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41.
Arne Stensvand Håvard Eikemo Robert C. Seem David M. Gadoury 《European journal of plant pathology / European Foundation for Plant Pathology》2009,125(1):173-178
Darkness suppresses ascospore release in Venturia inaequalis, but the impact of light levels during the extended twilight and dusk that typify Nordic spring conditions is poorly understood.
Volumetric spore traps were operated at two different locations in Norway over several years. During the season of asocspore
release (approximately 1 April to 30 June), on 25 occasions when rain started during night (after 23:00 h and before 04:00 h)
and leaves remained wet until at least midnight the following day, the cumulative percentage of spores trapped at sunrise
did not exceed 1%, irrespective of temperature. Three hours after sunrise, cumulative ascospore release reached 0.8%, 3.0%,
and 8.1% at temperatures of 0 to 5°C, 5 to 10°C, and >10°C, respectively, and 50% release occurred at 11, 9, and 8 h after
sunrise. Additional field and laboratory studies indicated that the protracted dawn and dusk of Nordic latitudes, either alone
or in combination with low temperatures, does not substantially alter previously reported patterns of ascospore release. 相似文献
42.
The Alstroemeria cultivars Diamond, King Cardinal and Libelle were grown for 18 months under five lighting regimes with, and without, soil cooling. The aim was to optimize the daily investment of light energy from artificial sources with respect to photoperiod and photosynthetic fluence rates and to elucidate possible links between reactions to photoperiod and root-zone temperature. The more photons (photosynthetically active radiation, PAR) that were supplied to the plants per day (8, 11 and 13 mol m−2), the higher was the total production of flowering stems. The total yield from regimes with 13 mol m−2 day−1 was higher when the light was spread over 20 and 16 h compared to 12 h. In treatments with soil cooling, the plants flowered continuously under all combinations of photoperiods and photosynthetic fluence rates, and the summer and autumn recession in flower production that occurred for non-cooled ‘King Cardinal' and ‘Diamond' was the same under all lighting regimes. It is concluded that it might be more cost-effective to spread the daily investment of light over 20 rather than 16 or 12 h when the total energy budget and CO2 costs are taken into consideration. 相似文献
43.
Abstract – We explored the incidence of individual feeding specialisation among a naïve predator (non‐native rainbow trout postsmolts) and two native experienced predators (sea‐run Arctic charr and sea‐trout) in a subarctic Norwegian fjord. Interindividual foraging niche stability was obtained by combining information on stomach contents (recent dietary niche) with trophically transmitted parasite infestation (time‐integrated historical dietary niche) of individual predators. Individual fish showed a high degree of resource specialisation as prey items such as gammarids and small fish (both potential intermediate host of parasites) rarely co‐occurred in stomachs. In both naïve and veteran predators, positive associations between the intensity of a specific parasite species and the occurrence of their respective intermediate host (gammarids or fish) in the stomachs of individual predators demonstrated temporally interindividual feeding specialisations. Several behavioural phenotypes clearly co‐existed in both naïve and veteran predator populations, including gammaridivore (benthic feeders), piscivore (pelagic feeders) or insectivore (pleuston feeders) individuals. The likely mechanism of this observed interindividual resource specialisation in the non‐native naïve predators involves a behavioural component of which rapid learning seems to be a key factor. 相似文献
44.
Modestas Keblys Arne Flåøyen Wenche Langseth 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(3):155-160
Samples of winter wheat (n =84), winter rye (46) and barley (29) were collected from the larger family farms and from partnerships in Lithuania just after the 1998 harvest. The number of samples collected from each region was proportional to the amount of grain produced in it. The levels of the Fusarium toxins deoxynivalenol (DON), 3-acetyl-DON, 15-acetyl-DON, nivalenol (NIV), fusarenon-X (4-acetyl-NIV), T-2 toxin, HT-2 toxin, 4,5-diacetoxyscirpenol (DAS), 1,5-monoacetoxyscirpenol (MAS) and scirpentriol in the grain were determined by gas chromatography with mass-selective detection (GC-MS). DON was most often detected in the wheat and rye samples and NIV in the barley samples. The concentrations found were lower than those causing acute or chronic toxic effects in livestock or humans. No fusarenon-X or 15-acetyl-DON was detected, and only small amounts of other trichothecenes were present. Climatic conditions in Lithuania in the summer of 1998 were slightly cooler and wetter than the average for the 1992-1996 but were close to the norm. Because the samples analysed were representative of grain produced for the market in seasons with normal weather, trichothecene contamination of grain from large family farms and partnerships would not be expected to be a problem in most years. 相似文献
45.
