bluuebunny/crossref_metadata_2025 huggingface dataset:
The Cytokinin Requirement for Cell Division in Cultured Nicotiana plumbaginifolia Cells Can Be Satisfied by Yeast Cdc25 Protein Tyrosine Phosphatase. Implications for Mechanisms of Cytokinin Response and Plant Development
Authors: Zhang Kerong , Diederich Ludger , John Peter C.L.
Published: December 2004

Cultured cells of Nicotiana plumbaginifolia, when deprived of exogenous cytokinin, arrest in G2 phase prior to mitosis and then contain cyclin-dependent protein kinase (CDK) that is inactive because phosphorylated on tyrosine (Tyr). The action of cytokinin in stimulating the activation of CDK by removal of inhibitory phosphorylation from Tyr is not a secondary downstream consequence of other hormone actions but is the key primary effect of the hormone in its stimulation of cell proliferation, since cytokinin could be replaced by expression of cdc25, which encodes the main Cdc2 (CDK)-Tyr dephosphorylating enzyme of yeast (Saccharomyces cerevisiae). The cdc25 gene, under control of a steroid-inducible promoter, induced a rise in cdc25 mRNA, accumulation of p67Cdc25 protein, and increase in Cdc25 phosphatase activity that was measured in vitro with Tyr-phosphorylated Cdc2 as substrate. Cdc25 phosphatase activity peaked during mitotic prophase at the time CDK activation was most rapid. Mitosis that was induced by cytokinin also involved increase in endogenous plant CDK Tyr phosphatase activity during prophase, therefore indicating that this is a normal part of plant mitosis. These results suggest a biochemical mechanism for several previously described transgene phenotypes in whole plants and suggest that a primary signal from cytokinin leading to progression through mitosis is the activation of CDK by dephosphorylation of Tyr.
Identification in Pea Seed Mitochondria of a Late-Embryogenesis Abundant Protein Able to Protect Enzymes from Drying
Authors: Grelet Johann , Benamar Abdelilah , Teyssier Emeline , Avelange-Macherel Marie-Hélène , Grunwald Didier , Macherel David
Published: December 2004

Late-embryogenesis abundant (LEA) proteins are hydrophilic proteins that accumulate to a high level in desiccation-tolerant tissues and are thus prominent in seeds. They are expected to play a protective role during dehydration; however, functional evidence is scarce. We identified a LEA protein of group 3 (PsLEAm) that was localized within the matrix space of pea (Pisum sativum) seed mitochondria. PsLEAm revealed typical LEA features such as high hydrophilicity and repeated motifs, except for the N-terminal transit peptide. Most of the highly charged protein was predicted to fold into amphiphilic α-helixes. PsLEAm was expressed during late seed development and remained in the dry seed and throughout germination. Application of the stress hormone abscisic acid was found to reinduce the expression of PsLEAm transcripts during germination. PsLEAm could not be detected in vegetative tissues; however, its expression could be reinduced in leaves by severe water stress. The recombinant PsLEAm was shown to protect two mitochondrial matrix enzymes, fumarase and rhodanese, during drying in an in vitro assay. The overall results constitute, to our knowledge, the first characterization of a LEA protein in mitochondria and experimental evidence for a beneficial role of a LEA protein with respect to proteins during desiccation.
Site Preferences of Insertional Mutagenesis Agents in Arabidopsis
Authors: Pan Xiaokang , Li Yong , Stein Lincoln
Published: December 2004

We have performed a comparative analysis of the insertion sites of engineered Arabidopsis (Arabidopsis thaliana) insertional mutagenesis vectors that are based on the maize (Zea mays) transposable elements and Agrobacterium T-DNA. The transposon-based agents show marked preference for high GC content, whereas the T-DNA-based agents show preference for low GC content regions. The transposon-based agents show a bias toward insertions near the translation start codons of genes, while the T-DNAs show a predilection for the putative transcriptional regulatory regions of genes. The transposon-based agents also have higher insertion site densities in exons than do the T-DNA insertions. These observations show that the transposon-based and T-DNA-based mutagenesis techniques could complement one another well, and neither alone is sufficient to achieve the goal of saturation mutagenesis in Arabidopsis. These results also suggest that transposon-based mutagenesis techniques may prove the most effective for obtaining gene disruptions and for generating gene traps, while T-DNA-based agents may be more effective for activation tagging and enhancer trapping. From the patterns of insertion site distributions, we have identified a set of nucleotide sequence motifs that are overrepresented at the transposon insertion sites. These motifs may play a role in the transposon insertion site preferences. These results could help biologists to study the mechanisms of insertions of the insertional mutagenesis agents and to design better strategies for genome-wide insertional mutagenesis.
Endoplasmic Reticulum-Associated Degradation of Ricin A Chain Has Unique and Plant-Specific Features
Authors: Di Cola Alessandra , Frigerio Lorenzo , Lord J. Michael , Roberts Lynne M. , Ceriotti Aldo
Published: December 2004

