Publikasjoner
NIBIOs ansatte publiserer flere hundre vitenskapelige artikler og forskningsrapporter hvert år. Her finner du referanser og lenker til publikasjoner og andre forsknings- og formidlingsaktiviteter. Samlingen oppdateres løpende med både nytt og historisk materiale. For mer informasjon om NIBIOs publikasjoner, besøk NIBIOs bibliotek.
2013
Sammendrag
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Sammendrag
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Forfattere
Isabella Børja Jan Světlík Valeriy Nadezhdin Jan Čermák Sabine Rosner Nadezhda NadezhdinaSammendrag
Top-dieback of Norway spruce (Picea abies) trees has been observed in SE Norway. Trees usually die within 1-4 years after the first symptoms become visible and the dieback cause is unknown. The aim of our study was to establish when the irreversible spiral to tree death occurs. We assumed that hydraulic dysfunction, exemplified here by the sap flow reduction, was the final trigger of tree decline. We used the non-destructive heat field deformation method (HFD) to monitor the sap flow density (SFD) in non-symptomatic trees. After felling the trees we used the modified differential translucence method (MDT) to evaluate the sapwood translucence as an additional indicator of its functionality. In this study we show three examples of non-symptomatic trees with widely different sap flow densities detected by the HFD; tree A with unchanged sap flow throughout the monitoring period, tree B with decreasing sap flow in the last formed annual rings and minimal sap flow detected in tree C, which also started to show the first visible signs of dieback. In contrast, the MDT method detected in all cases functional (translucent) sapwood. In conclusion, we show that the sap flow reduction may occur during a relatively short period, prior to occurrence of any visual symptoms. Also, dysfunctions in sap flow could not be detected by the MDT method, as the sapwood still looked translucent and thus functional, although minimal sap flow was detected in that area by HFD method. Here we demonstrate the sensitivity of the HFD method in detecting the quantity of sap flow and thus a suitable diagnostic tool to evaluate the vitality in Norway spruce trees before the onset of visible disease symptoms.
Forfattere
Isabella BørjaSammendrag
Det er ikke registrert sammendrag
Sammendrag
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Forfattere
Isabella BørjaSammendrag
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Forfattere
Nina TrandemSammendrag
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Sammendrag
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Sammendrag
BACKGROUND: To grow remontant strawberries at high latitudes in autumn is challenging because of short days and low light levels. Nevertheless, current day and night temperatures in Norwegian coastal areas up to 63 degrees N are normally sufficient for growth and fruit development till early October, and even higher temperatures can be expected in the future according to climatic scenarios, with potential to prolong the growing season. However, light would be a minimum factor. It is therefore of interest to examine the effects of providing supplemental light when photosynthetic active radiation (PAR) falls below critical level for development of high fruit quality. OBJECTIVE: To examine effects on fruit yield parameters, fruit tension, Brix° and arthropod numbers, in order to investigate the potential of LED lighting using diodes giving red and blue light, as a means to prolong the growing season at northern latitudes. METHOD: In this two-year study remontant strawberry cvs ‘Everest’ and ‘Rondo’ were grown in high polytunnels. Two LED lighting levels (LED100 and LED300) were applied from 7 Pm to 7 AM, whenever light intensity fell below 400 μmol m−2 s−1 from first week of September, and compared to ambient light (control). The LED300 was peaking at wavelengths of 460 nm and 660 nm, respectively blue and red, and the relation between blue and red light was 1 : 8; LED100 delivered similar wavelengths but the blue to red relation was 2 : 8. Fruit yield, soluble solids (Brix°), fruit firmness, temperature (°C), dew point (°C), and PAR light (μmol m−2 s−1) were recorded. The experimental design was block with four replications. The lamps were hung with the light source 40 cm above top of canopy, giving a PAR radiation at top of canopy of LED100 and LED300 of respectively 900 and 258 μmol m−2 s−1. RESULTS: LED improved fruit yield and quality, but more at 900 than at 258 μmol m−2 s−1. However, highest light level was probably beyond the saturation point for photosynthesis, at least in early morning and late evening and the last three weeks of the harvesting season, because of low temperatures. Some fruit yield was not harvested because of too low temperatures to achieve ripen fruits after mid-October. Arthropods were sampled from ‘Rondo’ leaves 2–3 times per season, and aphids, spider mites and predatory mites (introduced) were the most numerous groups. LED significantly decreased the number of spider mites in the autumn. CONCLUSIONS: LED lighting has potential as light source growing remontant strawberries in high polytunnels, when PAR radiation is below 400 μmol m−2 s−1. However, to benefit fully of the light it would be necessary to grow the plants in winter tunnels and add heating. That would increase the yields significantly compared with our results.
Forfattere
Nina TrandemSammendrag
Det er ikke registrert sammendrag