 locations in G2 NITREX covering a moisture gradient from the dry upper to the lower wet parts of the catchment, at 2 locations in a nearby control catchment (F1 CONTROL), and at 2 locations in an adjacent catchment (G1 ROOF) at which ambient throughfall is excluded by a roof and replaced by unpolluted throughfall added by sprinklers. After 4 yr of N addition, the volume-weighted average NO3 concentrations in G2 NITREX were higher than the pre-treatment values. Concentrations showed a progressive increase over time. In the 2 first treatment years this increase occurred only in the rooting zone but during the second 2 treatment years a pronounced increase also came in deeper layers. The lack of these trends in the F1 CONTROL and G1 ROOF catchments precludes natural variations in climatic conditions as the main cause for this increase. Relative to inputs, NO3 concentrations in soil solution were low and showed large variations between the drier and wetter locations with peak concentrations in late fall and spring. Nitrate in soil solution generally constitutes less than 10% of the inorganic mobile anions and thereby contributes much less to the leaching of H, Al, and base cations than CI and SO4, the dominant mobile anions. Soil solution NH4 has not changed relative to the control and roof catchments. However, the system is changing. Increases in NO3 leaching indicate reduced immobilization of NO3 that can be due to episodic excess N supply of the microflora together with episodes of high waterflow.