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.
2004
Abstract
The process of model building in the environmental sciences and when dealing with ecosystems is discussed. Two types of modeling approaches need to be distinguished: An algorithmic one, which has been used traditionally in physics, meteorology, and other branches where biological degrees of freedom are either absent or neglectable; and an interactive one, which is a new framework in computer science and seems to be most suitable in cases where organisms (including humans) as agents in ecosystems are to be taken into account. The first modeling approach is exemplified by state models in dynamic systems theory and expresses the correspondence imposed by Natural Law between inferential entailment in a formal system and causal entailment in natural systems. Modeling is to be separated from simulation. Simulation is a less restrictive type of modeling in which the description of non-interactive behaviour is the purpose and no constraints on the correspondence to internal states are imposed. The second (new) modeling approach is exemplified by interactive simulation models. It is able to express the correspondence in behaviour imposed by engineering standards (or cultural norms in general) between documentation, training and application in interactive choice situations such as games or ecosystem management. It generalises the notion of simulation for interactive problems. In an idealised situation the strictest correspondence between behaviour in a natural and a virtual system is expressed as bisimulation. The principles for model building are shortly demonstrated with examples.
Abstract
Dette sammendraget beskriver forekomsten av sharkavirus i Norge, både funnet av sharkavirus på Njøs i 1998 og kartleggingsarbeidet i årene 1998-2003.
Authors
Svein Solberg Kjell Andreassen Nicholas Clarke Kjetil Tørseth Ole Einar Tveito Geir-Harald Strand Stein Michael TomterAbstract
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When conifers such as Picea abies (Norway spruce) are attacked by insects or pathogens, they often produce increased quantities of terpenoid oleoresin. This response can be mimicked in young P. abies seedlings by treatment with methyl jasmonate. In this study, we determined the effect of methyl jasmonate on the terpenoids and other chemical defenses of mature P. abies, and investigated if this treatment protected trees against attack by the blue-stain fungus Ceratocystis polonica, the most important fungal associate of the bark beetle Ips typographus. Methyl jasmonate treatment induced the formation of traumatic resin ducts in the developing xylem, enhanced resin flow, and stimulated increased accumulation of monoterpenes, sesquiterpenes, and diterpene resin acids. However, almost no significant changes in terpene composition were detected. In addition, no changes in soluble phenolic content were observed. There was a very high variability both among and within clones in the timing and degree of response to methyl jasmonate. These chemical and anatomical changes were correlated with increased resistance to C. polonica, suggesting that terpenoid oleoresin may function in defense against this pathogen.
Authors
Alhaji S. JengAbstract
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The forest stand growth simulator TRAGIC (tree response to acidification in groundwater in C) which has been developed to serve as a decision support system and a visualisation tool for scientists and forestry practitioners is introduced. TRAGIC places an emphasis upon visualisation techniques while at the same time providing detailed information on tree physiology and related parameters. The model is calibrated numerically to growth history data from two different European sites.Next, due to the importance of the visual component of the model, its ability to reproduce forest stand spatial structure is investigated, using an application of the theory of marked point processes. This analysis is applied to different experimental data sets for stands of different age, revealing information on planting schemes and the extent of significant spatial correlations.The spatial structure of the two model calibrations is then explored with the same methods. The point process analysis turns out to be a powerful diagnostic for model quality assessments, since spatial distribution is an indirect result of competition between trees for light.
Authors
Amy M. Brunner Igor A. Yakovlev Steven H. StraussAbstract
Background Real-time reverse transcription PCR (RT-PCR) has greatly improved the ease and sensitivity of quantitative gene expression studies. However, accurate measurement of gene expression with this method relies on the choice of a valid reference for data normalization. Studies rarely verify that gene expression levels for reference genes are adequately consistent among the samples used, nor compare alternative genes to assess which are most reliable for the experimental conditions analyzed. Results Using real-time RT-PCR to study the expression of 10 poplar (genus Populus) housekeeping genes, we demonstrate a simple method for determining the degree of stability of gene expression over a set of experimental conditions. Based on a traditional method for analyzing the stability of varieties in plant breeding, it defines measures of gene expression stability from analysis of variance (ANOVA) and linear regression. We found that the potential internal control genes differed widely in their expression stability over the different tissues, developmental stages and environmental conditions studied. ConclusionOur results support that quantitative comparisons of candidate reference genes are an important part of real-time RT-PCR studies that seek to precisely evaluate variation in gene expression. The method we demonstrated facilitates statistical and graphical evaluation of gene expression stability. Selection of the best reference gene for a given set of experimental conditions should enable detection of biologically significant changes in gene expression that are too small to be revealed by less precise methods, or when highly variable reference genes are unknowingly used in real-time RT-PCR experiments.