bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature sensitivities of Festuca arundinacea Schreb. and Dactylis glomerata L. ecotypes
Authors: THOMAS HOWARD , STODDART JOHN L. 
Published: April 2006

summaryThe thermal responses of leaf growth and senescence were measured in four populations of Festuca arundinacea Schreb. and three of Dactylis glomerata L. with a range of geographical origins. Leaf extension was quantified by fitting logistic curves to lengths measured for up to 120 d in controlled environments at 20 °C or after transfer to 5 °C at emergence of the fourth leaf. Electronic position transducers were employed to observe rapid adjustments in leaf elongation rate in response to changes in the temperature experienced by the growing zone. Leaf segments were incubated in darkness on a thermal gradient bar giving a range of temperatures between 0 and 20 °C, and chlorophyll and protein were determined after 4 d of senescence. For each process, temperature sensitivities were determined as 010, to give a profile of thermal response for each ecotype. Correlations between processes across ecotypes enabled possible relationships between temperature perception mechanisms to be identified. In their responses to chilling temperatures, mean extension rates measured over a period of one or more plastochrons were not closely related to short‐term rates. There was a significant negative correlation between chlorophyll stability in excised leaf tissue and mean long‐term extension rates. In general, ecotypes from the coldest habitats were the most sensitive to low temperature inhibition.
Structural changes and permeability of ivy (Hedera helix L.) leaf cuticles in relation to leaf development and after selective chemical treatments
Authors: VIOUGEAS M. A. , ROHR R. , CHAMEL A. 
Published: April 2006

summaryThe fine structure of ivy leaf cuticles was investigated as a function of leaf development before and after cuticle isolation as well as after selective extraction of cuticle components. Cuticle mass increased with increasing age from 234°3 to 539.1 μg cm−2 Waxes increased from 12.3 to 18.6%, of cuticle mass from young to old leaves. However, percentages of cutin and non‐lipid constituents did not vary significantly with leafage. They represented approx. 58 and 26%, of the cuticle mass, respectively. Cuticle thickness determined from electron and light microscopy increased 12–fold during leaf growth to reach 4.25 μm for mature leaves. Transmission electron microscopy of transverse sections of non‐isolated and isolated cuticles showed an outer lamellate zone gradually merging from an inner reticulate zone the thickness of which increased with leaf growth. The lamellate zone appeared very early (in vitro unexpanded leaf) and was characterized by a constant thickness (0.2 μm). Cuticle lamellation seemed to disappear after extraction of soluble cuticular wax, which confirmed intracuticular wax localization in lamellae. Electron‐dense fibrillae observed in the reticulate zone disappeared after acid hydrolysis showing that they are made of non‐lipid components. X‐ray diffraction confirmed the presence of crystalline structures and revealed a cuticle disorganization alter wax extraction. Permeability measurements showed an increase rather than a decrease in glyphosate and isoproturon diffusion through cuticles with increasing leafage, suggesting that the main barrier to diffusion is the outer lamellate zone. A considerable increase in isoproturon penetration through cuticles resulted from the wax extraction, demonstrating the major role of wax in the control of cuticular permeability to this herbicide.
Changes in quercetin concentration in onion (Allium cepa L.) owing to location, growth stage and soil type
Authors: PATIL B. S. , PIKE L. M. , HAMILTON B. K. 
Published: April 2006

summaryA study with onion investigated the variation in the concentration of the potentially anticarcinogenic flavonol, quercetin owing to location, soil type and growth stage. Seven genotypes grown at two locations were analysed for aglycone and total quercetin concentration by reverse‐phase high‐performance‐liquid‐chromatography (RP‐HPLC). Out of seven genotypes investigated, four showed significant differences (P= 0.05) in total quercetin concentration between two locations. In 1993, ‘Texas Grano 10I5Y’ (TG1015Y) bulbs collected at five growth stages were analysed for quercetin concentration by RP‐HPLC. Quercetin concentration in ‘TG1015Y’ at different growth stages showed slight differences. Furthermore, quercetin concentration in bulbs harvested at second growth stage (23 March) was significantly (P= 0.05) greater than at the first growth stage (23 March). A slight difference in total quercetin concentration due to soil was noticed. This study shows that the site of growth of union is a major environmental factor in determining quercetin concentration but soil type and growth stage are not important.
The use of an unenclosed field fumigation system to determine the effects of elevated ozone on a grass–clover mixture
Authors: WILBOURN S. , DAVISON A. W. , OLLERENSHAW J. H. 
Published: April 2006

