bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoperiod and Androgens Act Independently to Induce Spinal Nucleus of the Bulbocavernosus Neuromuscular Plasticity in the Siberian Hamster, Phodopus sungorus
Authors: Hegstrom C. D. , Jordan C. L. , Breedlove S. M. 
Published: March 2003

AbstractIn the Siberian hamster, Phodopus sungorus, short‐day photoperiods induce the winter phenotype, which in males includes a decrease in the production of androgens and changes in physiology to inhibit reproduction. Motoneurones of the spinal nucleus of the bulbocavernosus (SNB) and their target muscles, the bulbocavernosus and the levator ani, a neuromuscular system involved in male copulation, also display seasonal plasticity in P. sungorus. It is not known whether the plasticity seen in the SNB system of gonadally intact hamsters is due to the effects of photoperiod per se, or to the photoperiod‐induced changes in androgen production. To answer this question, we castrated adult male hamsters from long days and then implanted them with capsules containing either testosterone or blanks. Half of the hamsters from each hormone condition were moved into short photoperiod (8 : 16 h light/dark cycle) while the rest were maintained under long‐day conditions (15 : 9 h light/dark cycle). After 15 weeks, many measures of the SNB system, such as somata size and weight of target muscles, responded only to androgen, not to photoperiod. However, there were effects of photoperiod on the neuromuscular junctions (NMJs) that were independent of androgen status. For example, the number of synaptic zones per NMJ and the area of the NMJs were significantly increased by short days and/or testosterone treatment. The two factors exerted an additive, rather than an interactive, effect on these measures. Another striated muscle, the extensor digitorum longus, which is present in both sexes and plays no specialized role in reproduction, displayed neither an effect of androgen nor of photoperiod on fibre size or NMJ structure. These results suggest that, in addition to androgenic effects on SNB plasticity, there is also an androgen‐independent effect of photoperiod on the SNB neuromuscular system.
Effects of elevated ozone and low light on diurnal and seasonal carbon gain in sugar maple
Authors: Topa M. A. , Vanderklein D. W. , Corbin A. 
Published: March 2003

AbstractThe long‐term interactive effects of ozone and light on whole‐tree carbon balance of sugar maple (Acer saccharumMarsh.) seedlings were examined, with an emphasis on carbon acquisition, foliar partitioning into starch and soluble sugars, and allocation to growth. Sugar maple seedlings were fumigated with ambient, 1·7 × ambient and 3·0 × ambient ozone in open‐top chambers for 3 years under low and high light (15 and 35% full sunlight, respectively). Three years of ozone fumigation reduced the total biomass of seedlings in the low‐ and high‐light treatments by 64 and 41%, respectively, but had no effect on whole‐plant biomass allocation. Ozone had no effect on net photosynthesis until late in the growing season, with low‐light seedlings generally exhibiting more pronounced reductions in photosynthesis. The late‐season reduction in photosynthesis was not due to impaired stomatal function, but was associated more with accelerated senescence or senescence‐like injury. In contrast, the 3·0 × ambient ozone treatment immediately reduced diurnal starch accumulation in leaves by over 50% and increased partitioning of total non‐structural carbohydrates into soluble sugars, suggesting that injury repair processes may be maintaining photosynthesis in late spring and early summer at the expense of storage carbon. The results in the present study indicate that changes in leaf‐level photosynthesis may not accurately predict the growth response of sugar maple to ozone in different light environments. The larger reduction in seedling growth under low‐light conditions suggests that seedlings in gap or closed‐canopy environments are more susceptible to ozone than those in a clearing. Similarly, understanding the effects of tropospheric ozone on net carbon gain of a mature tree will require scaling of leaf‐level responses to heterogeneous light environments, where some leaves may be more susceptible than others.
Direct and indirect effects of elevated CO2 on leaf respiration in a forest ecosystem
Authors: Hamilton J. G. , Thomas R. B. , Delucia E. H. 
Published: March 2003

