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.
2015
Abstract
Ten saplings of European ash (Fraxinus excelsior L.) naturally infected by the invasive ash dieback pathogen Hymenoscyphus fraxineus were collected in Ukraine and Norway and examined for bark necrosis and extension of discoloration in sapwood and pith in a stem region. Tissue-specific colonization profiles were determined by spatial analyses of symptomatic and visually healthy stem tissues using a H. fraxineus-specific qPCR assay and light microscopy. Our data suggest that hyphal growth in the starch-rich perimedullary pith is of particular importance for both axial and radial spread of H. fraxineus, but that most of its biomass accumulates in sapwood parenchyma. The study confirms the results from earlier work and presents new information that refines the current stem invasion model.
Authors
O. Janne Kjønaas Nicholas Clarke Toril Drabløs Eldhuset Ari Hietala Hugh Cross Kjersti Holt Hanssen Tonje Økland Holger Lange Jørn-Frode Nordbakken Ingvald RøsbergAbstract
No abstract has been registered
Authors
O. Janne Kjønaas Nicholas Clarke Toril Drabløs Eldhuset Ari Hietala Hugh Cross Kjersti Holt Hanssen Tonje Økland Holger Lange Jørn-Frode Nordbakken Ingvald RøsbergAbstract
Tree harvest and different harvesting methods may affect the soil carbon (C) pool in forest ecosystems. In con- ventional stem-only timber harvesting (SOH), branches and tops that are left in the forests may contribute to the build-up of the soil carbon pool. In whole-tree harvesting (WTH), inputs of organic matter from branches and tops are strongly reduced. We established field experiments at Gaupen, SE and Vindberg, SW Norway, to study the short-term effects of SOH and WTH on processes affecting the accumulation and loss of soil C. Logging residues on the WTH plots were collected in piles that were removed after 6 months, rendering two sub treatments (WTH- pile and WTH-removal areas). We weighed selected trees and logging residues, surveyed understorey biomass production, quantified pre-harvest soil C and nutrient pools down to 30 cm. Soil respiration was measured and soil water sampled monthly during the growing season, while temperature and moisture were measured continuously. Organic and mineral horizons were incubated at different temperatures to estimate potential C and N mineraliza- tion, and deep sequencing of the ITS2 barcode region of fungal DNA was performed on the samples. Litterbags were deployed in the SOH plots. The logging residues amounted to 2.2-2.4 kg C m-2 At Gaupen, the mean in situ soil respiration rates increased following harvest with all treatments, but were significantly higher in WTH-pile and SOH relative to the WTH- removal areas in the first year as well as the fourth year of treatment. The former rates included aboveground decomposing needles and twigs but excluded coarser branches. The observed increase in the WTH-removal areas may be related to decomposing roots, as well as to increased C mineralization partly due to the higher soil tem- peratures following harvest. Soil temperature was the single most important factor explaining the variability in soil respiration rates over all treatments. At Vindberg, a decrease in soil respiration was observed with all treatments in the second and third years following harvest. At both sites, decomposition of logging residues from needles was more rapid relative to twigs and fine roots. The decomposing residues released a substantial amount of nitrogen which was gradually reflected in the soil water at 30 cm soil depth. A considerable increase in the NO3-N concen- tration also in the WTH-removal areas in the second year following harvest suggests an increase in N availability from decomposing fine roots and/or soil organic matter. The increased N availability in the WTH-removal areas was supported by results from short term lab incubations of undisturbed soil from the forest floor. The changes in the WTH-removal areas were also reflected in the soil fungal diversity: saprophytic ascomycetes on decaying plant material showed a striking increase in all treatments. For the WTH-removal areas, this may, again, be related to the increased input of root litter; however, the decrease in mycorrhizal basidiomycete species and the vigorous increase of ascomycetes following harvest may also affect the C mineralization of soil organic matter.
