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
Authors
Seif S. Madoffe Alf Bakke J.A. TarimoAbstract
No abstract has been registered
Authors
Bent Braskerud Helge Lundekvam Tore KrogstadAbstract
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Authors
Dale W. Johnson Trine Aulstad Sogn Sheila KvindeslandAbstract
The nutrient cycling model (NuCM) is a stand level model that depicts the cycling of N, P, K, Ca, Mg, and S on daily, weekly or monthly time scales. NuCM has been applied to several forest ecosystems (ponderosa pine, red spruce, beech, eastern deciduous, loblolly pine, slash pine, Scots pine, and Norway spruce) to simulate the effects of changing atmospheric deposition, harvesting, species change, precipitation quantity, increased temperature, elevated CO2, and liming. In some cases (e.g., harvesting, liming), the model output has matched field data quite well; however, it cannot be known whether the model does so because it accurately portrays nutrient cycling processes or simply because of chance. In other cases, NuCM simulations have either failed to match field data (as in the case of the observed chromatographic response of soil solution cations to a nitrate pulse in a beech forest) or produced results that are counterintuitive but as yet untested (as in the case where increased N translocation caused increased leaching). In that the primary purpose of these simulations has been heuristic rather than predictive, the simulation outputs that are either inconsistent with field data or counter-intuitive are of greatest interest. This review of NuCM applications led to the conclusion that the model has been more successful in matching decadal-scale changes in nutrient pools and soils and less successful in capturing intra-annual variations in soil solution chemistry. The NuCM model, like all models, can use improvements and these have been suggested; however, the model as it is has provided valuable insights into nutrient cycling in forest ecosystems, including the potential for short-term soil change and the great importance of nutrient translocation in N cycling.
Authors
Ola FlatenAbstract
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Tore SkrøppaAbstract
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Authors
Trygve Krekling Vincent R. Franceschi Alan A. Berryman Erik ChristiansenAbstract
A developmental and structural characterization of polyphenolic parenchyma cells (PP cells) in Norway spruce bark was undertaken as part of our studies on their role in defense against bark beetles and pathogenic fungi.PP cells form multiple circumferential layers of cells within the secondary phloem. A layer of PP cells begins differentiation at the start of each growth season, delineating an-nual growth increments in the secondary phloem. The PP cells grow in size over a number of years, and remain viable even in the oldest phloem layers of trees 100 years old.While most spruce clones examined had PP cell layers that are one cell thick, in one clone the PP cell layer is 2 cells thick with additional PP cells scattered throughout the intervening blocks of sieve cells. The additional cells develop from undifferentiated axial parenchyma cells during the first 5-8 years after formation of the PP cell layer.Division of PP cells in phloem layers older than 8 years give rise to additional PP cells. This accommodates the expansion of the stem circumference while maintaining the intactness of this defense barrier.The importance of phenolic accumulation is also indicated by examination of early stem development. PP cells are produced during the earliest stages of interfascicular cambium formation, and well organized layers are produced by the second year of growth. PP cells in all layers of 25 year old tree bark contained starch, lipids and polyphenolics, which changed in amount or character in a seasonal pattern.Plasmodesmata are abundant between adjacent PP cells and PP cells and ray parenchyma, where they are probably critical to nutrient and defense signal transport in the radial and axial directions. The formation of a new PP cell layer each season, the maintenance of the cells for many years, the early organization of this layer in the primary stem, and the dynamic physiological activity even older cells exhibit, supports
Authors
Sondre Skatter Bohumil KuceraAbstract
No abstract has been registered
Authors
Kåre Lye Mary Namaganda Halvor B. GjærumAbstract
No abstract has been registered