bluuebunny/crossref_metadata_2025_split huggingface dataset:
Field and laboratory experiments on net uptake of nitrate and ammonium by the roots of spruce (Picea abies) and beech (Fagus sylvatica) trees
Authors: GESSLER ARTHUR , SCHNEIDER STEPHAN , VON SENGBUSCH DOMINIK , WEBER PAUL , HANEMANN ULRIKE , HUBER CHRISTIAN , ROTHE ANDREAS , KREUTZER KARL , RENNENBERG HEINZ 
Published: March 2003

During the vegetation periods 1994 and 1995, net uptake of nitrate and ammonium by roots of adult spruce (Picea abies (L.) Karst) and beech (Fagus sylvatica L.) trees was studied at a field site exposed to high loads of N (‘Höglwald’, Germany). In addition, uptake experiments were carried out under controlled conditions with young spruce and beech trees grown at normal N supply.In the field, nitrate was not taken up by the roots of spruce trees in appreciable amounts. This was also true for beech except during September 1995. Apparently, beech trees was capable of taking up nitrate, but the environmental condition prevailing at the field site usually prevented net uptake. Net uptake of ammonium in both tree species showed a seasonal course, with maximum rates in mid summer. Rates of ammonium uptake by both species correlated with soil temperature at the field site.Laboratory experiments on the influence of root temperature on uptake of nitrate indicated that uptake rates at temperatures found in the field were low compared with the uptake capacity at optimum temperature. At temperatures of 10 and 15°C, frequently found in the soil at the field site, net uptake of nitrate by spruce and beech amounted to c. 16% and 11%, respectively, of maximum uptake at 25°C. By contrast, net uptake of ammonium at 10°C reached 73% and 31% of the maximum uptake for spruce and beech trees, respectively. Independent of temperature, rates of nitrate uptake were considerably lower than those of ammonium. In young spruce and beech trees, net uptake of nitrate was significantly inhibited by ammonium at nitrate∶ammonium ratios found in the soil solution at the forest site. Preincubation of roots of both species, with amino acids present in the phloem of adult trees at the field site, led to an increase in the amino acid pool in the roots. For spruce trees a correlation between inhibition of uptake of nitrate and enrichment of the roots with the amino compounds Glu, γ‐amino butyric acid (Gaba), Gln, and Asn was observed. In beech trees, enrichment of Asp and Gln in the roots correlated with a decrease in net uptake of nitrate. The results of laboratory experiments on the effects of temperature, the nitrate to ammonium ratio in the nutrient solution, and amino acid enrichment in the roots are discussed with special emphasis on the patterns of net uptake of ammonium and nitrate observed in the field.
Diversity of ectomycorrhizal fungi in Britain: a test of the species–area relationship, and the role of host specificity
Authors: NEWTON A. C. , HAIGH J. M. 
Published: March 2003

The host range of ectomycorrhizal (ECM) fungi in Britain was examined by compilation of a data matrix from published literature sources, based primarily on accounts of sporocarp associations with particular host genera. Information was gathered for 577 species of ECM fungi belonging to 51 genera, and 25 genera of host trees, representing the majority of ECM fungal species and host genera recorded in Britain.Pronounced variation was recorded in the number of ECM fungal species associated with different host genera, with over 200 species recorded with Betula, Fagus, Pinus and Quercus. There was a positive linear relationship (r2=0·47, P=0·007) between the number of species of ECM fungi associated with different host genera and the total area occupied by each tree genus in Britain (both values log‐transformed). There was also variation in the number of species of ECM fungi which were apparently specific to particular host genera, values ranging from zero (in 15 genera) to >40 in the case of Betula and Fagus. In total, 233 fungal species appeared to be specific to a single host genus (i.e. 40% of those surveyed). Comparison of the ECM mycota associated with different host genera by PCA accounted for 17% of the total variation, with genera belonging to the Fagaceae (Quercus, Fagus and Castanea) tending to cluster together, indicating a degree of overlap in their ECM associates. Exotic conifer species, which displayed a lower ECM diversity than would be expected from their distributional areas, were characterized by a high degree of overlap with the ECM associates of Pinus and Betula.These results indicate that the abundance of different genera of host trees and variation in host specificity could provide a basis for understanding patterns of diversity in ECM fungi within Britain.
Chitin and ergosterol combined to measure total and living fungal biomass in ectomycorrhizas
Authors: EKBLAD ALF , WALLANDER HÅKAN , NÄSHOLM TORGNY 
Published: March 2003