Proteins that fail to fold in the endoplasmic reticulum (ER) or cannot find a pattern for assembly are often disposed of by a process named ER-associated degradation (ERAD), which involves transport of the substrate protein across the ER membrane (dislocation) followed by rapid proteasome-mediated proteolysis. Different ERAD substrates have been shown to be ubiquitinated during or soon after dislocation, and an active ubiquitination machinery has been found to be required for the dislocation of certain defective proteins. We have previously shown that, when expressed in tobacco (Nicotiana tabacum) protoplasts, the A chain of the heterodimeric toxin ricin is degraded by a pathway that closely resembles ERAD but is characterized by an unusual uncoupling between the dislocation and the degradation steps. Since lysine (Lys) residues are a major target for ubiquitination, we have investigated the effects of changing the Lys content on the retrotranslocation and degradation of ricin A chain in tobacco protoplasts. Here we show that modulating the number of Lys residues does not affect recognition events within the ER lumen nor the transport of the protein from this compartment to the cytosol. Rather, the introduced modifications have a clear impact on the degradation of the dislocated protein. While the substitution of the two Lys residues present in ricin A chain with arginine slowed down degradation, the introduction of four extra lysyl residues had an opposite effect and converted the ricin A chain to a standard ERAD substrate that is disposed via a process in which dislocation and degradation steps are tightly coupled.
Vygotsky's Zone of Proximal Development and Krashen's i+1: Incommensurable Constructs; Incommensurable Theories
Authors: Dunn William E. , Lantolf James P.
Published: December 2004

Second language scholars, in public research and in public discussions,have suggested that Krashen's construct of i+1is similar to Vygotsky's zone of proximal development and that it might therefore befeasible to integrate the two constructs in a way that would be productive for second languageacquisition (SLA) research. After surveying publications relevant to the issue, we argue that thisenterprise is futile, not only because the concepts are unrelatable, but also because they arerooted in incommensurable theoretical discourses. We also propose a way in which SLAresearch and theory might deal with incommensurability.
An Implementation of the Mode‐Split Traffic‐Assignment Method
Authors: Boilé Maria P. , Spasovic Lazar N.
Published: December 2004

This article presents the exact formulation and solution of an integrated mode‐choice traffic‐assignment model. The model incorporates theoretically sound behavioral principles governing mode and route selection. The article also shows how to implement the model within powerful mathematical programming software and use it to analyze an intermodal transportation network. Results of the analysis show that the model is an excellent educational tool in aiding the understanding of traveler behavioral principles. As a practical tool, the model can be used to provide insights in the analysis of intermodal commuter corridors.
Decentralized Parametric Damage Detection Based on Neural Networks
Authors: Wu Zhishen , Xu Bin , Yokoyama Koichi
Published: December 2004

In this paper, based on the concept of decentralized information structures and artificial neural networks, a decentralized parametric identification method for damage detection of structures with multi‐degrees‐of‐freedom (MDOF) is conducted. First, a decentralized approach is presented for damage detection of substructures of an MDOF structure system by using neural networks. The displacement and velocity measurements from a substructure of a healthy structure system and the restoring force corresponding to this substructure are used to train the decentralized detection neural networks for the purpose of identifying the corresponding substructure. By using the trained decentralized detection neural networks, the difference of the interstory restoring force between the damaged substructures and the undamaged substructures can be calculated. An evaluation index, that is, relative root mean square (RRMS) error, is presented to evaluate the condition of each substructure for the purpose of health monitoring. Although neural networks have been widely used for nonparametric identification, in this paper, the decentralized parametric evaluation neural networks for substructures are trained for parametric identification. Based on the trained decentralized parametric evaluation neural networks and the RRMS error of substructures, the structural parameter of stiffness of each subsystem can be forecast with high accuracy. The effectiveness of the decentralized parametric identification is evaluated through numerical simulations. It is shown that the decentralized parametric evaluation method has the potential of being a practical tool for a damage detection methodology applied to structure‐unknown smart civil structures.
Labour Market Institutions and the Gender Wage Gap in Britain and Australia, 1973–90
Authors: Kidd Michael P. , Shannon Michael
Published: December 2004

The importance of wage structure is frequently interpreted as indirect evidence of the role played by labour market institutions. The current paper follows in this tradition, examining the role of wage structure in explaining the trend in the gender wage gap over the period 1973–91 for both Australia and the UK. The focus is upon whether changes in wage structure (and associated gender wage gap) both across country and over time are compatible with institutional explanations. Combining comparisons both cross‐country and over time yields a more stringent, albeit indirect, test of the role of institutions.
Unemployment Among Britain’s Ethnic Minorities
Authors: Blackaby David , Leslie Derek , Murphy Philip , O’Leary Nigel
Published: December 2004

Using a sample of over 100,000 males from the Labour Force Survey, we explore the employment prospects of different ethnic groups. There are significant differences across groups so that discrimination studies which consider ethnic minorities as one homogeneous group involve a large degree of approximation. We pay particular attention to the considerable differences between the Indian and Pakistani/Bangladeshi groups. We argue that the differences are not the result of different levels of discrimination by the white majority; rather the predominately Muslim Pakistani/Bangladeshi community is less assimilated compared with other ethnic minority groups.
After the Golden Age: A Long‐Run Perspective on Growth Rates That Speeded up, Slowed Down and Still Differ
Authors: Mills Terence C. , Crafts N. F. R.
Published: December 2004

