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.
1999
Authors
Anatoly PisarenkoAbstract
No abstract has been registered
Authors
Carl Gunnar FossdalAbstract
Plants are exposed to a great number of microorganisms under natural conditions. Pathogenic fungi and oomycetes are the main factors contributing to plant diseases, thus further understanding of plant-pathogen interactions may provide information leading to new strategies for reducing the damage caused by these pathogens on economically important trees and crops. Active plant-responses to microorganisms differ with respect to the degree of responses and with respect to the outcome of the interaction. In response to pathogens, active plant-defenses can be induced. Both local and systemic plant defense-response may be induced by pathogens. This thesis present indications of both local and systemic host responses at the molecular and cellular levels, using the conifer Norway spruce as a model host to study plan-pathogen interactions. Norway spruce seedlings were infected separately with the pathogenic fungi Heterobasidion annosum and Ceratocystis polonica, the pathogenic oomycete Pythium dimorphum and the ectomycorrhizal fungus Laccaria bicolor, to study the local and systemic effects of the infections at the cellular and molecular level. Increased levels of lignification was seen within 2 to 4 days in response to the pathogens, and indications of cytoplasmic translocations were also observed as a response to hyphae invading the root. Initially, a defense related plant peroxidase cDNA SPI2 (spruce pathogen induced 2) from Norway spruce roots was isolated and sequenced and found to encode a predicted 34kD SPI2 protein. The 34kD SPI2 protein was detected both in the root and shoot of Norway spruce seedlings, and accumulated as a local response to infection with the pathogenic oomycete Pythium dimorphum. In addition, two 38kD and 39kD SPI2 related proteins were detected in roots only after infection. Interestingly, increase levels of the 39kD SPI2 related protein was also detected in shoots of infected seedlings as a systemic response to infection. The putative plant defensin SPI1 (spruce pathogen induced 1) from Norway spruce has been proposed a role in the defense against pathogenic fungi and oomycetes. Here the predicted 5kD SPI1 protein was detected in Norway spruce seedlings and found to accumulate in roots during development. Notably, the putative plant defensin SPI1 lined the wall of cortical root cells, and in roots invaded by P. dimorphum the SPI1 protein was found associated with the invading hyphae. This supports the hypothesis that SPI1 has a role in the defense against pathogenic oomycetes and fungi. The possible protective role of prior colonization by the ectomycorrhizal fungus on later challenge with the pathogen C. polonica, previously known to be vectored to the tree stem by bark beetles, was also examined. Surprisingly, C. polonica was able to invade also roots of both mycorrhizal and non-mycorrhizal seedlings. Not only induced or enhanced plant responses were observed, but also reduced levels of defense-related proteins were observed in the infected roots at the later stages of infection. Decreased levels of SPI1was detected within 96 hours after infection in response to the pathogens tested. Reduced levels of the corresponding transcript was also detected indicating a suppression of host responses by the pathogens. Increased proteolytic activity was detected in infected roots, and from the pathogens. Proteolytic degradation of host proteins by fungal secreted proteases may reduce the levels of potentially antimicrobial proteins enabling the pathogens to effectively invade the roots. Reduced levels of the SPI1 in roots, was found also in response to the ectomycorrhizal fungus L. bicolor. Reduced levels of the peroxidase isozymes at the later stages of the infections, was also observed. Thus, suppressor(s) may be produced by both the pathogens and by the ectomycorrhizal fungus during infection, reducing the host responses and contributing to successful colonization of the roots.
