bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitrogen metabolism in the ectomycorrhizal fungus Hebeloma crustuliniforme
Authors: QUORESHI ALI M. , AHMAD IFTIKHAR , MALLOCH DAVID , HELLEBUST JOHAN A. 
Published: April 2006

SUMMARYWith glucose as the carbon source, the ectomycorrhizal basidiomycete Hebeloma crustuliniforme (Bull. ex. Amans) Quel. utilizes nitrate, ammonium and amino acids as sources of nitrogen. Inoculated as a suspension of fine hyphae in such liquid media, the fungus expands rapidly, exhibiting a distinct exponential phase with a doubling time of 1–2 d and a maximum content of mycelial protein during the first 7 d of growth. Its growth when amino acids serve as sole carbon and nitrogen source is, however, less rapid, and requires several days of induction under these conditions. In H. crustuliniforme, assimilation of ammonium appears to be carried out primarily via the NADPH‐glutamate dehydrogenase (GDH) pathway. Its NADPH‐GDH levels in exponentially growing mycelia are several times greater than the apparent nitrogen assimilation rates of the mycelia. Its levels of glutamine synthetase activity in comparison are very small during the exponential period of growth. The greatest levels of NADH‐GDH are found in glucose‐grown cultures during the post‐exponential period, and in glucose‐free amino acid‐grown cultures during the active period of growth. This suggests a catabolic role for the NADH‐GDH. Aspartate aminotransferase and alanine aminotransferase in H. crustuliniforme are highly active during the exponential period of growth, and their concentrations are increased further in the presence of amino acids as sole nitrogen sources, suggesting a key role for these enzymes in interactions between pathways of amino acid metabolism and carbon metabolism in the fungus.
The effects of rind damage and regeneration on permeability of the apoplast in sclerotia of Sclerotinia minor
Authors: YOUNG NICOLA , ASHFORD ANNE E. 
Published: April 2006

summarySclerotia of Sclerotinia minor Jaggar have the ability to regenerate a new rind when the old rind is damaged before or after maturity. Regeneration involves growth of a completely new rind to cut off the exposed damaged surface. New, more or less spherical rind and cortical cells form by outgrowth of existing medullary hyphae. The new rind cells become pigmented over several days and new cortical cells contain reserves when the new rind has become fully pigmented. This process is most rapid in immature sclerotia but even in mature sclerotia, a new rind is fully regenerated within 8 d. Intact mature sclerotia exclude the apoplastic tracer sulforhodamine C but when the rind is damaged they become leaky to the fluorochrome. Regeneration of a new rind reduces permeability to sulforhodamine but the initial impermeable state is not fully regained, even when regeneration is complete. Sclerotia that have been damaged in the field, despite regeneration, might be more susceptible to external influences than those in which the rind has remained intact.
Evolutionary comparative analyses of the relationship between leaf structure and function
Authors: BEERLING D. J. , KELLY C. K. 
Published: April 2006

summaryWe have applied evolutionary comparative methods to control for phylogenetic relationships between species in order to determine if three recently proposed relationships between leaf structure and function are upheld, using a large database comprising a wide range of species from tropical and temperate ecosystems. The three hypotheses tested were: (i) leaf thickness is positively correlated with total stomatal density (adaxial and abaxial values summed); (ii) amphistomatous leaves (stomata present on the upper and lower surfaces) have a higher maximum stomatal conductance than hypostomatous (stomata on the lower surface only) leaves, and (iii) changes in the stomatal density on upper and lower leaf surfaces are regulated in a compensatory manner. The results showed that, contrary to several mathematical modelling studies, thicker leaves were not associated with more stomata either in species from lowland tropical rain forests or from central Europe. Amphistomatous leaves had a higher maximum stomatal conductance, indicating that one aspect of previous modelling work is correctly underpinned after accounting for relatedness. Finally, we found no evidence that the stomatal densities on upper and tower leaf surfaces are closely regulated. These three physiological traits are discussed with reference both to the modelling of leaf gas exchange and to plant function in relation to microclimate.
Allometric relations and growth in Pinus taeda: the effect of elevated CO2, and changing N availability
Authors: GEBAUER RENATE L. E. , REYNOLDS JAMES F. , STRAIN BOYD R. 
Published: April 2006

