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.
2003
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Authors
Erik Jautris Joner C. LeyvalAbstract
Phytoremediation as a means of cleaning up polluted soils has gained popularity during the last decade due to its convenience and low costs of installation and maintenance. When the target pollutant is biodegradable, this technology exploits the stimulating effect that roots have on microbial processes and physical/chemical modifications in the rhizosphere.Among the microorganisms that affect rhizosphere processes, symbiotic fungi forming mycorrhizas induce a series of changes in plant physiology, nutrient availability and microbial composition that may determine the outcome of a phytoremediation attempt. Beyond the rhizosphere, mycorrhizal hyphae act as the roots of the roots, and may thus extend the rhizosphere into the bulk soil by creating a new interface of soil-plant interactions: the hyphosphere.We here discuss some of the recent results on phytoremediation of organic pollutants with emphasis on processes in the mycorrhizosphere, and highlight future research priorities
Authors
Fred Midtgaard Karl ThunesAbstract
Det har vært omfattende angrep i the Mountain Pine Ridge Forest Reserve, Belize, av barkbiller. Denne undersøkelsen viser at angrepene skyldes en ukjendt barbilleart med rask utviklingstid og meget rask spredning. Totalt ble 80% av reservatet angrepet før det ble stoppet. Metoder for overvåking og bekjempelse er beskrevet på engelsk og spansk. During the years from 1998 to 2002, heavy attacks by an unknown bark beetle species occurred in the Mountain Pine Ridge Forest Reserve, Belize. The species is described in this publication, and methods for monitoring and control of this, and related species, is described in English and Spanish.
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Fred Midtgaard Karl Hilding ThunesAbstract
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Authors
Rune H. Økland Knut Rydgren Tonje ØklandAbstract
Previous studies point at biogeographic (i.e. evolutionary and demographic) and ecological (i.e. habitat differentiation and disturbance) processes as the most important causes of spatial variation in species richness and species composition. We examined patterns of variation in similarity of vascular plant and bryophyte species composition among 150 1-m2 plots distributed semi-randomly over 11 Norwegian boreal swamp-forest localities that were species-rich islands in an otherwise species-poor forest landscape. For each plot, 53 environmental variables were recorded. By using CCA analyses, we found that c. 20% of the explainable variation in species composition was due to swamp-forest affiliation, in addition to the c. 35% that was due to environmental differences between swamp-forest localities. The unique component of the species composition of each swamp forest was also emphasised by analyses of floristic dissimilarity: plots were significantly more floristically dissimilar if situated in different than if situated in the same swamp forest, even after environmental differences had been corrected for. The lack of any significant relationship between floristic dissimilarity and geographical distance or swamp-forest area indicated that this pattern was not mainly due to demographic processes. We argue that the floristic distinctness of swamp forests, in particular those richer in species and soil nutrients, is due to a combination of factors among which randomness in establishment in infrequently occurring gaps ( ‘windows of opportunity’) are likely to be important. The unique combination of important determinants of the species composition found for boreal swamp forests supports the view that there exists a diversity of explanations for diversity and that these, to a large extent, are system- and/or area-specific.
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An individual-based agent model is presented which resembles aspects of natural evolution in ecosystems under selective pressure due to limited resources. The environmental conditions are determined by spatial and temporal variability of resource abundances.The agents have to choose between three different types of resources; the one consumed most during lifetime solely counts for the fitness of the individual agent. Simulation runs show that populations specialized in different resource types are mutually influencing each other under temporal variation of a single resource type.Mobility of agents in a locally heterogenous world enables recolonization after a population has starved to death. Wavelet analysis of the population time series reveals that some observed population dynamics show phenomena such as localized periodicities which cannot be explained by linear dependencies on the resource input dynamics.
Authors
Live S. Vestgarden O. Janne KjønaasAbstract
The objective of this study was to quantify the net potential N mineralisation and nitrification rates in mineral soils of two coniferous forest soils subjected to different N additions. One study site was located at Åmli (Pinus sylvestris L. forest), southern Norway and another at Gårdsjön (Picea abies forest), southwestern Sweden. Mineral soil was collected from 14 to 19 and 24 to 29 cm depth in May at Gårdsjön and in May, July, September and November at Åmli. The soil was incubated in the dark at 15 °C for 2 months in the laboratory, and the NH4+ and NO3- content were compared relative to pre-incubated values. The initial contents of NO3- and NH4+ in the soil at the two sites were of about the same magnitude, but the potential net N mineralisation, ammonification and nitrification rates differed significantly. At Gårdsjön, the net N mineralistion ranged from 6 to 29 mg N kg-1 per 2 months, whereas a net N immobilisation generally occurred at Åmli. Additions of 0–50 kg N ha-1 per year had no effect on the transformation rates at the two sites. Applications of large single doses of 90 kg N ha-1 per year during the last 8 years have significantly increased the net nitrification rate in the soil at Åmli. However, a net N mineralisation was only observed in the soil 1 month after the N addition. At low N input levels, site-specific factors, such as the content of organic matter, clay, and moisture, seemed to a large degree to determine the transformation rates. Large spatial variability both within catchments and between catchments at Gårdsjön may have obscured the effects of small N inputs.
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Authors
Petter NilsenAbstract
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