AbstractWe measured the short‐term direct and long‐term indirect effects of elevated CO2 on leaf dark respiration of loblolly pine (Pinus taeda) and sweetgum (Liquidambar styraciflua) in an intact forest ecosystem. Trees were exposed to ambient or ambient + 200 µmol mol−1 atmospheric CO2 using free‐air carbon dioxide enrichment (FACE) technology. After correcting for measurement artefacts, a short‐term 200 µmol mol−1 increase in CO2 reduced leaf respiration by 7–14% for sweetgum and had essentially no effect on loblolly pine. This direct suppression of respiration was independent of the CO2 concentration under which the trees were grown. Growth under elevated CO2 did not appear to have any long‐term indirect effects on leaf maintenance respiration rates or the response of respiration to changes in temperature (Q10, R0). Also, we found no relationship between mass‐based respiration rates and leaf total nitrogen concentrations. Leaf construction costs were unaffected by growth CO2 concentration, although leaf construction respiration decreased at elevated CO2 in both species for leaves at the top of the canopy. We conclude that elevated CO2 has little effect on leaf tissue respiration, and that the influence of elevated CO2 on plant respiratory carbon flux is primarily through increased biomass.
Polyamine metabolism in barley reacting hypersensitively to the powdery mildew fungus Blumeria graminis f. sp. hordei
Authors: Cowley T. , Walters D. R. 
Published: March 2003

AbstractPolyamine levels and activities of enzymes of polyamine biosynthesis and catabolism were examined in the barley cultivar Delibes (Ml1al + Ml(Ab)) reacting hypersensitively to the powdery mildew fungus, Blumeria graminis f. sp. hordei (race CC220). Levels of free putrescine and spermine and of conjugated forms of putrescine, spermidine and spermine were greatly increased 1–4 d following inoculation of barley with the powdery mildew. These changes in polyamine levels were accompanied by elevated activities of the polyamine biosynthetic enzymes ornithine decarboxylase (ODC), arginine decarboxylase (ADC) and S‐adenosylmethionine decarboxylase (AdoMetDC) and the polyamine catabolic enzymes diamine oxidase (DAO) and polyamine oxidase (PAO). Activities of two enzymes involved in conjugating polyamines to hydroxycinnamic acids, putrescine hydroxycinnamoyl transferase (PHT) and tyramine feruloyl‐CoA transferase (TFT) were also examined and were found to increase significantly 1–4 d after inoculation. The possibility that the increased levels of free spermine, increased polyamine conjugates, and increased DAO and PAO activities are involved in development of the hypersensitive response of Delibes to powdery mildew infection is discussed.
Stomatal and photosynthetic responses of olive (Olea europaea L.) leaves to water deficits
Authors: Moriana A. , Villalobos F. J. , Fereres E. 
Published: March 2003

AbstractThe leaf gas exchange of mature olive trees (Olea europaea L.) was characterized over a wide range of water deficits in the field during 1998, in Cordoba, Spain. Leaf photosynthesis (A) and stomatal conductance (gl) responded diurnally and seasonally to variations in tree water status and evaporative demand. In the absence of water stress, A and gl were generally high during autumn and low in days of high vapour pressure deficits (VPD). Leaf A varied between 0 and 2 µmol m−2 s−1 under severe water deficits that lowered the stem water potential (Ψx) to −8·0 MPa, but recovered rapidly following rehydration. Transpiration efficiency (TE) was curvilinearly related to VPD and not influenced by water deficits except in cases of severe water stress, where low TE values were observed at Ψx below −4 MPa. Three models of leaf conductance were calibrated and validated with the experimental data; two were based on the model proposed by Leuning (L) and the other was derived from the widely used Jarvis (J) model. The L models performed better than the J model in two validation tests. The scatter of the predictions and the limited accuracy of all three models suggest that, in addition to the physiological and environmental variables considered, there are additional endogenous factors influencing the gl of olive leaves.
Three‐dimensional reconstructions of the Achilles tendon insertion in man
Authors: Milz S. , Rufai A. , Buettner A. , Putz R. , Ralphs J. R. , Benjamin M. 
Published: March 2003