summaryLoblolly pine (Pinus taeda L.) seedlings were grown for 138 d at two CO2 partial pressures (35 and 70 Pa CO2) and four N solution concentrations (0.5, 1.5, 3.5 and 6.5 mM NH4NO3). Allometric regression analysis was used to determine whether patterns of biomass allocation among functionally distinct plant‐parts were directly controlled by CO2 and N availability or whether differences between treatments were the result of size‐dependent changes in allocation. Both CO2 and N availability affected growth of loblolly pine. Growth stimulation by CO2 at nonlimiting N solution concentrations (3.5 and 6.5 mM NH4NO3) was c. 90%. At the lowest N solution concentration (0.5 mM NH4NO3), total plant biomass was still enhanced by 35% under elevated CO2. Relative growth rates were highly correlated with net assimilation rates, whereas leaf mass ratio remained unchanged under the wide range of CO2 and N solution concentrations. When differences in plant size were adjusted apparent CO2 effects on biomass allocation among different plant parts disappeared, indicating that CO2 only indirectly affected allocation through accelerated growth. N availability, by contrast, had a direct effect on biomass allocation, but primarily at the lowest N solution concentration (0.5 mM NH4NO3). Loblolly pine compensated for N limitation by increasing specific lateral root length and proportional biomass allocation to the lateral root system. The results emphasize the significance of distinguishing size‐dependent effects on biomass allocation from functional adjustments made in direct response to changing resource availability.
Contents of free amino acids in Scots pine needles from field sites with different levels of nitrogen deposition
Authors: HUHN G. , SCHULZ H. 
Published: April 2006

summaryThe response of pine stands in areas with three different levels of nitrogen deposition was analysed on samples of the current year's needles. Each test area was subdivided into five test sites. Clear changes in the amounts of amino acids in relation to the nitrogen content of pine needles were found. Analyses were mainly focused on the amino acids glutamate (Glu), glutarnine (Gin) and those forming the urea cycle. The concentration of Gin increased significantly with response to increasing needle nitrogen content. Arginine (Arg) accumulated dramatically (up to 100‐fold) at high levels of needle nitrogen, but had the highest variation within the test sites. Ornithine (Orn) showed an increase only if the needle nitrogen content was very high. No clear relationship found in the case of Glu. Glutarnine and Arg are useful bioindicators of nitrogen pollution in pine stands.
Root colonization of mycorrhizal and non‐mycorrhizal pepper (Capsicum annuum) by Pseudomonas fluorescens 2–79RL
Authors: MARSCHNER PETRA , CROWLEY DAVID E. 
Published: April 2006

summaryThe survival and physiological status of a plant‐beneficial pseudomonad on the roots of mycorrhizal and non‐mycorrhizal pepper were examined. Pepper plants were grown for 20 d in split‐root microcosms with one side of the root system mycorrhizal with Glomus deserticola (GD) or Glomus intraradices (GI), while the other side was non‐mycorrhizal. Plants with both sides non‐mycorrhizal served as controls. The soil was inoculated with a bioluminescence‐marked strain, Pseudomonas fluorescens 2–79RL. Due to a ribosomal promoter that has been coupled to a lux gene cassette, P. fluorescens 2–79RL emits light in its exponential growth phase. Previous studies showed that the length of the lag phase of bioluminescence after transfer of soil‐cultured cells into rich medium can be used to assess the physiological status of this strain. After 20 d, shoot and root weight of the mycorrhizal plants in comparison with the control plants was decreased by 35% and 45% by GD and GI, respectively, indicating a high carbon cost of the mycorrhizal infection. Mycorrhizal infection was only 6% for GD, whereas it was 40 % for GI. Compared with the non‐mycorrhizal plants, GD affected P. fluorescens 2–79RL on the roots only on the side where the fungus was present, but had no effect on the non‐mycorrhizal side. On the mycorrhizal side, GD decreased the population density of P. fluorescens 2–79RL by 50 % and its physiological status by one order of magnitude. By contrast, GI decreased both the population density and the physiological status on the mycorrhizal and the non‐mycorrhizal side by one order of magnitude. On individual root segments, there was no correlation between the percentage mycorrhizal infection and the population density of P. fluorescens 2–79RL. It is concluded that some mycorrhizal fungi can reduce both the population density and the physiological status of certain bacterial groups in the rhizosphere.
Isozyme variation and somatic incompatibility in populations of the ectomycorrhizal fungus Suillus collinitus
Authors: EL KARKOURI K. , CLEYET‐MAREL J.‐C. , MOUSAIN D. 
Published: April 2006