This paper contains an econometric analysis of international convergence in growth allowing for the possibility of several trend breaks. The results offer further evidence against strong hypotheses of convergence but demonstrate the existence of common trends among subsets of countries. Trend growth estimates for OECD countries have fallen since the early post‐war period when catch‐up was strong, but nevertheless are generally higher than before the Second World War. Taking these results together with evidence from historical research, it is argued that the recent growth slowdown should not be seen as sufficient reason to reject the hypothesis of endogenous growth.
On Quantifier Domain Restriction
Authors: Stanley Jason , Gendler Szabó Zoltán
Published: December 2004

In this paper, we provide a comprehensive survey of the space of possible analyses of the phenomenon of quantifier domain restriction, together with a set of considerations which militate against all but our own proposal. Among the many accounts we consider and reject are the ‘explicit’ approach to quantifier domain restric‐tion discussed, for example, by Stephen Neale, and the pragmatic approach to quantifier domain restriction proposed by Kent Bach. Our hope is that the exhaustive discussion of this special case of context‐dependence will provide guidelines for how to decide, for an arbitrary case of context‐dependent discourse, whether it should be treated syntactically, semantically, or pragmatically.
Decreasing Numbers at Increasing Levels: An Investigation of the Gender Imbalance at NHH
Authors: Falkenberg Joyce
Published: December 2004

Gender imbalance is a highly discussed topic in Norway, where equity is the norm. At the Norwegian School of Economics and Business Administration (NHH) the issue of gender imbalance has been on the strategic agenda of the school for the past 12 years. Because these strategies have not resulted in the reduction of the gender imbalance that was expected, it is necessary to look for further explanations. Gender imbalance can result from hiring practices, turnover, or promoting policies. In this article the focus is on retaining women in the organization, and we draw on the literature from organizational attachment to uncover additional understanding of gender imbalance. The article reports the findings from an exploratory study of organizational attachment among the faculty at NHH. Findings indicate differences between male and female faculty members and PhD students on organizational commitment, on the value and expectation of job characteristics, on the suitability of the paradigm, and on alternative job possibilities.
Reconceptualizing Women's Paid Informal Work: Some Lessons from Lower‐Income Urban Neighbourhoods
Authors: Williams Colin C. , Windebank Jan
Published: December 2004

This article evaluates critically whether women's paid informal work is low‐paid market‐like work conducted for the purpose of economic gain. Drawing upon interviews with 400 households in UK lower‐income urban neighbourhoods, we show that only a small segment of the paid informal work conducted by women is of this character. The vast bulk is undertaken for and by friends, relative and neighbours under non‐market relations for reasons associated with redistribution and sociality. Given this finding, we thus conclude that a reconsideration is required of whether eradication alone is always the appropriate policy response.
The Interlocking of Gender with Nationality, Race, Ethnicity and Class: the Narratives of Women in Hotel Work
Authors: Adib Amel , Guerrier Yvonne
Published: December 2004

Whilst gender in the workplace is has been extensively researched, investigation into how gender interacts with other factors such as ethnicity and class has been less explicitly considered. This article explores the interlocking of gender with other categories such as class, ethnicity, race and nationality in the context of hotel work. It draws on the narratives of women describing their experiences of working in hotels. Findings from this empirically based examination suggest that gendered and other representations at work are not constructed as a process of adding difference on to difference, where categories are considered as separate and fixed. Instead, what emerges is a negotiation of the many categories shaping identities at work, which exist simultaneously and shift according to context.
Can Insider Power Affect Employment?
Authors: Díaz-Vázquez Pilar , Snower Dennis J.
Published: December 2004

Do firms reduce employment when their insiders (established, incumbent employees) claim higher wages? The conventional answer in the theoretical literature is that insider power has no influence on employment, provided that the newly hired employees (entrants) receive their reservation wages. The reason given is that an increase in insider wages gives rise to a countervailing fall in reservation wages, leaving the present value of wage costs unchanged. Our analysis contradicts this conventional answer. We show that, in the context of a stochastic model of the labor market, an increase in insider wages promotes firing in recessions, while leaving hiring in booms unchanged. Thereby insider power reduces average employment.
Senior Civil Servants and Bureaucratic Change in Belgium
Authors: Dierickx Guido
Published: December 2004

The Belgian civil service used to be a Weberian bureaucracy, with a strict division of labor between civil servants and politicians, administrative careers based on both seniority and partisan patronage, and a technocratic culture coupled with a high level of alienation from both politics and politicians. Administrative reform came in the wake of the constitutional reform that transformed unitary Belgium into a federal state with several governments, each with a civil service of its own. The fiscal crisis prompted them to look favorably on the promises of New Public Management (NPM). The new Flemish government was first to take advantage of this opportunity, as it had the financial resources, the tendency to refer to Anglo‐Saxon and Dutch examples, and the right political and administrative leadership.The staying power of these as yet precarious reforms depends on the continuity of political leadership, the establishment of an administrative culture matching the institutional innovations, and resistance to the endemic temptation to use them for partisan purposes.
Bureaucrats and Politicians in Britain
Authors: Wilson Graham K. , Barker Anthony
Published: December 2004