We have studied the chitin and ergosterol contents of ectomycorrhizal roots in three sets of experiments to evaluate them as indicators of fungal biomass. The first set of experiments showed that ageing had a marked effect on ergosterol concentrations. The ergosterol content of 7‐month‐old, brown, shrunken Pinus sylvestris L.–Paxillus involutus (Fr.) Fr. mycorrhizas was found to be only 10% of that found in white, turgid, 1‐ or 4‐month‐old specimens. This supports the hypothesis that the compound is a good indicator of living fungal biomass. Ageing had a lesser effect on chitin concentrations since the chitin levels found in 7‐month‐old mycorrhizas were still 60% of the levels found in 1‐ and 4‐month‐old specimens.Consequently, the chitin∶ergosterol ratio increased from about 14 to 19 in 1‐ and 4‐month‐old mycorrhizas respectively to about 110 in 7‐month‐old mycorrhizas. In the second set of experiments, we found that variation in plant growth had no effect on the chitin∶ergosterol ratio in whole root systems of either Alnus incana (L.) Moench or Pinus sylvestris mycorrhizal with Paxillus involutus. In the third set of experiments, we found a constant relationship between the two marker concentrations in 10‐month‐old root systems of Pinus sylvestris, regardless of fungal species involved, using Paxillus involutus, Piloderma croceum Erikss. & Hjorts and Suillus variegatus (Fr.) O. Kuntze as test organisms. Taken together, the results of this study suggest that both chitin and ergosterol give reliable, but different, relative measures of fungal biomass in mycorrhizal roots. Furthermore, we demonstrate that, in combination, the two chemical markers can be used to estimate both total and living fungal biomass (derived from the chitin∶ergosterol ratio).
Field measurements of root respiration and total soil respiration in an alder forest
Authors: Kutsch Werner L. , Staack Arne , Wötzel Jörg , Middelhoff Ulrike , Kappen Ludger 
Published: March 2003

Summary

• Variation in root respiration and total soil respiration measured in the field in an alder (Alnus glutinosa) forest is reported here, complementing previous studies of below‐ground carbon relations.
• A novel technique, involving minimum disturbance to the roots, was used to measure tree fine‐root respiration, while soil respiration was measured in an open system using infrared gas analysis. Calculations by process models of both rhizomicrobial, and bulk soil, respiration were compared with measurements of total soil respiration.
• The rhizomicrobial respiration rate was strongly temperature dependent, with the variation determined by fine root structural parameters. The data were used to calibrate a soil respiration model comprising mineralization and rhizomicrobial respiration submodels. The calculated annual rhizomicrobial respiration (1234 g m−2) matched the carbon balance of the alder trees calculated in earlier studies; however, the calculated total annual soil CO2 efflux (1754 g m−2) was very high compared with other European forest sites.
• The modelled total soil respiration fitted well to measured values; a changing groundwater table and modified carbon partitioning of the alder trees might account for deviations during early summer.
Carbon isotope discrimination by Sorghum bicolor under CO2 enrichment and drought
Authors: Williams D. G. , Gempko V. , Fravolini A. , Leavitt S. W. , Wall G. W. , Kimball B. A. , Pinter P. J. , LaMorte R. , Ottman M. 
Published: March 2003

Summary

Sorghum bicolor was exposed to free‐air CO2 enrichment (FACE) and drought at the Maricopa Agricultural Center, AZ, USA, in summer 1998. We predicted that bundle sheath leakiness (Φ) would be insensitive to FACE under well‐irrigated (wet) conditions, but would be lower in FACE compared with control‐CO2 treatments when irrigation was withheld (dry).
Leaf and air δ13C values and leaf pi/pa from gas exchange were measured to estimate carbon isotope discrimination (Δ) and F. Midday leaf water potential (Ψ) and photosynthetic rate were simultaneously measured to evaluate the influence of plant water status on Φ and the association between Φ and carbon gain.
Irrigation treatments affected Ψ, pi/pa, Δ and Φ in control CO2 and FACE rings. Differences in leaf Δ between wet‐ and dry‐treatment plots resulted from changes in Φ and to stomatal influences on pi/pa. FACE had very little effect on Ψ, Δ and Φ in wet‐treatment plots. However, Φ and Δ in dry plots were higher in control than in FACE rings.
FACE ameliorated the effects of drought on bundle sheath leakiness and Δ by reducing transpiration, prolonging soil water availability and enhancing plant water status. Direct effects of CO2 enrichment on C4 photosynthetic metabolism in Sorghum apparently are minimal and indirect effects depend on soil water supply.
Leaf conductance decreased under free‐air CO2 enrichment (FACE) for three perennials in the Nevada desert
Authors: Nowak Robert S. , DeFalco Lesley A. , Wilcox Carolyn S. , Jordan Dean N. , Coleman James S. , Seemann Jeffrey R. , Smith Stanley D. 
Published: March 2003