summaryA mixture of Trifolium repens L. (var. Grasslands Huia) and Lolium perenne L. (var. Melle) was established in an area with low ambient ozone concentrations and exposed to episodes of ozone using a simple, unenclosed field fumigation system. Control plots were exposed to ambient air. There were two cutting frequencies to simulate grazing and silage production respectively. This paper reports on the performance of the system and the effects on yield and species composition in the first year of fumigation.The system operated satisfactorily when the wind speed was between 1 and 5 m s−1. When the wind dropped suddenly below 1 m s−1there were short periods with high concentrations but these events were rare and did not last more than a few minutes. Above 5 m s−1there was lateral downwind spillage of ozone and at higher wind speeds it was not possible to maintain the target concentration of 50–70 nl 1−1. The plots were fumigated only when the weather was suitable for ozone formation and when the wind speed was stable. Because the weather was poor, fumigation was restricted to 22 d between July and September. The mean 4–7 h concentrations were 50–70 nl l−1. Seven‐hour mean ambient concentrations over the same period were 10–28 nl 1−1.There were significant effects of ozone on yield and herbage composition. The effects varied between harvests, probably because of differences in the timing of cutting relative to the episodes, and to the differences in phenology between the species. Most of the loss of yield was due to effects on Trifolium, which was much more sensitive than Lolium. There was a persistent effect of ozone on the stolon density of Trifolium which lasted into the following year. It is suggested that this arose because the clover replaced damaged leaves very quickly, maintaining the canopy at the expense of the stolons. Persistent effects on stolons might lead to poorer winter survival and lower nitrogen fixation. Gaps in the sward as a result of loss of Trifolium might allow rapid weed invasion. There was no interaction between cutting frequency and ozone, which may have been due to the fact that the poor summer restricted the number of cuts and therefore decreased the difference between the two cutting frequencies.
Variation in susceptibility and tolerance within and between populations of Tussilago farfara L. infected by Coleosporium tussilaginis (Pers.) Berk.
Authors: DE NOOIJ MARIANNE P. , PAUL NIGEL D. , AYRES PETER G. 
Published: April 2006

summaryQuantitative variation in susceptibility to infection by the rust Coleosporium tussilaginis, and in reduction in growth owing to the infection, were determined in 30 clonally propagated genotypes of Tussilago farfara sampled from three geographically isolated sites, Arnhem (The Netherlands), Lancaster and Sheffield (both UK). Populations, and genotypes within populations showed no significant variation in intensity of disease after artificial inoculation under ideal conditions with a fungal isolate collected from the Lancaster population. By contrast, significant differences between and within populations were observed after natural secondary infection by spores produced from the artificially inoculated plants. Genotypes differed considerably in the reduction in growth caused by the infection, but this was not correlated with the extent of symptoms shown by the plants. Low resistance was associated with high tolerance, as in the Lancaster and Sheffield populations, while high resistance was associated with low tolerance, as in the Arnhem population. The evolutionary significance of these associations is discussed.
Phosphorus and carbon budgets: mycorrhizal contribution in Hyacinthoides non‐scripta (L.) Chouard ex Rothm. under natural conditions
Authors: MERRYWEATHER JAMES , FITTER ALASTAIR 
Published: April 2006