summaryIsozyme variation and somatic incompatibility were investigated in order to study intraspecific genetic variation and to identify genets in natural populations of the ectomycorrhizal fungus Suillus collinitus (Fr.) O. Kuntze, Forty‐three isolates, obtained from basidiocarps collected in 11 forest sites under Pinus trees, were examined. Isozyme analysis indicated high intraspecific variation between isolates from the same location and from different locations. Phenetic analysis based on calculated dissimilarity values derived from isozyme banding patterns separated the isolates into two main groups (I and II) with 35% dissimilarity. A specific and highly active acid phosphatase isoform (ACP‐2) was detected in most group II isolates. Dikaryotic isolates displaying isozyme similarity coefficient of 100 % were found to be somatically compatible and were considered to originate from the same genet. The same genet was never found at more than two forest sites. This study showed a high correlation between the results of electrophoretic isozyme analysis and those of somatic incompatibility reactions. The results were discussed in terms of population biology.
Sulphur dioxide effects on fungi growing on leaf litter and agar media
Authors: DURSUN S. , INESON P. , FRANKLAND JULIET C. , BODDY LYNNE 
Published: April 2006

summaryRespiration of four decomposer fungi (Mycena galopus (Pers.) Kutnmer, Aureobasidium pullulans (de Bary) Arnaud, Phoma exigua Desm. and Cladosporium cladosporioides (Fres.) de Vries) growing on four species of leaf litter (Pinus sylvestris L., Picea sitchensis (Bongard) Carriére, Fraxinus excelsior L. and Corylus avellana L.) was inhibited by dry‐deposited SO2 in a laboratory experiment. Mycelial extension of the four fungi growing on four different agar media was inhibited by SO3 fumigation (40 nl l−1) in the laboratory, and media containing carbohydrates decreased the inhibitory effect of SO2 fumigation. Fumigation caused a statistically significant reduction in the mycelial extension of all species tested on tap‐water agar. These experiments demonstrate that decomposition of leaf litter is inhibited by environmentally realistic concentrations of SO2 and that the effect is exerted via inhibition of saprotrophic fungi.
Late Quaternary vegetational history at Navarrés, Eastern Spain. A two core approach
Authors: CARRION J. S. , DUPRE M. 
Published: April 2006

summaryPercentage and concentration pollen diagrams are presented for two cores (taken 5 m apart) at an upper Pleistocene and Holocene site at Navarrés (Valencia, eastern Spain). Chronological information is provided by an internally consistent radiocarbon dating series that extends from c. 20700 to 3075 yr BP. The results highlight the dangers of relying on a single core in interpreting the patterns of variation of particular taxa. Significant palynological differences, seemingly locational, are described between the two cores. The upper Pleistocene records accords well with the widely recognized European sequence of (a) upper Pleniglacial, (b) Bölling‐Allerod warm period, and (c) Younger Dryas crisis. However, the sequence does not show disruption of vegetation patterns following the commencement of the Holocene, and Pinus continues to be dominant up to c. 5500–6000 yr BP. Later, there is evidence for Quercus forest, mesophilous trees, and xerosclerophyllous Mediterranean vegetation, which is coincident with eutrophication of the study site. These vegetation changes are discussed in the context of anthropogenic disturbance by Neolithic people, competitive exclusion, and climatic change.
Antimicrobial defences in the wood of living trees
Authors: PEARCE R. B. 
Published: April 2006