Authors
O. Janne Kjønaas Anne Camilla Bergkvist Arne Olav StuanesAbstract
No abstract has been registered
Authors
Per Holm Nygaard Torbjørn ØdegaardAbstract
Vegetation data were collected in 1931, 1961 and 1991 from permanent plots in a boreo-nemoral forest 20 km north of Oslo in southern Norway. Major changes were found in the vegetation composition during 60 years. The main changes were a reduction in the frequency and frequency of joint occurrence of species like Calluna vulgaris, Vaccinium uliginosum, Trientalis europaea, Maianthemum bifolium, Melampyrum pratense, Cornus suecica, Andromeda polifolia, Eriophorum vaginatum, Vaccinium oxycoccus, Pleurozium schreberi, Hylocomium splendens, Ptilium crista-castrensis, Dicranum fuscescens and Ptilidium ciliare. The observed changes were interpreted as induced by internal processes e.g., a long-term change from paludified forest to mesic forest. In particular the growth of Picea abies seems in particular to be a main driving force. The dominance of Picea abies and Vaccinium myrtillus appears to have made the conditions more unfavourable to other species. A doubling of the living stem biomass of P.abies during the last 67 years shows that this old-growth forest has not reached a steady state. Species like Deschampsia flexuosa and Molinia caerulea did not increase in frequency as has been demonstrated in response to nitrogen deposition elsewhere in northern Europe. The results of this study indicate that protection from logging has promoted the reduction of species in the field layer and bottom layer. This study questions if monitoring of forest vegetation should be restricted to protected forests as is the practice in Scandinavia today. We recommend that areas with some kind of selective cutting are also used for monitoring of forest vegetation
Abstract
No abstract has been registered
Authors
Jan Mulder E. Matzner J.F. Gallardo Edward TippingAbstract
No abstract has been registered
Authors
Jørund RolstadAbstract
No abstract has been registered
Authors
Knute J. Nadelhoffer Bridget A. Emmett Per Gundersen O. Janne Kjønaas Chris J. Koopmans Patrick Schleppi Albert Tietema Richard Frederic WrightAbstract
Humans have altered global nitrogen cycling such that more atmospheric N2 is being converted (\"fixed\") into biologically reactive forms by anthropogenic activities than by all natural processes combined. In particular, nitrogen oxides emitted during fuel combustion and ammonia volatilized as a result of intensive agriculture have increased atmospheric nitrogen inputs (mostly NO3 and NH4) to temperate forests in the Northern Hemisphere.Because tree growth in northern temperate regions is typically nitrogen-limited, increased nitrogen deposition could have the effect of attenuating rising atmospheric CO2 by stimulating the accumulation of forest biomass. Forest inventories indicate that the carbon contents of northern forests have increased concurrently with nitrogen deposition since the 1950s. In addition, variations in atmospheric CO2 indicate a globally significant carbon sink in northern mid-latitude forest regions. It is unclear, however, whether elevated nitrogen deposition or other factors are the primary cause of carbon sequestration in northern forests. Here we use evidence from 15N-tracer studies in nine forests to show that elevated nitrogen deposition is unlikely to be a major contributor to the putative CO2 sink in forested northern temperature regions.
Authors
D. LindgrenAbstract
No abstract has been registered
Authors
O. Janne KjønaasAbstract
Mixtures of cation and anion exchange resins are used as part of the resin core technique to determine nitrogen transformation in forest soils as they adsorb the NH4-N and NO3-N from soil solution percolating through the incubated soil cores. In the field, the exchange resins may be subjected to a variety of conditions, involving drying, rehydration, freezing, and thawing. This paper examines how these processes affect adsorption of NH4-N and NO3-N and the stability of the resins. Lab tests were performed on the anion resin Amberlite IRA-93, the cationresin Amberlite IR-120, and a mixture of IRA-93 and IR-120, and the commercially-mixed bed resin Amberlite MB1. The background content of NO3-N and NH4-N on the resins was large and highly variable between different batches of resins in spite of a 2 M NaCl pre-rinse. The IR-120 cation resin that was subjected to 48 hours air-drying contained significantly less NH4-N than the most resins, while the drying of the IRA-93 anion resin caused a significant release of NO3-N from resins with no N addition. Although the variation was large, the mixed bed resin MB1 indicated a release of NH4-N, which supports results from long term in situ deployments. A reduced adsorption of NO3-N was found on the IRA-93 anion resins and the MB1 mixed bed resins that were dried prior to N addition while the dry IR-120 cation resins adsorbed significantly less NH4-N than the control resin. No effect of freezing the thawing efficiency was observed on resin stability or N adsorption efficiency. Sufficient blanks that have been subjected to similar moisture changes are necessary in N limited systems with low levels of avialable NH4-N and NO3-N.