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.
2006
Authors
Aksel GranhusAbstract
No abstract has been registered
Authors
Aksel GranhusAbstract
No abstract has been registered
Authors
Paal KrokeneAbstract
Bark beetles and associated phytopathogenic fungi elicit defence responses in conifers that may interfere with beetle establishment and development. Norway spruce is serving as a useful model species for studies of induced defences elicited by beetle attacks, fungal inoculation, and treatment with chemical elicitors.When trees are pretreated with a sublethal dose of fungal inoculations or with the phytohormone methyl jasmonate they become much more resistant to subsequent bark beetle attacks or artificial mass inoculations with fungi. This induced disease resistance follows dose-response dynamics, is nonspecific with respect to the pretreatment organism, appears to be nonsystemic, takes weeks rather than days to become activated, and can also be activated by mechanical wounding alone.Application of methyl jasmonate to Norway spruce stems induces a massive increase in terpene levels and external resin flow on the stem, whereas no increase is observed in soluble phenolics. Methyl jasmonate-application also leads to significantly less bark beetle colonization, with shorter parental galleries and fewer eggs laid in treated bark. There were also reductions in the number of beetles produced and the mean dry weight per beetle in methyl jasmonate-treated bark. Furthermore, fewer beetles were attracted to conspecifics tunneling in MJ-treated bark.The exact mechanisms responsible for induced resistance in Norway spruce and other conifers have not been determined, but inducible anatomical defense responses such as changes in polyphenol-containing parenchyma cells (PP cells) in the phloem and induction of traumatic resin duct formation in the sapwood seem to play an important role.
Authors
Seppo NevalainenAbstract
No abstract has been registered
Authors
Tor J. JohansenAbstract
No abstract has been registered
Authors
Tor J. JohansenAbstract
No abstract has been registered
Abstract
Detailed analyses of thresholded ecological interactions can improve our understanding of the transition from aperiodic to periodic dynamics. We develop a threshold model of the population dynamics of outbreaking bark beetle populations that alternate between non-epidemic and epidemic behavior. The model involves accumulation of resources during low-density periods and depletion during outbreaks. The transition between the two regimes is caused by disturbance events in the form of major tree felling by wind. The model is analyzed with particular reference to the population dynamics of the spruce bark beetle (Ips typographus) in Scandinavia for which a comprehensive literature allows full parameterization. The fairly constant outbreak lengths and the highly variable waiting time between outbreaks that are seen in the historical records of this species agree well with the predictions of the model. The thresholded resource-depletion dynamics result in substantial variation in the degree of periodicity between stochastic realizations. The completely aperiodic tree colonizations are partly predictable when the timing of the irregular windfall events are known. However, the predictability of inter-outbreak periods is low due to the large variation of cases falling most frequently in the middle between the extremes of purely nonperiodic (erratic) and periodic (cyclic) fluctuations.
Abstract
Toxic effects of aluminium (Al) on Picea abies (L.) Karst. (Norway spruce) trees are well documented in laboratory-scale experiments, but field-based evidence is scarce. This paper presents results on fine root growth and chemistry from a field manipulation experiment in a P. abies stand that was 45 years old when the experiment started in 1996. Different amounts of dissolved aluminium were added as AlCl3 by means of periodic irrigation during the growing season in the period 19972002. Potentially toxic concentrations of Al in the soil solution were obtained. Fine roots were studied from direct cores (1996) and sequential root ingrowth cores (1999, 2001, 2002) in the mineral soil (040 cm). We tested two hypotheses: (1) elevated concentration of Al in the root zone leads to significant changes in root biomass, partitioning into fine, coarse, living or dead fractions, and distribution with depth; (2) elevated Al concentration leads to a noticeable uptake of Al and reduced uptake of Ca and Mg; this results in Ca and Mg depletion in roots. Hypothesis 1 was only marginally supported, as just a few significant treatment effects on biomass were found. Hypothesis 2 was supported in part; Al addition led to increased root concentrations of Al in 1999 and 2002 and reduced Mg/Al in 1999. Comparison of roots from subsequent root samplings showed a decrease in Al and S over time. The results illustrated that 7 years of elevated Altot concentrations in the soil solution up to 200 M are not likely to affect root growth. We also discuss possible improvements of the experimental approach.
Abstract
Conidia germination of the root pathogen fungi Fusarium sp. and Cylindrocarpon sp. were followed for up to 96 hours in the presence of border cells from newly germinated Norway spruce. The border cells stimulated the conidium germination of both fungi. We postulate that this may be a part of the defence mechanism of Norway spruce against pathogens. The stimulating agent is unknown The stimulating effect was not seen when border cells originated from plants grown in the presence of aluminium
Abstract
No abstract has been registered