summaryThe wood (xylem) in a living tree is protected from microbial attack by the secondary plant surface (periderm and rhytidome), which provides an effective barrier preventing the entry of most potential pathogens, and by constitutive and induced defence mechanisms in the bark (cortex and phloem). Although a few pathogens are able To penetrate these outer tissues directly, most xylem pathogens gain entry through wounds that expose this tissue and render it more vulnerable to attack. In functional sapwood, microbial colonization might be restricted by active defence mechanisms, or by passive microenvironmental restriction consequent upon the high water content and low availability of O2in healthy conductive xylem. These factors are not mutually exclusive: indeed, they may operate in concert in many host‐pathogen interactions. Sapwood lesions made by wood‐decaying fungi are characteristically bounded by multiccllular walls OT barrier zones (compartmentalization wall 4 barriers and reaction zones (column boundary layers)), which may function both as inhibitory or degradation‐resistant barriers to further pathogen spread, and as seals to maintain xylem function and prevent the drying and aeration that could predispose to further infection. A range of putative antimicrobial defence mechanisms contributing to the effectiveness of such barriers has been identified in sapwood tissues. This includes cell wall alterations, constitutive and induced antimicrobial compounds, necrotic responses of living cells and the deposition of gummy materials, often resinous or polyphenolic, at the host‐pathogen interface. Nutritional, environmental and anatomical features of living wood might also contribute to pathogen restriction. Although there might be differences in detail, the defences operating in gymnospenns and angiosperms are generally similar. Defence responses against a variety of pathogen categories also have much in common. Dynamic studies are crucial in elucidating the roles of the various components of the host‐pathogen interaction in the wood of living trees. A model for the protection and defence of xylem tissues in woody angiosperms is suggested, based largely upon results from dynamic studies of host‐pathogen interactions in the wood of sycamore (Acer pseudoplatanusL.).CONTENTSSummary203I.Introduction204II.Xylem pathogens205III.Bark the first line of defence206IV.Defence in functional sapwood207V.Defence in heartwood222VI.Dynamic aspects of the host‐pathogen interaction in wood223VII.Genetic control of resistance in xylem tissues224VIII.Antimicrobial defence in the living xylem of trees: towards a consensus model225Acknowledgements227References227
Analysis of stomatal CO2uptake by a three‐dimensional cylindrically symmetric model
Authors: VESALA T. , AHONEN T. , HARI P. , KRISSINEL E. , SHOKHIREV N. 
Published: April 2006

summaryA numerical model is introduced that solves the steady‐state diffusion equation for a single stoma and the mesophyll surrounding. This system has cylindrical symmetry, and diffusive transport of carbon dioxide in the gas phase is coupled with transfer in mesophyll alone with y photosynthetic sink rate and respiratory production rates. The mesophyll is treated as a continuously distributed liquid phase, and the photosynthetic rate is determined by the carbon dioxide concentration, the photosynthetic photon flux density and the chlorophyll concentration. Photorespiration is proportional to the photon flux density, and dark respiration is assumed to be constant. The model offers a rigorous way to investigate the roles of physics and geometrical structure in stomatal gas exchange. Lateral (radial) diffusion and differences between hypostomatous and needle‐like leaves are analysed with special attention. To vield realistic stomatal behaviour, the model requires that the diffusion coefficient describing mesophyllic transport must be somewhat larger than carbon dioxide diffusivity in pure liquid water. The mesophyllic carbon dioxide concentration slopes sharply towards a constant value as a function of distance from the surface of a sub‐stomatal cavity. The optimal placement of chlorophyll is close to the surface containing stomata.
The profusion of dark septate endophytic fungi in non‐ectomycorrhizal fine roots of forest trees and shrubs
Authors: AHLICH KARIN , SIEBER THOMAS N. 
Published: April 2006