AbstractThe distribution of type II collagen in sagittal sections of the Achilles tendon has been used to reconstruct the three‐dimensional (3D) shape and position of three fibrocartilages (sesamoid, periosteal and enthesis) associated with its insertion. The results showed that there is a close correspondence between the shape and position of the sesamoid and periosteal fibrocartilages – probably because of their functional interdependence. The former protects the tendon from compression during dorsiflexion of the foot, and the latter protects the superior tuberosity of the calcaneus. When the zone of calcified enthesis fibrocartilage and the subchondral bone are mapped in 3D, the reconstructions show that there is a complex pattern of interlocking between pieces of calcified fibrocartilage and bone at the insertion site. We suggest that this is of fundamental importance in anchoring the tendon to the bone, because the manner in which a tendon insertion develops makes it unlikely that many collagen fibres pass across the tissue boundary from tendon to bone. When force is transmitted to the bone from a loaded tendon, it is directed towards the plantar fascia by a series of highly orientated trabeculae that are clearly visible in 3D in thick resin sections.
Simulating spatially and physiologically structured populations
Authors: Gurney William S. C. , Speirs Douglas C. , Wood Simon N. , Clarke Elizabeth D. , Heath Michael R. 
Published: March 2003

Summary

Population dynamics are frequently the product of a subtle interplay between development and dispersal in an inhomogeneous environment. Simulations of spatially inhomogeneous populations with physiologically distinguishable individuals are a known source of numerical difficulty.
This paper reports a new and highly efficient algorithm for this problem, whose accuracy we demonstrate by comparison with conventional numerical solutions of one‐dimensional problems.
As an illustration, we construct a two (space)‐dimensional model of a copepod (Calanus finmarchicus) in the NE Atlantic, and demonstrate that its predictions correspond closely with those of an equivalent Lagrangian ensemble.
Estimating the force of infection;Mycobacterium bovisinfection in feral ferretsMustela furoin New Zealand
Authors: Caley Peter , Hone Jim 
Published: March 2003

SummaryThe force ofMycobacterium bovisinfection (λ) in feral ferretMustela furopopulations in New Zealand was estimated, by fitting candidate models to age‐specific disease‐prevalence data. The candidate models were constructed from a set of a priori hypotheses of howM. bovisinfection is transmitted to ferrets, and model selection used to assess the degree of support for each hypothesis.The estimated force ofM. bovisinfection ranged between five sites from 0·14 year−1to 5·8 year−1, and was twofold higher in males than in females.The data most strongly supported the hypothesis that transmission ofM. bovisto ferrets occurs from the ingestion ofM. bovis‐infected material from the age of weaning, as modelled by the force of infection being zero up to the age of weaning, and constant thereafter. Other candidate transmission hypotheses (e.g. mating, suckling, routine social interaction) and combinations thereof were unsupported in comparison, and hence it was concluded that transmission from these postulated mechanisms must be insignificant compared with dietary‐related transmission.The preferred transmission hypothesis was nearly equally supported regardless of whether disease‐induced mortality was included or not, although omitting disease‐induced mortality resulted in a lower force of infection estimate. The dietary transmission hypothesis (omitting disease‐induced mortality) could be easily represented by a generalized linear model, enabling simple analysis of critical experiments designed to identify the source ofM. bovisinfection in feral ferrets.
The effect of plant species on soil nitrogen mineralization
Authors: Van Der Krift Tanja A. J. , Berendse Frank 
Published: March 2003

Summary To ascertain the influence of different plant species on nitrogen (N) cycling, we performed a long‐term garden experiment with six grasses and five dicots with different potential growth rates, that are adapted to habitats with different nutrient supplies. We measuredin situN mineralization and nitrification of the soil under monocultures of each species during the fourth year of the experiment. We focused on the effects of the different species on (i) annual net N mineralization; (ii) the seasonal pattern of N mineralization; and (iii) the fraction of the total N mineralization that is nitrified. Our hypothesis was that plant species of nutrient‐rich habitats would enhance the N mineralization compared with species of nutrient‐poor habitats. The results demonstrate a strong influence of the species on net N mineralization and net nitrification, both of which fluctuated strongly during the year. Overall, species from high fertility habitats increased N mineralization and nitrification more than species from low fertility habitats. About 90% of the mineralized ammonium was oxidized to nitrate. There was no significant difference in this proportion in the plots of species from nutrient‐rich, moderate and nutrient‐poor habitats.
Nitrogen deposition and forest expansion in the northern Great Plains
Authors: Köchy Martin , Wilson Scott D. 
Published: March 2003

