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2021

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Sammendrag

Information about forest background reflectance is needed for accurate biophysical parameter retrieval from forest canopies (overstory) with remote sensing. Separating under- and overstory signals would enable more accurate modeling of forest carbon and energy fluxes. We retrieved values of the normalized difference vegetation index (NDVI) of the forest understory with the multi-angular Moderate Resolution Imaging Spectroradiometer (MODIS) bidirectional reflectance distribution function (BRDF)/albedo data (gridded 500 m daily Collection 6 product), using a method originally developed for boreal forests. The forest floor background reflectance estimates from the MODIS data were compared with in situ understory reflectance measurements carried out at an extensive set of forest ecosystem experimental sites across Europe. The reflectance estimates from MODIS data were, hence, tested across diverse forest conditions and phenological phases during the growing season to examine their applicability for ecosystems other than boreal forests. Here we report that the method can deliver good retrievals, especially over different forest types with open canopies (low foliage cover). The performance of the method was found to be limited over forests with closed canopies (high foliage cover), where the signal from understory becomes too attenuated. The spatial heterogeneity of individual field sites and the limitations and documented quality of the MODIS BRDF product are shown to be important for the correct assessment and validation of the retrievals obtained with remote sensing.

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Sammendrag

Key words: VKM, risk assessment, Norwegian Scientific Committee for Food and Environment, Norwegian Food Safety Authority, biological control, Nematodes, Phasmarhabditis californica, Moraxella osloensis. Parasitic nematodes and associated bacteria are increasingly being used for biocontrol of molluscs. Functionally, it is the bacteria that kill and thus control the targeted pests, but the function of the bacteria is dependent on the nematodes, which should be regarded as vectors of biocontrol. Although the nematodes and the bacteria have a symbiotic relationship within such biocontrol formulations, it should be noted that they are not dependent on each other in the wild, but can establish separate populations which can be free-living or hosted by other organisms. The biocontrol product Nemaslug 2.0 contains the nematode Phasmarhabditis californica (strain P19D) and the bacterial symbiont Moraxella osloensis (unknown strain). The nematode was first described in 2016 and has never been reported in Norway. The lack of reports suggests that it is absent from Norway, but this conclusion comes with a high degree of uncertainty since there have been limited search efforts. The climatic thresholds of the nematode are not known, but its current distribution, spanning widely varying climates, suggests that it could survive and establish in Norway. Natural spread from currently known areas of establishment to natural habitats in Norway is ruled out due to the nematode’s limited dispersal capacity. However, human-assisted spread (e.g. via the use of biocontrol products) and establishment would be likely if Nemaslug 2.0 is allowed for use in open fields in Norway. Use of Nemaslug 2.0 in greenhouses and other enclosed areas is not likely to facilitate spread to natural habitats in Norway provided that residues are properly handled. However, deposition of product residues from greenhouses to outdoor areas may result in local establishment of the nematode in the vicinity of the deposition. Phasmarhabditis californica has a broad host range and may parasitize both rare/endangered and common mollusc species. However, there is no scientific evidence suggesting that the nematode can affect natural populations of molluscs in wild habitats, or otherwise have negative effects on biodiversity. The nematodes’ association with the bacteria Moraxella osloensis is most likely lost, or at least weakened, in natural habitats, suggesting that the nematode becomes less capable of killing its hosts in the wild. Phasmarhabditis californica is not capable of harming or infecting humans. The bacterial species Moraxella osloensis is already present in Norway in a few locations and at a low abundance, and it may be native to Norway. Little is known regarding its distribution in natural environments, but the literature shows that it can infect humans and other mammals. In humans with immunodeficiency or other comorbidities, M. osloensis can cause meningitis, vaginitis, sinusitis, bacteremia, endocarditis, and septic arthritis. The risk of infection in people handling Nemaslug 2.0 can probably be substantially reduced by protective clothing and appropriate handling. We are not aware of any reported health issues arising from use of the previous version of Nemaslug, which also contains M. osloensis. Different strains of M. osloensis are known to vary in their sensitivity to antibiotics, and likely in other traits too. Thus, the lack of information provided about the strain identity and specific characteristics of the strain used in Nemaslug 2.0 generates a high degree of uncertainty regarding its pathogenicity, climate tolerance, sensitivity to antibiotics etc.