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.
1997
Authors
A. Tietema C. Beier P. H. B. deVisser B. A. Emmett P. Gundersen O. Janne Kjønaas C. J. KoopmansAbstract
No abstract has been registered
Authors
Albert Tietema C. Beier P.H.B. de Visser Bridget A. Emmett Per Gundersen O. Janne Kjønaas Chris J. KoopmansAbstract
The results of two European fieldscale manipulation projects (NITREX and EXMAN) were used to evaluate the effect of ecosystem disturbance on nitrate leaching in coniferous forest ecosystems. The first principle component (PC1) of a principle component analysis explained 85% of the variation in nitrate leaching between the 12 sites. This PC1 consisted of nitrogen concentrations and fluxes in the ecosystem, and was interpreted as an indicator of N status.Nitrate leaching responded rapidly to manipulation of nitrogen deposition, especially in sites with ambient high nitrate leaching. This rapid response could be explained partly by an immediate hydrological response of increased drainage. However, results of field-scale 15N tracer experiments indicated that microbial processes in the organic layer had changed after a few years of changed N deposition. In sites with already significant nitrate leaching, irrigation caused a large increase in nitrate leaching due to enhanced mineralization. Combined fertilization and irrigation had only a limited effect on nitrate leaching in nitrogen-limited sites, whereas in nitrogen-saturated sites, nitrate leaching was significantly increased.The hypothesized nitrate pulse as a result of rewetting after drought, did not occur in any of the sites. We conclude that the effect of disturbance on nitrate leaching depends on the N status of the ecosystem: in sites that are nitrogen-saturated, nitrate leaching is very sensitive to disturbance
Authors
Jan Mulder Petter Nilsen Arne Olav Stuanes Magne HuseAbstract
No abstract has been registered
Authors
O. Janne Kjønaas Arne Olav StuanesAbstract
No abstract has been registered
Authors
Birger SolbergAbstract
No abstract has been registered
Authors
Finn Roll-Hansen Richard Horntvedt Helga Roll-HansenAbstract
No abstract has been registered
Authors
Jarmo Poikolainen E. KubinAbstract
No abstract has been registered
Abstract
Fungi were isolated from the beetles, Ips typographus f. japonicus and Yezo spruce (Picea jezoensis) trees infested with the beetles in Hokkaido, Japan. Nine species of ophiostomatoid fungi including one new species were identied. They were Ceratocystiopsis minuta, Ceratocystis polonica, Ophiostoma ainoae, O. bicolor, O. cucullatum, O. europhioides, O. penicillatum, O. piceae, and a new species described here as O. japonicum. Based on frequencies of occurrence, O. ainoae, O. bicolor, O. penicillatum, and O. piceae were regarded as dominant associates of I. typographus japonicus, and C. minuta, C. polonica, O. europhinoides, and O. japonicum were subdominant. The species of ophiostomatoid fungi associated with I. typographus japonicus in Japan are almost identical to those associated with I. typographus infesting Norway spruce (P. abies) in Europe. This study improves our knowledge of the biogeography of the ophiostomatoid fungi and the insects with which they are associated.
Abstract
No abstract has been registered
Abstract
Pole-size Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) were inoculated with two fungi (Ophiostoma pseudotsugae (Rumb.) von Arx and Leptographium abietinum (Peck) Wingf.) associated with the Douglas-fir beetle (Dendroctonus pseudotsugae Hopkins) to evaluate their pathogenicity. Pruning the lowermost 30% of the live crown had no effect on host tree defenses. Inoculation with O. pseudotsugae produced significantly longer lesions in the phloem and resulted in a significantly greater percentage of necrotic phloem than inoculation with L. abietinum. The percentage of occluded sapwood was also greater following O. pseudotsugae inoculations, but the difference was not statistically significant. Individual lesion lengths declined significantly with increasing inoculation density, but the total percentage of necrotic phloem increased significantly. Both fungi appeared to be better adapted to grow in sapwood than in phloem. None of the inoculated trees were dead after 5 months, but some were chlorotic with less than 30% functional sapwood within the inoculation band. The results suggest that these fungi may assist the Douglas-fir beetle in overcoming the defenses of live trees.