The distinctive relationship between bureaucrats and politicians in Britain has been much noted around the world and often used a model by reformers. However, both Conservative and Labour governments have displayed dissatisfaction with the bureaucracy and have made important changes in the “Whitehall model.” Some of these changes have reduced the degree to which British politicians have been unusually dependent on a career bureaucracy that is insulated from partisan politics.
Getting payments at Centrelink
Authors: Mackay Geraldene
Published: December 2004

This paper presents findings from a small qualitative study of tertiary students who were receiving income support payments from Centrelink. They are some of the millions of Australians receiving income support payments from Centrelink each year. The aim of the study was to explore and illuminate the experience of receiving income support payments. The findings indicate that people who may appear to have no problems accessing Centrelink may nevertheless undertake considerable efforts to receive their payments. These efforts involve practical tasks, intra and interpersonal processes and use of material resources. As many social work clients receive some sort of income support payment, these issues are relevant across social work settings.
Gender and professional identity: A qualitative study of social workers practising as counsellors and psychotherapists
Authors: Lewis Ione
Published: December 2004

This article presents an analysis of the interactions between gender and class in the career pathways of social workers practising as counsellors and psychotherapists. Gender is one of the strong patterns found in the empirical data generated by a qualitative study of the professional identity of practitioners in social work. Gender was found to have a strong influence on the career choices made by men and women in social work. Women in the sample have pursued career directions that continue to have a strong clinical focus, combined with other roles such as management, supervision and training. They are more likely to express the need to balance their working lives with the needs of their families. Men are more likely to single‐mindedly pursue careers in management and to express feelings of responsibility to provide for their families once children are born. However, the analysis of data also found that men were more likely to identify their family origins as working class, while women identify their family backgrounds as middle class. This patterning shows the complex interactions between gender and class in determining life outcomes. These differential pathways and work preferences need to be recognised and addressed to work towards more equitable outcomes for practitioners within social work, so that structural disadvantages on the basis of gender and class are challenged rather than replicated.
Association of single nucleotide polymorphisms in klotho with priapism in sickle cell anaemia
Authors: Nolan Vikki G. , Baldwin Clinton , Ma Qianli , Wyszynski Diego F. , Amirault Yvonne , Farrell John J. , Bisbee Alice , Embury Stephen H. , Farrer Lindsay A. , Steinberg Martin H.
Published: December 2004

The complications of sickle cell disease are probably determined by genes whose products modify the pathophysiology initiated by the sickle haemoglobin mutation. Priapism, one vaso‐occlusive manifestation of sickle cell disease, affects more than 30% of males with the disease. We examined the possible association of single nucleotide polymorphisms (SNPs) in 44 candidate genes of different functional classes for an association with the occurrence of priapism. One hundred and forty‐eight patients with sickle cell anaemia and incident or a confirmed history of priapism were studied, along with 529 controls that had not developed priapism. Polymorphisms in the KLOTHO gene (KL; 13q12) showed an association with priapism by genotypic [reference SNP cluster identifier number (rs)2249358; odds ratio (OR) = 2·6 (1·4–5·5); rs211239; OR = 1·7 (1·2–2·6)] and haplotype analyses [rs211234 and rs211239; OR = 2·3 (1·5–3·4)]. These findings may have broader implications in sickle cell disease, as KL encodes a membrane protein that regulates many vascular functions, including vascular endothelial growth factor expression and endothelial nitric oxide release.
Syndecan‐1 and angiogenic cytokines in multiple myeloma: correlation with bone marrow angiogenesis and survival
Authors: Andersen Niels Frost , Standal Therese , Nielsen Johan Lanng , Heickendorff Lene , Borset Magne , Sørensen Flemming Brandt , Abildgaard Niels
Published: December 2004

Angiogenesis is a complex process involved in the proliferation and metastasis of malignant tumours, and partly triggered by the secretion of various angiogenic factors by tumour cells or cells in the stromal environment. We investigated the correlation between bone marrow angiogenesis, estimated as microvessel density (MVD), and interleukin‐6 (IL‐6), basic fibroblastic growth factor (bFGF), hepatocyte growth factor (HGF) and syndecan‐1 in 67 patients with newly diagnosed multiple myeloma, and evaluated the prognostic value of these parameters. Circulating levels of IL‐6, bFGF, HGF and syndecan‐1 were significantly higher in patients than in controls. Moreover, in patients, bone marrow levels of bFGF, HGF and syndecan‐1 were higher than peripheral blood levels. Positive correlations were found between MVD and syndecan‐1 blood levels (r = 0·33,P = 0·017), syndecan‐1 bone marrow levels (r = 0·49,P = 0·046) and HGF blood levels (r = 0·36,P = 0·008) respectively. High MVD and high blood levels of IL‐6, HGF and syndecan‐1 were predictive of a shorter survival. In a multivariate survival analysis MVD and blood levels of IL‐6 retained independent prognostic significance, while in a survival analysis without MVD the peripheral blood levels of HGF and syndecan‐1 were strong independent prognostic factors.
Presence of anti‐kinectin and anti‐PMS1 antibodies in Japanese aplastic anaemia patients
Authors: Hirano Naoto , Butler Marcus O. , Guinan Eva C. , Nadler Lee M. , Kojima Seiji
Published: December 2004