summaryThe extent of host benefit from arbuscular mycorrhiza (AM) in terms of phosphorus (P) assimilation under natural conditions has rarely been demonstrated or quantified. An apparently obligately mycorrhizal host, Hyacinthoides non‐scripta (L.) Chouard ex Rothm., was selected and, throughout the season September‐July 1989–90, entire clones were collected from a field site at frequent intervals without experimental modification of the host, its mycosymbiont or their environment. In a concurrent glasshouse experiment, sand‐cultured non‐mycorrhizal plants given a nutrient solution containing a supply of P were unable to assimilate sufficient to maintain tissue P content.We provide correlative evidence of mycorrhizal behaviour in an undisturbed, natural ecosystem by demonstrating the temporal coincidence of root colonization by mycorrhizal fungi and the inflow of phosphorus in adult H. non‐scripta. Annual carbon (biomass) and phosphorus budgets are described. Carbon was reallocated from the resting bulb, first for root production and, later, to developing leaves and inflorescences. A similar pattern was observed in P allocation. A substantial amount of P was lost in seed, leaves, roots and scapes shed at the end of a season, when bulb biomass had increased, but P content had not.
Interactions between native prairie grasses and indigenous arbuscular mycorrhizal fungi: implications for reclamation of taconite iron ore tailing
Authors: NOYD ROBERT K. , PFLEGER F. L. , RUSSELLE M. P. 
Published: April 2006

summaryIn a glasshouse experiment using coarse taconite iron ore tailing as the substrate, we examined interactions between the warm‐season grasses Andropogon gerardii (big bluestem) and Schizachyrium scoparium (little bluestem), and the cool‐season grass Elymus canadensis (Canada wild rye), and indigenous arbuscular mycorrhizal (AM) fungi from an adjacent fine tailing basin. Shoot dry mass (DM), P uptake, shoot P concentration, root DM, root length, spore density, percentage root length colonized, and length of external AM fungal hyphae were measured over a gradient of phosphate availability. Andropogon gerardii was highly dependent and responsive to inoculation at low P, whereas inoculation had no significant effect on the growth of 5. scoparium. Root DM and root lengths of both warm‐season grasses were unaffected by mycorrhizal inoculation. Elymus canadensis was responsive only at the lowest P level and not dependent on mycorrhizas; in fact, shoot DM, P uptake, root DM and root lengths were all greater in control than inoculated plants at moderate P levels. Despite a growth suppression, colonized root lengths for E. canadensis were approximately five times longer than warm‐season grasses at low P levels, making it suitable as an early succession species for increasing mycorrhizal inoculum potential and thus enhancing the successful reclamation of coarse tailing deposits by more persistent, mycorrhizal‐dependent species.
Influence of potassium nutrition on germinability, abscisic acid content and sensitivity of the embryo to abscisic acid in developing seeds of Sorghum bicolor (L.) Moench
Authors: ARNOLD R. L. BENECH , FENNER M. , EDWARDS P. J. 
Published: April 2006

summaryPre‐harvest sprouting in maturing seeds of Sorghum bicolor (L.) Moench is a major problem in the cultivation of this crop plant. The influence of potassium nutrition on germinability, abscisic acid (ABA) content and embryo ABA sensitivity in its developing seeds was investigated. Plants were grown in sand culture under three different potassium treatments: K1 (control), K2 (one third of the control potassium supply), and K3 (one ninth of the control potassium supply). Reduced potassium increased the germinability of developing seeds during the late stages of maturation (31 and 36 days after pollination, DAP), particularly in K2 grains. These changes in seed germinability were paralleled by a reduced ABA content in the seed and by a lower embryonic sensitivity to ABA. The ABA content of K2 intact grains peaked at 25 DAP and then decreased sharply, being 30–50% lower than that in the controls at 31 and 36 DAP. ABA content in the control gains peaked later in the developmental period (at 31 DAP). By contrast K3 grains had a remarkably constant ABA content during most of the developmental period (20–36 DAP). Sensitivity to ABA was markedly reduced in the embryos from both the low potassium treatments, particularly when tested at an ABA concentration of 5μM. The data indicate that potassium supply influences germinability, ABA concentrations and embryo ABA sensitivity in developing seeds in this species.
Fungal slime and its role in the mycorrhizal amelioration of zinc toxicity to higher plants
Authors: DENNY H. J. , RIDGE I. 
Published: April 2006