Summary

•  A common response of plants to elevated atmospheric CO2 concentration (CO2) is decreased leaf conductance. Consequently, leaf temperature is predicted to increase under elevated CO2.
•  Diurnal patterns of leaf conductance and temperature were measured for three desert perennials, the C3 shrub Larrea tridentata, C3 tussock grass Achnatherum hymenoides and C4 tussock grass Pleuraphis rigida, at the Nevada Desert FACE facility. Measurements were made on ambient and c. 550 µmol mol−1 CO2 plots through both a wet and dry year.
•  Reductions in conductance were 35%, 20% and 13% for Pleuraphis, Achnatherum and Larrea, respectively. Decreased conductance occurred throughout the day only for Pleuraphis. Both C3 species had smaller CO2 effects during dry periods than wet. Leaf temperature did not differ significantly between elevated and ambient CO2 for any species. Comparisons of blower‐control and nonring plots indicated that the FACE apparatus did not confound our results.
•  All three species exhibited decreased leaf conductance under elevated CO2, although reductions were not uniform during the day or among years. Nonetheless, leaf energy balance was only minimally changed for these microphyllous desert perennials.
Reduced photorespiration and increased energy‐use efficiency in young CO2‐enriched sorghum leaves
Authors: Cousins Asaph B. , Adam Neal R. , Wall Gerard W. , Kimball Bruce A. , Pinter Paul J. , Leavitt Steven W. , LaMorte Robert L. , Matthias Allan D. , Ottman Michael J. , Thompson Thomas L. , Webber Andrew N. 
Published: March 2003

Summary

To determine the response of C4 plants to elevated CO2 it is necessary to establish whether young leaves have a fully developed C4 photosynthetic apparatus, and whether photosynthesis in these leaves is responsive to elevated CO2.
The effect of free‐air CO2 enrichment (FACE) on the photosynthetic development of the C4 crop Sorghum bicolor was monitored. Simultaneous measurements of chlorophyll a fluorescence and carbon assimilation were made to determine energy utilization, quantum yields of carbon fixation (φCO2) and photosystem II (φPSII), as well as photorespiration.
Assimilation in the second leaf of FACE plants was 37% higher than in control plants and lower apparent rates of photorespiration at growth CO2 concentrations were exhibited. In these leaves, φPSII : φCO2 was high at low atmospheric CO2 concentration (Ca) due to overcycling of the C4 pump and increased leakiness. As Ca increased, φPSII : φCO2 decreased as a greater proportion of energy derived from linear electron transfer was used by the C3 cycle.
The stimulation of C4 photosynthesis at elevated Ca in young leaves was partially due to suppressed photorespiration. Additionally, elevated Ca enhanced energy‐use efficiency in young leaves, possibly by decreasing CO2 leakage from bundle sheath cells, and by decreasing overcycling of the C4 pump.
Carbohydrate metabolism in ectomycorrhizas: gene expression, monosaccharide transport and metabolic control
Authors: Nehls Uwe , Mikolajewski Sabine , Magel Elisabeth , Hampp Rüdiger 
Published: March 2003

SummaryEctomycorrhizas are mutalistic symbiotic associations formed between fine roots of higher plants, mostly trees, and a wide range of soil ascomycetes and basidiomycetes. It is commonly accepted that there is mutual benefit to the partners, due to the exchange of plant‐derived carbohydrates for amino acids and nutrients supplied by the fungus. While the major concepts of mycorrhizal functioning (exchange of nutrients and metabolites) were proposed in the 1960s, their verification at the molecular level started approximately 10 years ago. This review covers concepts at the molecular level concerned with the fungal carbohydrate supply in symbiosis. We discuss: strategies used by host plants to compensate (and perhaps restrict) carbohydrate drain to the fungal partner; fungal mechanisms that generate strong monosaccharide sinks in colonized plant roots (the formation of a strong carbohydrate sink is a prerequisite for efficient fungal carbohydrate support by the plant partner); and the impact of apoplastic hexose concentration on the regulation of fungal metabolism in symbiosis, since monosaccharides not only serve as nutrients but also as a signal that regulates gene expression.
Community ecology of ectomycorrhizal fungi: an advancing interdisciplinary field
Authors: Dahlberg Anders 
Published: March 2003