SummaryAtmospheric nitrogen (N) deposition has become one of the most important agents of vegetation change in densely populated regions. It may also contribute to forest expansion into grasslands at the northern edge of the North American Great Plains.We measured N deposition and available soil N with ion‐exchange resin over 2 years in six national parks in areas varying in population density and industrialization. N deposition was significantly higher in four parks in densely populated regions than in two remote parks.Available soil N increased significantly with N deposition across all parks.We measured N mass and15N abundance (δ15N) in vegetation and soil in two parks: Elk Island, receiving 22 kg N ha−1 year−1, and Jasper, receiving 8 kg N ha−1 year−1. Differences between parks in tissue N concentrations were small, but forest expansion over five decades resulted in the mass of N in vegetation increasing by 74% in Elk Island but by only 26% in Jasper. δ15N in forest vegetation was significantly lower in Elk Island than in Jasper, suggesting that anthropogenic sources contribute significantly to the high rates of N entering that ecosystem.We determined the rate of forest expansion within parks using six decades of aerial photographs. Parks in aspen parkland and boreal forest showed a strong positive relationship between forest expansion and N deposition. The relationships found between N deposition, available soil N and forest expansion suggest that even comparatively low rates of N deposition may accelerate the expansion of forest into temperate grasslands.
Plant biomass and production and CO2 exchange in an ombrotrophic bog
Authors: Moore Tim R. , Bubier Jill L. , Frolking Steve E. , Lafleur Peter M. , Roulet Nigel T. 
Published: March 2003

Summary

Above‐ground biomass was measured at bog hummock, bog hollow and poor‐fen sites in Mer Bleue, a large, raised ombrotrophic bog near Ottawa, Ont., Canada. The average above‐ground biomass was 587 g m−2 in the bog, composed mainly of shrubs and Sphagnum capitula. In the poor fen, the average biomass was 317 g m−2, comprising mainly sedges and herbs and Sphagnum capitula. Vascular plant above‐ground biomass was greater where the water table was lower, with a similar but weaker relationship for Sphagnum capitula and vascular leaf biomass.
Below‐ground biomass averaged 2400 g m−2 at the bog hummock site, of which 300 g m−2 was fine roots (< 2 mm diameter), compared with 1400 g m−2 in hollows (fine roots 450 g m−2) and 1200 g m−2 at the poor‐fen site.
Net Ecosystem Exchange (NEE) of CO2 was measured in chambers and used to derive ecosystem respiration and photosynthesis. Under high light flux (PAR of 1500 µmol m−2 s−1), NEE ranged across sites from 0.08 to 0.22 mg m−2 s−1 (a positive value indicates ecosystem uptake) in the spring and summer, but fell to –0.01 to –0.13 mg m−2 s−1 (i.e. a release of CO2) during a late‐summer dry period.
There was a general agreement between a combination of literature estimates of photosynthetic capacity for shrubs and mosses and measured biomass and summer‐time CO2 uptake determined by the eddy covariance technique within a bog footprint (0.40 and 0.35–0.40 mg m−2 s−1, respectively).
Gross photosynthesis was estimated to be about 530 g m−2 year−1, total respiration 460 g m−2 year−1, and export of DOC, DIC and CH4 10 g m−2 year−1, leaving an annual C sequestration rate of 60 g m−2 year−1. Root production and decomposition are important parts of the C budget of the bog. Root C production was estimated to be 161–176 g m−2 year−1, resulting in fractional turnover rates of 0.2 and 1 year−1 for total and fine roots, respectively.
Episodic regeneration at the Nothofagus pumilio alpine timberline in Tierra del Fuego, Chile
Authors: Cuevas Jaime G. 
Published: March 2003