summaryThe degree of sliminess of a range of fungal isolates which form endomycorrhizas with Calluna vulgaris L. was investigated and related to their performance in the presence of potentially toxic concentrations of zinc. Some fungal isolates possess, to a greater or lesser extent, a mass of loosely adherent slime (LAS). The amount of this was proportional to the ability of the fungal mycelium to take up zinc from solution, the zinc tolerance of the fungal isolates, and the amount of growth enhancement exhibited by the associated C. vulgaris plants in the presence of potentially toxic concentrations of zinc. Furthermore the amount of LAS was inversely proportional to the concentration of zinc found in the shoots of the associated C. vulgaris plants. These observations support the hypothesis that LAS plays a central role in removing zinc ions from solution, removal which in turn determines the zinc tolerance of the fungus itself and the degree of amelioration of zinc toxicity to the host plant.
Holocene vegetation history and human impact at Bryn y Castell, Snowdonia, north Wales
Authors: MIGHALL T. M. , CHAMBERS F. M. 
Published: April 2006

summaryThree radiocarbon‐dated pollen diagrams are presented from Holocene peat and lake deposits in Snowdonia, close to the Late Iron Age/Romano‐British ironworking hill‐tort of Bryn y Castell, Gwynedd, in upland north Wales. This paper discusses pollen, charcoal and peat‐stratigraphic evidence for major local vegetation changes and for the development of the surrounding cultural landscape during the last 10000 radiocarbon yr. Pollen data from one of the sites (BYC 2) provided a vegetational record for most of the Holocene. The early part of the sequence suggests an oligotrophic lake in a landscape that is being colonized by birch‐pine woodland; later, mixed deciduous woodland surrounds an infilling lake basin. Dating of peat deposits at two of the sites (BYC, BYC H) indicated that their pollen records commenced between 5500 and 5000 yr BP. By this time, the lake basin was fringed by alder carr. There followed a gradual and then, c. 2700 yr BP, a more abrupt decline in woodland, such that, by the end of the Bronze Age and with the basin largely terrestrialized, the local landscape became dominated by mire vegetation communities, which have persisted to the present. Human activity seems to have been a major factor in the loss of woodland cover. Although there is some circumstantial evidence for earlier phases of human disturbance at BYC 2, human activity becomes increasingly apparent from c. 5000 yr BP. During the mid Holocene, the impact of Neolithic and early‐ to mid‐Bronze Age cultures appears to be characterized by temporary woodland clearances, for arable and pastoral agriculture. By c. 2700 yr BP the majority of woodland cover seems to have been permanently removed from the landscape, but as there is scant archaeological evidence for late Bronze Age cultures in this part of Snowdonia, other factors, especially climate change, could be implicated. During the late Holocene, especially during part of the late Iron Age and Romano‐British period, remaining local stands of woodland seem to have been exploited for iron smelting, although the overall impact of ironworking was limited.
Quantitative imaging of chlorophyll fluorescence
Authors: ROLFE STEPHEN A. , SCHOLES JULIE D. 
Published: April 2006

summaryA computer‐controlled video system is described where images of chlorophyll fluorescence from oat (Arena saliva L.) leaves are captured throughout an induction curve. The fluorescence parameters φ11 and ΔFm/F'm which represent photosystem II photochemical efficiency and non‐photochemical quenching respectively are calculated from images taken under actinic and saturating illumination. They are compared with the equivalent parameters determined from simultaneous measurements made with a non‐imaging modulated fluorimeter. The leaves are imaged in the chamber of an infra‐red gas analyser, allowing the relationship between the fluorescence parameters and CO2 assimilation to be determined. Under a series of illumination conditions and partial pressures of CO2, the values of φ11 determined by image analysis are in close agreement with those obtained by modulated fiuorimetry and are linearly related to CO2 assimilation. The values of ΔFm/Fm determined by image analysis are linearly related to those obtained by modulated fluorimetry but the absolute values differ between the two systems. The video system described can be used to examine quantitative changes in fluorescence parameters in a heterogeneous system.
Uptake of15NO2by sunflower (Helianthus annum) during exposures in light and darkness: quantities, relationship to stomatal aperture and incorporation into different nitrogen pools within the plant
Authors: SEGSCHNEIDER HANS‐JOSEF , AND JÜRGEN WILDT , FÖRSTEL HILMAR 
Published: April 2006