SummaryA long‐term goal of community ecology is to identify spatial and temporal factors that underlie observed community structures. Ultimately, ecologists seek to relate community patterns to ecosystem processes and functions. Since the mid 1990s, ectomycorrhizal (ECM) research has been equipped with tools to identify and fully quantify the taxonomic diversity in below‐ground ECM fungal communities in detail and address such questions. Many of the most important functions of terrestrial ecosystems, as well as interactions, between plants take place below ground and mycorrhizal fungi are among the key players in soil ecology. Here the rapidly increasing knowledge of ECM fungal community ecology is reviewed and the prospects discussed for elucidating processes that structure ECM fungal communities and the way in which such knowledge might be integrated with, and advance, the understanding of plant ecology and ecosystem processes.
PEP carboxylase kinase is a novel protein kinase controlled at the level of expression
Authors: Nimmo Hugh G. , Fontaine Véronique , Hartwell James , Jenkins Gareth I. , Nimmo Gillian A. , Wilkins Malcolm B. 
Published: March 2003

SummaryPhosphoenolpyruvate (PEP) carboxylase plays a number of key roles in the central metabolism of higher plants. The enzyme is regulated by reversible phosphorylation in response to a range of signals in many different plant tissues. The data discussed here illustrate several novel features of this system. The phosphorylation state of PEP carboxylase is controlled largely by the activity of PEP carboxylase kinase. This enzyme comprises a protein kinase catalytic domain with no regulatory regions. In many systems it is controlled at the level of expression. In C4 plants, expression of PEP carboxylase kinase is light‐regulated and involves changes in cytosolic pH, InsP3 and Ca2+ levels. Expression of PEP carboxylase kinase in CAM plants is regulated by a circadian oscillator, perhaps via metabolite control. Some plants contain multiple PEP carboxylase kinase genes, probably with different expression patterns and roles. A newly discovered PEP carboxylase kinase inhibitor protein might facilitate the net dephosphorylation of PEP carboxylase under conditions in which flux through this enzyme is not required.
Heterotrimeric G‐proteins in plant cell signaling
Authors: Millner P. A. 
Published: March 2003

SummaryHeterotrimeric G‐proteins, which couple cell surface receptors with internal effectors, are evident in all eukaryotes. Their operation involves receptor activation, GTP/GDP exchange and modulation of effector activity; deactivation occurs by an intrinsic GTPase activity. Structurally, G‐proteins comprise three dissimilar subunits; Gα, Gβ and Gγ. The Gα subunit consists of an α‐helical and a GTPase domain, the latter is responsible for interaction with Gβγ, receptor and effector. Gβ and Gγ form a tightly associated heterodimer which can also modulate effector activity when released by the activated Gα. Genome sequence and other data suggest that, in plants, there are several (~8–10?) Gα, one or two Gβ and one Gγ. These proteins are expressed throughout the plant, mainly in the plasma membrane and endoplasmic reticulum. In vivo, there is strong evidence for G‐protein control of ion channels, particularly K+, in the response pathways to fungal and bacterial pathogens as well as in some aspects of gibberellin, abscisic acid and auxin signaling pathways. Finally, future prospects for understanding plant G‐protein linked signaling will rely on new and emerging technologies; these include antisense suppression, gene knockouts, yeast two‐hybrid and phage display molecular approaches, intracellular immunization using recombinant single chain antibodies and expression of peptide encoding minigenes.
Vernalization response of wild chickpea
Authors: Abbo S. , Lev‐Yadun S. , Galwey N. 
Published: March 2003