Summary

The short‐ and long‐term dynamics of Nothofagus pumilio were investigated across an altitudinal gradient in Tierra del Fuego. Declining probability of establishment of individuals with increasing altitude (spatial restriction) is expected to lead to increasingly sporadic recruitment towards the alpine timberline (AT) (temporal restriction). Longevity of adult trees and difficulties in establishment at altitude should result in a static AT.
The number of annual growth buds of seedlings suggests that the species regenerates episodically at all altitudes in cycles of a similar length (7–8 years) to those for seed production. Nevertheless, the seedling density in a year of high regeneration (1996) was considerably higher at lower altitudes than at the AT.
Counting of the growth rings of adult individuals revealed a massive episode of establishment between 1800 and 1850 at all altitudes. There was poor establishment between 1920 and 1980. The age range for the entire population fluctuated between 49 and 377 years in 1996.
Although there is no evidence for more frequent recruitment at lower altitudes, differential regeneration ensures that establishment there is more probable.
Individuals at the AT had an average age of 160 years in 1996, suggesting that the border has indeed remained static for at least a century and a half.
The spatial restriction determines that the AT cannot advance until removal of the temporal restriction allows turnover to occur.
VANQUIS, a system for the interactive semantic content analysis and spatio‐temporal query by content of videos
Authors: Machtynger J. , Shotton D. M. 
Published: March 2003

SummaryUsing the video metadata descriptors and data model defined in the accompanying paper (Shotton, D. M.et al.(2002) A metadata classification schema for semantic content analysis of videos.J. Microsc.205, 33–42), we discuss how analysis of the content of scientific videos, and subsequent query by content of the resulting semantic metadata, can be enhanced by the use of an object‐relational database. We illustrate this by describingVANQUIS, a Web‐based prototypevideoanalysis andqueryinterfacesystemfor the interactive spatio‐temporal analysis and subsequent query by content of videos. UsingVANQUISto generate standard SQL (structured query language) statements that address complex data types stored in an object‐relational database, relationships between characters and events contained within and between videos can be identified, and the appropriate video segments containing these characters and events can be retrieved for viewing. We give examples of analysis and query implementation by usingVANQUISto analyse a biological microscopy video, and discuss the wider potential of this methodology for the analysis and query by content of videos containing more general subject matter.
On the role of electron–ion recombination in low vacuum scanning electron microscopy
Authors: Toth M. , Thiel B. L. , Donald A. M. 
Published: March 2003

SummaryHere we demonstrate the effects of electron–ion recombination on imaging signals utilized in low vacuum scanning electron microscopes (SEMs). The presented results show that, under normal operating conditions, recombination of ionized gas molecules with secondary electrons (SEs) suppresses a significant fraction of emitted electrons. If the ion flux (and hence the spatial dependence of the SE–ion recombination rate) is laterally inhomogeneous across the imaged region of a specimen, contrast in SE images can be influenced and in some cases (under conditions of high detector field strength and long ionic mean free path) dominated by variations in the recombination rate. Consequently, SE images of features such as topographic asperities can exhibit edge‐darkening, leading to inversion of some topographic contrast. Recognition of the extent and nature of electron–ion recombination is required for a correct understanding of processes occurring in variable pressure SEMs and, subsequently, for models of image formation.
A technique for the examination of polar ice using the scanning electron microscope
Authors: Barnes P. R. F. , Mulvaney R. , Wolff E. W. , Robinson K. 
Published: March 2003

SummaryThe microstructure and location of impurities in polar ice are of great relevance to ice core studies. We describe a reliable method to examine ice in the scanning electron microscope (SEM). Specimens were cut in a cold room and could have their surfaces altered by sublimation either before (pre‐etching) or after (etching) introduction to the cryo‐chamber of the SEM. Pre‐etching was used to smooth surfaces, whilst etching stripped away layers from the specimen surface, aiding the location of particles in situ, and allowing embedded structures to be revealed. X‐ray analysis was used to determine the composition of localized impurities, which in some cases had been concentrated on the surface by etching. Examining uncoated surfaces was found to be advantageous and did not detract from qualitative X‐ray analysis. Imaging uncoated was performed at low accelerating voltages and probe currents to avoid problems of surface charging.