summaryEndophytic fungi were isolated from surface‐sterilized non‐ectomycorrhizal fine roots of 14 shrub and forest tree species of the northern temperate zone. With the exception of three host species, between 70 and 100% of the roots of each host yielded endophytic fungi. Species diversity was tow. Thirty‐five taxa were found, nine of them in more than 1% of the 421 tree/shrub individuals examined. Dark septate endophytes (DSE; Mycelium radicis atrovirens‐complex dominated the fungal assemblages of coniferous and ericaceous hosts. About one fifth of the DSE sporulated after 1 yr of incubation at 4 °C and in darkness, and could be identified as Phiolocephala fortinii. could be isolated from a wide range of hosts and sites (Abies alba, Calltheria vulgaria, Fagus sylvatica, Picea abies, Pinus sylvestris and vaccinium murtillus in in Switzerland; Alnus rubra and Gaultheria Gaulteria shallon in Canada; Picea abies and Picea sylvestris in Germany. Pilots sylvestris in Finland). Thus, P. fortinii seems to be neither host‐ nor site‐specific. Four morphological types were recognized among the DSE‐isolates. Type 1 was distinctly different because its aerial mycelium was very sparse or absent. In contrast to other types, type 1 never sporulated. Thus, type I isolates probably belong to a separate taxon. Most isolates were of type 2. About one quarter of the type 2, type 3 and type 4 isolates sporulated and could fee identified as P. fortinii. Types 3 and 4 are supposed to be variants at type 2. The relative proportion of each type seemed to depend on the site, but a clear pattern of host or site preference could not be recognized. Differences between types in micromorphology of colonies grown on water afiar overlaid with cellophane sheets were minimal and therefore cannot he used for routine differentiation. The features of the DSE observed in root squashes corresponded well with those detected in synthesis experiments or pathogenicity vests with P. fortinii in other studies. In this study DSE were, never seen in roof tissues proximal to the innermost phellogen. Cryptosporiopsis radicicola was isolated most frequently form roots of F. sylvatica but constituted only;i minor component of the fungal assemblages of A. alba. Pic. abies. and Pin. sylvestris.
The dynamics of ectomycorrhizal infection of Shorea leprosula seedlings in Malaysian rain forests
Authors: SEE LEE SU , ALEXANDER I. J. 
Published: April 2006

summaryThe development of mycorrhizal infection on seedlings of the dipterocarp. Shorea leprosula (Miq.). was followed for 7 months after germination at three sites in West Malaysia. Arbuscular mycorrhizal infection was not observed, Seedling roots had well‐developed ectomycorrhizal sheaths, but no Hartig net, 20 d after germination, i.e. before the leaves had formed. By 2 months a range of ectomycorrhizal types with well‐developed Hartig nets were present. Twenty‐three types were recognized, of which 15 were common to alt three sites, and 20 to two sites. Individual seedlings never had more than five types and normally had line or two types only. The majority of ectomycorrhizas were formed by relatively few fungi and the six most abundant types at each site accounted for 77–92%, of the mycorrhizas. On the basis of the frequency of types (i.e. number of seedlings having mycorrhizas of a given type), and the number of times that a type contributed more than 40% of the mycorrhizas on a given seedling it was possible to recognize group of 12 dominant types. At each site new types were encountered at each harvest, and the number of types per harvest also increased. As well as fungi entering the mycorrhizal community as time progressed there was clear evidence that some fungi were lost or declined in relative abundance. Over the study period the level of infection fell at the two sites at which it was initially greatest. Although the community of mycorrhizal fungi was broadly similar at all three sites, overall level of infection, total number of types and number of types per seedling were highest at the site which appeared to have experienced the least disturbance and at which there were the greatest number of adult S. Ieprosula trees.
Effects of elevated CO2 and nutrient supply on the seasonal growth and morphology of Agrostis capillaris
Authors: NEWBERY R. M. , WOLFENDEN J. 
Published: April 2006

summaryResponses to elevated CO2 have been studied using an upland grass species, Agrostis capillaris L. The plants were grown in sand culture with a range of N, P and K concentrations, in ‘Solardome’ growth chambers with either ambient air or a CO2 concentration of 250μmol CO2 mol−1 above ambient The interactive effects of high CO2 and nutrient supply (in plant growth and morphology were monitored throughout the growing season. A. capillaris exhibited positive growth responses to enhanced CO2 even at limiting supplies of N and P. Moreover, greater shoot mass at elevated CO2 was attributed to disproportionate increases in leaf and tiller number, resulting in an increase in the average leaf number per tiller. However, total leaf area remained unaffected, indicating that leaf size was reduced. There was no evidence of any acclimation in the growth response of A. capillaris to additional CO2, even in N and P‐stressed plants. On the contrary, a stimulation in leaf production was observed later in the growing season.A consistent interaction was observed between N and P concentrations, whereby the response to one element was greater at higher concentrations of the other. In addition, there were indications of competition among the three elements for uptake at the root. These findings indicate the importance of multifactorial nutrient experiments in developing an understanding of the complex relationships during CO2 enrichment.