2014
Authors
Ari HietalaAbstract
No abstract has been registered
Abstract
No abstract has been registered
Authors
Ari HietalaAbstract
Polymerase chain reaction (PCR), a biochemical technology that generates copies of a particular DNA sequence, has revolutionized life sciences. Thirty years after its development in 1983, PCR is a standard and indispensable technique in medical and biological research for a variety of applications. Compared to many other fields, novel PCR applications and sequencing platforms have been rather slowly adopted by research groups engaged in wood protection. Regarding laboratory and field experiments for testing the efficacy of wood treatments, this opinion article discusses the potential of 2nd generation PCR applications and sequencing platforms for profiling 1) the growth and activity of wood decay microbes upon feeding and detoxification of treated wood, and 2) for recording the successional changes that take place in microbial community along with progress of wood decay.
Abstract
No abstract has been registered
Authors
Nina Elisabeth Nagy Katarzyna Sikora Paal Krokene Ari Hietala Halvor Solheim Carl Gunnar FossdalAbstract
No abstract has been registered
Abstract
No abstract has been registered
Abstract
Ari M. Hietala, Volkmar Timmermann, Isabella Børja & Halvor Solheim Norwegian Forest and Landscape Institute. PO Box 115, 1431 Ås, Norway: ari.hietala@skogoglandskap.no Owing to the Gulf Stream, the northernmost European populations of several tree species are found in Norway. Common ash (Fraxinus excelsior), the only native ash species in Norway, is present in the lowlands in the southeastern part with continental climate and in southern and southwestern coastal regions with North Atlantic climate up to Central Norway. The current standing volume of ash in Norway is ca 3 mill m3 (broadleaved trees in total 220 mill m3). The first documentation of Ash Dieback (ADB) is from 2008 from a nursery in the southeastern part of the country. A survey later that year showed that dieback symptoms were present over a distance of nearly 400 km in the southeastern region. In addition to nurseries and forests, ADB symptoms were observed on roadside, alley, garden and park trees. Based on the presence of old ADB-like stem lesions detected in 2008, the pathogen must have arrived to Norway no later than 2006. In 2008, the Norwegian Food Safety Authority laid down regulations with the aim of preventing further spread of ADB. These regulations divide the country into quarantine, observation and infection-free zones, and prohibit the export of ash seedlings, seed and wood from the quarantine zone. Despite of these regulations, the disease spread rapidly along the western coast in the period between 2009 and 2013, and currently only the ash stands in Central Norway are free of the disease. The rapid spread of the disease in Norway is obviously due to airborne dispersal of pathogen ascospores. In our experimental stand in SE Norway the number of pathogen fruit bodies can be as high as 10,000 per m2 in the peak season, mid-July to mid-August. During the early morning hours the amount of pathogen ascospores at a diseased stand can exceed 100,000 ascospores per m3 air. The first symptoms of the disease, necrotic lesions on leaf blade and petiole, appear typically during the first two weeks of August in SE Norway. To observe long-term impacts of ADB, eight monitoring plots have been established in continental and North Atlantic climate zones. In SE Norway with the oldest disease history, above 60 % of the trees with a breast height diameter (BHD) below 12.5 cm have so far died or suffer from severe defoliation, 1/3 of the larger trees being affected to a similar degree. The proportions of healthy (no signs of defoliation) small and larger trees are 20% and 37%, respectively. In SW Norway with more recent disease history a similar trend is observed but the proportion of dead trees is still small. As a consequence of ADB, the Norwegian nurseries no longer grow ash seedlings. There are currently no practical control options for the disease in forestland. Several European countries have reported that even at heavily diseased ash stands there are often some ash trees that show little symptoms. This may be due to genetic variation between trees in disease resistance, a hypothesis that is currently being investigated in several European projects. Thus implementation of forest management practices that eliminate ash could have a negative effect as survival of the tree ultimately depends on selection of trees with increased disease resistance. Bibliography for Ari M. Hietala Ari M. Hietala is a Senior Forest Pathologist at the Norwegian Forest and Landscape Institute, which is a primarily government funded organisation providing scientific research and services to government, non-governmental and commercial organisations. He has worked with a range of fungal root and shoot diseases occurring on broadleaved trees and conifers indigenous to the Nordic countries. Ari and the rest of the group participate currently in several European consortia engaged in ash dieback research.