Summary• Response to low temperature during early growth in cultivated chickpea (Cicer arietinum) and its wild progenitor C. reticulatum was investigated to clarify the evolutionary processes under domestication in this crop.• Parental lines and their F2 and F3 progeny were exposed to cold treatment (4°C) for 30°d after seed imbibition and compared with controls.• Cold treatment caused a 19‐d advance in flowering time in wild chickpea, but only a 3‐d advance in cultivated chickpea. It also promoted apical dominance of the main stem of the wild chickpea, whereas apical dominance was constitutive in the cultivated type. F3 progeny showed significant genetic variation affecting the response of flowering time to low temperature. We suggest that selection against alleles conferring vernalization requirements was a major step in the evolution of cultivated chickpea. The reduced low‐temperature response was fundamental both for the ancient conversion of chickpea from an autumn‐ to a spring‐sown crop (‘summer crop’) in west Asia, and for its spread into the lower‐latitude regions of India and east Africa.• Attempts to improve yield and/or resistance to biotic and abiotic stresses through introgression with wild chickpea species carry the risk of reintroducing vernalization sensitive alleles into the cultigen.
Extensive tubular vacuole system in an arbuscular mycorrhizal fungus, Gigaspora margarita
Authors: Uetake Y. , Kojima T. , Ezawa T. , Saito M. 
Published: March 2003

Summary• A tubular vacuolar system is reported here for the first time in living hyphae of Gigaspora margarita, an arbuscular mycorrhizal fungus, during various phases in the development of a symbiotic relationship with onion (Allium cepa) seedlings.• Germ tubes, extraradical hyphae and intercellular hyphae were labeled with Oregon Green 488 carboxylic acid diacetate and observed by laser scanning confocal microscopy. Emphasis was placed on the relationship between the shape of vacuoles and the presence of cytoplasmic streaming.• In germ tubes, labeled vacuoles showed a variety of profiles, including spherical and tubular (< 0.5 µm diameter), with various compositions of these shapes along the length of the germ tubes. The tubular vacuoles rarely interconnected with spherical vacuoles and often formed longitudinally oriented, elongated bundles. The tubular vacuolar system appeared to be associated with cytoplasmic streaming, whereas spherical vacuoles were not. Tubular vacuoles were observed in all regions of the germ tubes and were also observed in both extraradical and intercellular hyphae.• The results question the hypothesis that discrete vacuoles may be involved in the translocation of polyphosphate along hyphae of arbuscular mycorrhizal fungi.
Occurrence of tetraploid and hexaploid cytotypes between and within populations in Dianthus sect. Plumaria (Caryophyllaceae)
Authors: Weiss Hanna , Dobeš Christoph , Schneeweiss Gerald M. , Greimler Josef 
Published: March 2003

Summary

The occurrence of both tetraploid and hexaploid cytotypes within and between populations of several species of Dianthus
section
Plumaria was analysed.
Chromosome numbers for 13 populations of eight taxa are presented together with a thorough compilation of previously published data.
Most of the taxa are polyploids (tetraploids and hexaploids). Three groups can be distinguished: (1) only one ploidy level within a taxon; (2) more than one ploidy level, but only single cytotypes within a population; and (3) populations with a cytotype mixture. From some populations, reported earlier to contain tetraploids, we found only hexaploid individuals. Hexaploids occur over the whole range of polyploid taxa, revealing no geographical pattern.
Polyploidy is very likely the result of autopolyploidization, at least for the hexaploid cytotypes, which formed many times independently and occur sympatrically with tetraploids. Most of the populations with mixed cytotypes represent primary hybrid zones. It is not yet possible to decide whether directional (one cytotype will become extinct in the longer term) or balanced selection (both cytotypes can coexist) is acting in those populations.
The nature of value created by UK online grocery retailers
Authors: Bevan Julia , Murphy Ruth 
Published: March 2003

AbstractThe UK retail environment is extremely competitive, forcing retailers to constantly develop and enhance both their offerings and their formats. Probably the most significant changes taking place are coming from not the products being sold themselves, but rather when, how and where they are being sold. For example, new technologies such as the Internet, CD‐Roms, electronic kiosks and digital television are opening up new opportunities for retailers through remote purchasing and delivery. While a number of large retailers have made heavy investments into electronic retailing, such as Arcadia, Marks & Spencer, Tesco and Sainsbury, it is uncertain how they are going to use this technology to gain competitive or market advantages. Given the media attention which technologies such as the Internet has attracted, there is the danger that businesses may adopt an unfocussed use. This report identifies and evaluates the ways in which major UK grocery retailers are using the Internet to create value for their users over and above that which is offered by bricks and mortar stores. Web sites of three grocery retailers were evaluated via preselected criteria in order to assess how they created value for their customers. Applying Holbrook’s typology of consumer value, the findings of the research suggest that each of the retailers surveyed are similar in terms of the nature of the value they have created for consumers online, these being value‐as‐convenience and value‐as excellence.