While anti‐kinectin antibodies are frequently found in aplastic anaemia (AA) patients from the US (39%), we detected antibodies in only three of 30 (10%) of Japanese AA cases. Additionally, population differences in anti‐postmeiotic segregation increased 1 (PMS1) responses were seen, with detectable antibody in 10% Japanese and 0% US AA patients. In one of the Japanese AA patients with detectible anti‐kinectin antibodies, the autoantibody disappeared coincidentally with the partial resolution of pancytopenia. These results support the hypothesis that the epidemiology of AA is heterogeneous and suggest that anti‐kinectin autoantibody titre may serve as a surrogate maker for the disease activity of AA.
Gall initiation enhances the availability of food resources for herbivorous insects
Authors: Nakamura M. , Miyamoto Y. , Ohgushi T.
Published: December 2004

Insect herbivory may have not only negative but also positive plant‐mediated effects on other insect herbivores. We investigated plant‐mediated effects of the stem gall midge Rabdophaga rigidae on other insect herbivores through regrowth response of the willow Salix eriocarpa.

Gall initiation on current‐year shoots stimulated the development of lateral shoots, followed by a secondary leaf flush. Lateral shoots and upper leaves on galled shoots were less tough and had a higher water and nitrogen content.

Colonization rates by the aphid Aphis farinosa were significantly higher on galled shoots than on ungalled shoots, because this aphid frequently colonized lateral shoots.

Adults of two leaf beetles, Plagiodera versicolora and Smaragdina semiaurantiaca, were more abundant on galled than on ungalled shoots; they preferentially fed on young leaves produced during the secondary leaf flush.

Gall initiation positively affected aphids and leaf beetles by enhancing the availability of food resources as a result of the regrowth responses of S. eriocarpa. This indicates that the regrowth responses of plants to insect herbivory provide an important mechanism responsible for positive effects on other insect herbivores.
Long‐term patterns of leaf, shoot and wood production after insect herbivory in the Mountain Birch
Authors: Karlsson P. S. , Weih M.
Published: December 2004

The pattern of responses of adult trees of Mountain Birch (Betula pubescens ssp. czerepanovii) to an outbreak of a folivorous insect (Epirrita autumnata) causing ≈90% defoliation was studied over 8 years in a subarctic area in northern Sweden.

Tree recovery was monitored in terms of the numbers, area, mass and nitrogen content of leaves, the numbers of leaf‐carrying long and short shoots, and the widths of annual tree rings in stems.

The most prominent characteristic of defoliated trees was a threefold increase in the proportion of long shoots 1 year after defoliation. These shoots subsequently produced many new leaf‐carrying short shoots, resulting in shoot populations ≈50% larger than those of control trees. Thereafter the most strongly defoliated trees showed decreasing leaf area.

Defoliated trees produced more female catkins but fewer male catkins than control trees.

Released apical dominance did not result in any overcompensation in terms of growth or leaf area production. However, it presumably increased the rate of recovery from herbivory. For the most strongly defoliated trees, the benefits from increased production of long shoots was not sustainable.
Comparative fire ecology of tropical savanna and forest trees
Authors: Hoffmann William A. , Orthen Birgit , Nascimento Paula Kielse Vargas do
Published: December 2004

Fire is important in the dynamics of savanna–forest boundaries, often maintaining a balance between forest advance and retreat.

We performed a comparative ecological study to understand how savanna and forest species differ in traits related to fire tolerance. We compared bark thickness, root and stem carbohydrates, and height of reproductive individuals within 10 congeneric pairs, each containing one savanna and one forest species.

Bark thickness of savanna species averaged nearly three times that of forest species, thereby reducing the risk of stem death during fire. The allometric relationship between bark thickness and stem diameter differed between these two tree types, with forest species tending to have a larger allometric coefficient.

The height of reproductive individuals of forest species averaged twice that of congeneric savanna species. This should increase the time necessary for forest species to reach reproductive size, thereby reducing their capacity to reach maturity in the time between consecutive fires.

There was no difference in total non‐structural carbohydrate content of stems or roots between savanna and forest species, though greater allocation to total root biomass by savanna species probably confers greater capacity to resprout following fire.

These differences in fire‐related traits may largely explain the greater capacity of savanna species to persist in the savanna environment.
Differential phosphorus and nitrogen effects drive species and community responses to elevated CO2 in semi‐arid grassland
Authors: Grünzweig José M. , Körner Christian
Published: December 2004

Productivity of dryland communities is often co‐limited by water and nutrients. Since atmospheric CO2 enrichment induces water savings by plants, elevated CO2 and nutrients could interact to reduce growth limitation, irrespective of the direct influence of CO2 on photosynthesis. We studied CO2 effects in model communities from the semi‐arid Negev of Israel with 17 mostly annual C3 species at three CO2 concentrations and three nutrient treatments.