Urban forest management needs information about the amount andkinds of recreation use, in particular about emerging recreationalactivities such as Nordic walking and winter bicycling. Between2003 and 2004, year-round use levels of recreational activitieswere investigated in a forest in Vienna using permanent time-lapsevideo recording and counts by human observers on sampling days.The amount of use, yearly, weekly and daily use patterns, aswell as the group size of the traditional activity groups werecompared with Nordic walking and winter bicycling to characterizethese activities and to better understand recreation use. Forall activity groups, the rates of participation varied significantlyacross most of the time dimensions, and the relationships betweenthe time of day and rates of participation were different forindividuals and groups. Nordic walkers displayed a temporaluse pattern similar to that of jogging with workday eveningand weekend morning use peaks, while winter bicycling was similarto bicycling activities with afternoon use peaks during snowyperiods. Nordic walking and winter bicycling activities addedto the multi-use character of the heavily used forest, but seemednot to increase the potential for user conflicts because ofthe current low participation rates and the Nordic walking group'savoidance of times of heavy use. 相似文献
46.
Responses of leaf conductance (g
L) to variation in environmental and plant hydraulic factors were examined on intact and detached shoots of little-leaf linden
(Tilia cordata Mill.) with respect to branch position in the crown. Using detached shoots, we manipulated leaf water supply and light availability
in order to separate the effects of insufficient hydraulic supply and low irradiance. The intact upper-crown leaves demonstrated
2.0–2.2 times higher (P < 0.001) daily maxima of g
L compared to the lower-crown leaves growing in the shadow of upper branches. Mean soil-to-leaf conductance (G
T) was 1.9 times higher (P < 0.001) for the upper-crown foliage compared to that of the lower crown. The total hydraulic resistance was distributed:
soil to distal shoots—41–51%, 25-cm distal shoots—10–15% and leaves—39–44%. In lower branches, g
L was constrained by both low light availability and limited water supply; in upper branches, only by irradiance. Artificial
reduction of hydraulic constraints raised bulk leaf water potential (Ψ
L) and made g
L less sensitive to changes in both atmospheric and plant factors. Stomatal responses to leaf-to-air vapour pressure difference
(VPD) were significantly modified by leaf water status: high Ψ
L seemingly inverted the g
L versus VPD relationship. Enhanced water supply increased g
L and transpiration rate (E) in the lower-crown foliage, but not in the upper-crown foliage. The results support the idea that leaves in the lower canopy
are hydraulically more constrained than those in the upper canopy. 相似文献
47.
48.
ABSTRACT We evaluated direct and interactive effects of light quality and intensity, temperature and light, diurnal rhythms, and timing of high relative humidity during long day lengths on sporulation of Bremia lactucae, the causal agent of lettuce downy mildew, using inoculated lettuce seedlings and detached cotyledons. Suppression of sporulation by light was strongly dependent upon temperature and there was little suppression at =10 degrees C. The most suppressive waveband was in the range from 400 to 450 nm, although a lesser effect of wavebands from 450 to 500 and 500 to 550 nm could be detected. At 15 degrees C, near the lower threshold for suppression of sporulation by light, a clear diurnal pattern of sporulation was observed independent of light and darkness. This diurnal rhythm potentially could interact with light and temperature to confound the results of controlled environment studies, and may be the controlling factor in timing of sporulation at low temperatures. Forecasting models that currently use sunrise and sunset to delimit periods conducive to sporulation can be adapted to short nights and extended twilight conditions by incorporating the effects reported herein. Additionally, models of sporulation could be adapted to better reflect a decrease or absence of the suppressive effect of light at <15 degrees C. 相似文献
49.
Herbert A Gerry NP McQueen MB Heid IM Pfeufer A Illig T Wichmann HE Meitinger T Hunter D Hu FB Colditz G Hinney A Hebebrand J Koberwitz K Zhu X Cooper R Ardlie K Lyon H Hirschhorn JN Laird NM Lenburg ME Lange C Christman MF 《Science (New York, N.Y.)》2006,312(5771):279-283
Obesity is a heritable trait and a risk factor for many common diseases such as type 2 diabetes, heart disease, and hypertension. We used a dense whole-genome scan of DNA samples from the Framingham Heart Study participants to identify a common genetic variant near the INSIG2 gene associated with obesity. We have replicated the finding in four separate samples composed of individuals of Western European ancestry, African Americans, and children. The obesity-predisposing genotype is present in 10% of individuals. Our study suggests that common genetic polymorphisms are important determinants of obesity. 相似文献
50.