summaryExposures of sunflowers (Helianthus annuusL. var. Giganteus) to15NO2, at concentrations between 5.0 and 72.9 ppb resulted in its uptake by the plants during illumination as well as during darkness. The NO2, flux increased linearly with increasing NO2, concentrations in both treatments. Evolution of NO2by sunflowers was not observed. During illumination, measured and potential N Of uptake were equal, which indicates that the uptake of NO2was only limited by stomatal resistance, whereas in darkness, an additional internal resistance to NO. cannot be excluded. After15NO2, exposures, the highest proportions of the15N tracer were fixed as protein nitrogen or as heterocyclic nitrogen compounds and glucosamine. Under both treatments there were remarkably high15N enrichments in the fraction ‘soluble amino acid nitrogen’, indicating a rapid assimilation of the nitrogen derived from15NO2, A linear relation was found between the δ15N values of nitrogen pools investigated and the15NO2concentrations after exposures in light as well as after night‐time fumigation. Apparently, all the enzyme systems involved in the assimilation of the NO2nitrogen must be available in sufficient amounts in plant tissues during exposures. Even after exposures in the dark, about 95% of the absorbed15NO2, nitrogen was fixed in reduced organic nitrogen compounds, which indicates that the assimilation of atmospheric NO2, might not depend on the production of reduction equivalents by photosynthesis. The mechanism of NO, assimilation via nitrate/nitrite reductase within the exposed sunflowers is discussed.
Predictions of where minimal damage to jarrah roots could result in tree death
Authors: DAVISON E. M. , TAY F. C. S. 
Published: April 2006

summaryField observations of Eucalyptus marginata Dorm ex Smith (jarrah) trees on sites infested with Phytophthora cinnamomi Rands showed that sudden and sustained stem shrinkage at 1–3 m preceded crown death. This was interpreted as indicating severe water deficiency in the stem base before the foliage died. Reduced mot conduction might be an important factor leading to tree death. Measurements of conduit length in stems and roots showed that c. 15% were 1 m long and the remainder 40–50 cm long. Qualitative measurements of sap wood conduction were made in 20 cm‐long segments of large horizontal jarrah roots using gas flow at positive pressure. Conduction. expressed as cm3 gas flow mm −2 min−1 increased with increasing distance from the tree bole. This increase was associated with an increase in vessel cross‐sectional area, not with increasing vessel number or a decrease in the proportion of tylosed vessels. Observations on roots from trees from two sites, part of each site being infested with P. cinnamomi, indicated that maximum conduction mm−2 along a root was associated with site, not whether or not the site was infested with P. cinnamomi. Our calculations show that conduction in large horizontal roots is not constant, but decreases dose to the base of a jarrah tree, so that damage close to the bole will have the greatest effect on water movement to the foliage.
Mycorrhizal fungus propagules in the jarrah forest
Authors: BRUNDRETT MARK C. , ABBOTT L. K. 
Published: April 2006

summarySpatial variations in the capacity of propagules of arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi to form associations in their natural habitats were investigated using bioassays with bait plants grown in intact cores of forest soil. These cores were collected from a sclerophyllous forest community dominated by Eucalyptus marginata Donn ex Smith (jarrah) and E. calophylla Lindley (marri) trees with a diverse shrub understorey in the mediterranean (winter rainfall) climatic zone of Western Australia. Small‐scale (adjacent core) variations in the capacity of AM fungi to form associations were found to be as substantial as differences between locations 1 5 m apart. Comparisons of AM fungus colonization patterns within the roots of seedlings growing in the same core indicated that there was considerable spatial heterogeneity in the inoculums potential of ‘individual’ fungi within these 1 1 volumes of soil. A second experiment included bait plants to measure ECM formation as welt as AM formation and also considered the impact of soil disturbance. The disruption of hyphal networks reduced mycorrhizal formation somewhat, but it still remained highly variable. Some of this spatial heterogeneity could be attributed to differences in the organic matter content, length of fungal hyphae, or length of old mycorrhizal roots, measured within soil cores. In jarrah forest soil, mycelial systems of AM and ECM fungi apparently were localized in separate domains, and there were also zones where non‐mycorrhizal roots (mostly cluster roots produced by members of the Proteaceae) predominated. More research is required to determine the size of domains of mycorrhizal mycelial systems in soils, how these spatial patterns change with time, and if they are associated with zones of resource utilization by different ‘functional groups’ of roots.