Community biomass increased at elevated (440 and 600 µL L−1) compared to pre‐industrial CO2 (280 µL L−1) by 34% on average in the low‐nutrient control, by 45% in the high P and by 50% in the high NPK treatment. Less evapotranspiration at elevated CO2 increased soil water content by 30–40% on average. Significant CO2–fertilization interactions indicated that plant responses to CO2 enrichment were constrained by nutrient availability.

Responses of biomass and water‐use efficiency (dry‐matter accumulation per cumulative evapotranspiration) to CO2 enrichment were non‐linear and were saturated at 440 µL L−1 at low nutrient and high P supply. CO2 effects were further increased up to 600 µL L−1 only under full NPK fertilization.

The overall CO2 effect on biomass depended on the differential response of plant functional groups, with the P‐dependent legume response dominating at low nutrient and high P supply, and the N‐dependent grass response dominating at high NPK. With the exception of grasses, species responded differently to combinations of CO2 enrichment and nutrient addition, even within functional groups.

Biomass production was co‐limited by CO2 and nutrients in this semi‐arid seasonal community, with both effects possibly mediated by water availability. Nutrient losses associated with desertification will thus diminish potential gains in biomass due to elevated CO2. Growth stimulation by CO2 enrichment beyond close‐to‐current concentrations will only be seen under nutrient‐rich conditions in semi‐arid and possibly other drought‐stressed grasslands.
Simulated carbon uptake for a canopy of two broadleaved tree species with contrasting leaf habit
Authors: Dungan R. J. , Whitehead D. , McGlone M. , Allen R. B. , Duncan R. P.
Published: December 2004

We used an environmentally driven, process‐based model to investigate the relative benefits of deciduous and evergreen leaves, in terms of net annual canopy carbon uptake, for a canopy of two tree species with contrasting leaf habit: deciduous Fuchsia [Fuchsia excorticata(J. R. Forst. and G. Forst) L. f.]; and annual‐evergreen Wineberry (Aristotelia serrataJ. R. Forst. and G. Forst, W. R. B. Oliv.).

Parameters for the model were derived from a year of measurements at a field site with a maximum leaf area index (L) of 5·4 m2 m−2, of which Wineberry and Fuchsia comprised 4·9 and 0·5 m2 m−2, respectively. Net annual C uptake (ANET; daily photosynthesis minus respiration at night) was 930 g C m−2, of which Wineberry and Fuchsia contributed 850 and 80 g C m−2, respectively. Canopy respiration at night (RN) accounted for 29 and 18% of daily uptake for Wineberry and Fuchsia, respectively. The model was used to simulate the effects of an evergreen phenology for both species. This increasedANETrelative to that estimated using the observed phenology by only 1% for Wineberry, and 4% for Fuchsia. This was attributable to increased net C uptake during winter with the evergreen phenology being offset by increasedRN, and reducedANETduring summer.

This comparison was repeated for sites spanning the natural range of Wineberry and Fuchsia across New Zealand. In terms of net C balance, the relative advantage of an evergreen phenology decreased with average winter temperature for both species, to the point where a deciduous phenology resulted in a higher value forANETfor Fuchsia at sites where frosts limited winter uptake.

Our simulations suggest that there is no clear advantage, in terms of annual C balance, for a deciduous or evergreen phenology at sites with relatively mild winters. In contrast, at sites where frost‐induced photoinhibition limits photosynthesis for overwintering leaves, a deciduous phenology results in a higher value ofANETfor species, such as Fuchsia, with leaves that are very active photosynthetically during spring and summer. The lack of deciduousness in the New Zealand flora may be due to the low number of tree species with such photosynthetic characteristics, and this may be attributable to the generally poor nutrient availability in forest soils.
Gender effects on the post‐facilitation performance of two dioecious Juniperus species
Authors: Verdú M. , Villar‐Salvador P. , García‐Fayos P.
Published: December 2004

Plant facilitation usually changes to competition as plants age. In dioecious plants, females should be affected more negatively than males by stressful conditions because of the greater costs of female reproduction.

We investigated the gender effects on the post‐facilitation performance of adult plants of two dioecious Juniperus species from the high mountains of eastern Spain: J. sabina L. acts as a nurse plant for J. communis L. We compared physiological (water potential, carbon isotope discrimination and nitrogen concentration), vegetative (shoot growth) and reproductive (number of male flowers, and number of fruits and seeds) characters of associated and non‐associated plants of both species, to test the hypothesis that this association represents a more stressful condition for females than for males because of the greater costs of female reproduction.

Despite their close phylogenetic relatedness, both species showed a distinct performance pattern after the facilitation phase. Association with the nurse plant reduced the growth and reproductive capacity of both genders in J. communis, the facilitated species. In contrast, the association with J. communis did not affect the fitness of the nurse plant, J. sabina, although in accordance with our hypothesis a gender effect was found on several physiological parameters. Thus J. sabina‐associated females had a more negative water potential and carbon isotope discrimination than the associated males, but there were no differences between genders when growing in isolation.

