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.
1993
Forfattere
Richard HorntvedtSammendrag
No abstract has been registered
Sammendrag
No abstract has been registered
Sammendrag
No abstract has been registered
Forfattere
Erik Christiansen Gunnar FjoneSammendrag
Defoliation of conifers occasionally precedes bark beetle attacks, suggesting that a severe loss of foliage and ensuing reductions in carbohydrate availability may enhance host tree susceptibility. To shed light on this question, different degrees of defoliation on young Picea abies were simulated by removing whole whorls of branches from below, the trees retaining 100, 50, or 25% of their original crown biomass. After one week or one year, the trees were inoculated with Ophiostoma polonkum, a tree-killing fungus transmitted by Ips typographus. Fungal proliferation and tree mortality increased with increasing levels of pruning. Pruning reduced stem diameter growth, but not carbohydrate reserves in foliage and bark. Foliar N, P, and Ca increased with increasing pruning. The results lend support to the hypothesis that a reduction in the photosynthesis capacity increases host tree susceptibility to a beetle-fungus attack, and that induced defence against infection depends on efficient translocation of assimilates to the sites of infection.
Forfattere
Per Holm NygaardSammendrag
No abstract has been registered
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Mette Goul ThomsenSammendrag
No abstract has been registered
Forfattere
Harald Kvaalen Arild ErnstsenSammendrag
It is known that reducing the partial pressure of O2 influences the induction of somatic embryogenesis. We tested the hypothesis that O2 causes changes in the endogenous levels of exogenously supplied benzyladenine (BA) or 2,4-dichlorophenoxyacetic acid (2,4-D).Embryogenic tissue of Picea abies was incubated under reduced (2.5, 5 kPa) and ambient (21 kPa) levels of O2 for 1, 3, 7 and 11 days and the endogenous concentrations of BA and 2,4-D were measured. For all treatments the concentration of BA in the tissue increased until the third day. At day 3, the ratio of BA in the tissue relative to the initial concentration in the medium, was 3.9, 2.8 and 1.9 for tissue incubated under 2.5, 5 and 21 kPa O2, respectively. The BA concentration then declined gradually. Uptake of 2,4-D was inhibited at low O2 levels.However, 2,4-D gradually accumulated in tissue grown under hypoxia, so that high levels were reached by day 11. These shifts in the BA and 2,4-D levels also caused a transient increase in the BA to 2,4-D ratio in tissue incubated under hypoxia. Although relevant for the previously reported effects of oxygen on induction of embryogenic tissue, it is unlikely that oxygen-induced alterations in BA and 2,4-D levels alone suffice to explain these findings.
Forfattere
Dan AamlidSammendrag
No abstract has been registered
Forfattere
Dan AamlidSammendrag
No abstract has been registered
Forfattere
Oddvar SkreSammendrag
The measurements were carried out on excised leaf discs and intactplants by infrared gas analyser technique. The sample plants had been grown for six weeks in varying temperature, light and daylengths. The photorespiration was estimated from measurements at low oxygen level. A strong temperature acclimation effect was found on CO2 exchange rates. Long term low-temperature treatment caused a reduction in photosynthesis and its temperature optimum in all birch populations. Strong acclimation effects of light were also found. Short term (48 hours) low-temperature treatment reduced photosynthesis rates at low light levels. Mountain birch from northern or arctic populations showed relatively high net photosynthetic rates compared with southern populations.