The consequences of the post‐facilitation interaction between the two long‐lived woody Juniperus species are asymmetrical: harmful for the facilitated species, but harmless for the nurse.

Gender had also asymmetrical consequences on some functional traits of the nurse – but not the facilitated – species.
Mosses mediate grazer impacts on grass abundance in arctic ecosystems
Authors: Van Der Wal R. , Brooker R.W.
Published: December 2004

Large herbivores have significant impacts on the structure and function of temperate and tropical ecosystems. Yet herbivore impacts on arctic systems, particularly the mechanisms by which they influence plant communities, are largely unknown.

High arctic vegetation, commonly overlying permafrost soils, is often moss‐dominated with sparse vascular plant cover. We investigated the potential influence of large herbivores on arctic plant communities via their impact on the depth of the moss layer, leading to warmer soils and potentially benefiting vascular plants.

We found that grazer impacts on moss depth, and subsequently soil temperature, may influence vascular plant abundance and community composition because of the observed positive but growth‐form‐specific response of vascular plants to soil warming, promoting grasses in particular.

We propose that the positive association of grasses and large herbivores in arctic moss‐dominated systems results from two simultaneously operating positive feedback loops. First, herbivore grazing and trampling reduces moss layer depth, increasing soil temperatures. Second, grasses benefit directly from grazers as a result of additional nutrients from faeces and urine. Additionally, the tolerance of grasses to grazing may enable grasses to expand despite the losses suffered from herbivory.
Does within‐population variation in egg size reduce intraspecific competition in Atlantic Salmon, Salmo salar?
Authors: Einum S. , Fleming I. A.
Published: December 2004

If phenotypes differ in habitat preferences there may be a decrease in intraspecific competition with increasing phenotypic variation, causing heterogeneous populations to perform better than homogeneous ones. Furthermore, if the relative performance of different phenotypes depends on environmental conditions, population heterogeneity may buffer populations against temporal environmental variation.

Here these hypotheses are tested using 10 experimental populations of juvenile Atlantic Salmon (Salmo salar L.) reared across a range of five different water discharges. Each population consisted of fish of identical parental origins to control for genetic differences among populations, but differed in body size heterogeneity owing to differences in egg size distributions.

No effect of population heterogeneity on final body size or dispersal rates was detected. Thus, egg size heterogeneity does not appear to influence the average level of intraspecific competition in Atlantic Salmon.

There was a strong positive effect of water discharge on body size, but no effects of phenotypic heterogeneity on variation in final body size among discharge levels. Thus, the relative growth performance of juveniles arising from different egg sizes may not change sufficiently with environmental changes for egg size variation to create a strong buffering effect against year‐to‐year variation in environmental conditions.
Increase of male reproductive components with size in an animal‐pollinated hermaphrodite, Narthecium asiaticum (Liliaceae)
Authors: Ishii H. S.
Published: December 2004

In animal‐pollinated plants, female function is expected to increase with size because increased pollen production leads to more competition for ovules by pollen grains from the same parent, and a large flower number results in increased geitonogamy and, in turn, increased pollen discounting. To date, many studies have supported this prediction.

In Narthecium asiaticum (Maxim), an animal‐pollinated plant, however, male reproductive components in flowers increased with raceme size whereas female reproductive components did not. This was mostly because of the similar trend for middle to upper flowers within racemes.

Height above ground for middle to upper flowers was associated with raceme size, and higher flowers attracted more pollinators. Accordingly, more pollen grains were removed from upper flowers in larger racemes. Furthermore, an increased number of flowers may not increase local mate competition and geitonogamy in this species because only a few flowers function as males at any one time, irrespective of raceme size.

This may be the reason why male reproductive components of upper flowers increased with size, even though N. asiaticum is an animal‐pollinated plant. Male reproductive components of lower flowers did not increase, probably because the height of lower flowers was not associated with raceme size.
Towards a self-consistent approach to palaeomagnetic field modelling
Authors: Khokhlov A. , Hulot G. , Carlut J.
Published: December 2004

Recent studies of the palaeomagnetic field behaviour over the past 5 Myr rely on statistical analysis of mainly directional data. However, the data are quite sparse and ill-distributed, and directional parameters are non-linear functions of the local field, rendering such statistical analysis non-trivial. Up to now these difficulties have usually been ignored or removed by relying on simplifications (linearization, neglecting internal correlations, etc.) that are unfortunately not justified if the field contains some amount of complexity.

The purpose of the present paper is to present a rigorous statistical forward approach to palaeomagnetic field modelling. Starting from a statistical model of the field defined in terms of the statistics of its Gauss coefficients (along the lines pioneered by Constable & Parker 1988), we show how such a model may be exactly tested against any given data set, either on a local regional or a global scale. A method to implement this approach is outlined and examples based on published models are provided.

In particular we focus on the treatment of directional data, for which the method is most relevant. The corresponding local probability density functions are derived and shown to be non-Fisherian, which we note may be a significant source of artefacts for standard mean-field modelling. Although the method we propose is already useful in its present state, some slight improvements are possible in order to account for noise in the data better.
On anelliptic approximations for qP velocities in VTI media
Authors: Fomel Sergey
Published: December 2004

A unified approach to approximating phase and group velocities of qP seismic waves in a transversely isotropic medium with vertical axis of symmetry (VTI) is developed. While the exact phase‐velocity expressions involve four independent parameters to characterize the elastic medium, the proposed approximate expressions use only three parameters. This makes them more convenient for use in surface seismic experiments, where the estimation of all four parameters is problematic. The three‐parameter phase‐velocity approximation coincides with the previously published ‘acoustic’ approximation of Alkhalifah. The group‐velocity approximation is new and noticeably more accurate than some of the previously published approximations. An application of the group‐velocity approximation for finite‐difference computation of traveltimes is shown.
Inversion of nuclear well‐logging data using neural networks
Authors: Aristodemou Elsa , Pain Christopher , De Oliveira Cassiano , Goddard Tony , Harris Christopher
Published: December 2004

This work looks at the application of neural networks in geophysical well‐logging problems and specifically their utilization for inversion of nuclear downhole data. Simulated neutron and γ‐ray fluxes at a given detector location within a neutron logging tool were inverted to obtain formation properties such as porosity, salinity and oil/water saturation. To achieve this, the forward particle‐radiation transport problem was first solved for different energy groups (47 neutron groups and 20 γ‐ray groups) using the multigroup code EVENT. A neural network for each of the neutron and γ‐ray energy groups was trained to re‐produce the detector fluxes using the forward modelling results from 504 scenarios. The networks were subsequently tested on unseen data sets and theunseeninput parameters (formation properties) were then predicted using a global search procedure. The results obtained are very encouraging with formation properties being predicted to within 10% average relative error. The examples presented show that neural networks can be applied successfully to nuclear well‐logging problems. This enables the implementation of a fast inversion procedure, yielding quick and reliable values for unknown subsurface properties such as porosity, salinity and oil saturation.
Simulation of full‐waveform log in saturated cracked formations using Hudson's approach
Authors: Kazatchenko E. , Markov M. , Mousatov A.
Published: December 2004

We study the propagation of elastic waves that are generated in a fluid‐filled borehole surrounded by a cracked transversely isotropic medium. In the model studied the anisotropy and borehole axes coincide. To obtain the effective elastic moduli of a cracked medium we have applied Hudson's theory that enables the determination of the overall properties as a function of the crack orientation in relation to the symmetry axis of the anisotropic medium. This theory takes into account the hydrodynamic mechanism of the elastic‐wave attenuation caused by fluid filtration from the cracks into a porous matrix.

We have simulated the full waveforms generated by an impulse source of finite length placed on the borehole axis. The kinematic and dynamic parameters of the compressional, shear and Stoneley waves as functions of the matrix permeability, crack orientation and porosity were studied. The modelling results demonstrated the influence of the crack‐system parameters (orientation and porosity) on the velocities and amplitudes of all wave types. The horizontally orientated cracks result in maximal decrease of the elastic‐wave parameters (velocities and amplitudes).

Based on the fact that the shear‐ and Stoneley‐wave velocities in a transversely isotropic medium are determined by different shear moduli, we demonstrate the feasibility of the acoustic log to identify formations with close to horizontal crack orientations.
The effect of orthorhombic anisotropy and its implication for oil recovery and reservoir exploitation
Authors: Assad Jamal M.
Published: December 2004

Results of an experimental study of shear‐ and compressional‐wave propagation in an orthorhombically anisotropic medium are presented. The experiments were performed on a physical model consisting of two sets of fractures. The first set consisted of orientated rubber inclusions simulating weak material‐filled cracks. The second set consisted of a system of closely spaced parallel fractures simulated by thin plates of epoxy resin, superimposed orthogonally on the first set. Three cases of fracture orientations within the model were identified and studied. Case 1 is analogous to a jointed fracture reservoir with one vertical set of fluid‐filled cracks or fractures and one non‐filled horizontal set. This case is referred to as JFV. Case 2 is analogous to a double fracture reservoir with one horizontal set of fluid‐filled fractures or cracks and one non‐filled vertical set. This is referred to as DFH. Case 3 is analogous to a double fracture reservoir with two vertical sets of fractures or cracks, with only one fluid‐filled. Case 3 is referred to as DFV. A pulse transmission method was performed on all three modelled cases along the three principal axes. A directional variation in the compressional‐ and shear‐wave velocities, as well as distinct shear‐wave splitting, was observed. The elastic constants for each case were determined and differences between them were noted and compared with the controlled results of both layered (transverse isotropy, TI) and vertically fractured (azimuthally anisotropic models, VF) media. The differences in elastic moduli and velocities indicate the potential of recognizing the different fracture orientations and suggest an approach to designing a method of drilling to further enhance oil recovery and reservoir exploitation.