bluuebunny/crossref_metadata_2025 huggingface dataset:
Holocene history of the forest–alpine tundra ecotone in the Scandes Mountains (central Sweden)
Authors: KULLMAN LEIF
Published: April 2006

summary

The Holocene history of the forest‐alpine tundra ecotone in Central Sweden (Scandes Mountains) is inferred from radiocarbon analyses of subfossil wood remains. Pinus sylvestris was the dominant subalpine tree species during the early Holocene, when it ascended almost 200 m higher than currently. A short climatic episode (less than 100 years) is postulated to have triggered erosional processes around 6300 n.p., and extinguished the upper part of the subalpine pine woodland. Subsequently, a subalpine belt of Betula pubescens ssp. tortuosa and Alnus incana developed. A Holocene thermal optimum occurred around 6100 b.p., when the birch/alder belt nourished and the tree‐limits probably reached their highest levels during the Holocene. Shortly after 6000 b.p., a long‐term pine forest retrogression started and the birch/alder belt was disrupted by expanding snow‐beds. Pine receded slightly at its tree‐limit, but the uppermost belt of closed pine forest (presently dominated by birch) remained intact until c. 3300 b.p., when a severe climatic deterioration occurred. The present‐day subalpine belt of pure birch forest developed successively and increased in vertical extent after c. 5300 b.p., when summer temperature declined. The evolution of the birch belt is postulated to have been ultimately a response to decreased seasonally, which favoured birch at the expense of pine. Because of the ‘inertia’ characterizing the highest pine forest, the birch belt was relatively narrow until a major thermal decline e. 3300 b.p., when it made a massive downslope expansion. The latest phase of pine recession was during the Little Ice Age, 800–300 b.p.
The effects of root treatments on growth of the primary leaves of Phaseolus vulgaris L.: biophysical analysis
Authors: MILLIGAN S. P. , DALE J. E.
Published: April 2006

summary

Plants of Phaseolus vulgaris L. were grown at 22.5 °C and transferred to nutrient solution held at that temperature or at 10 °C; other plants were subjected to a pruning treatment that removed all lateral roots and part of the main root. Both root treatments resulted in a substantial reduction in growth of the primary leaves but did not affect leaf water potential or its components, n and P, except briefly for the root‐cooled plants. Treatments did not increase the wall yield threshold, Y, of leaf tissue which was always lower than in control plants; consequently the effective turgor for growth, P–Y, was greater in treated plants. Both treatments reduced wall extensibility, measured by a modified Instron technique and from the relationship between growth of leaf pieces and their turgor, and it is suggested that this is responsible for the reduction in leaf growth.
Continuity of chloroplast and endoplasmic reticulum membranes in Chara and Equisetum
Authors: McLEAN B. , WHATLEY J. M. , JUNIPER B. E.
Published: April 2006

summary

Continuity between the endoplasmic reticulum and the plastid envelope has often been reported, but has seldom been demonstrated convincingly. Using rapid‐freezing and freeze‐fracturing techniques, we have shown that in the green alga, Chara globularis var. capillacea, and the lower vascular plant, Equisetum telmateia, such continuity is of frequent occurrence. Comparable chemically fixed, resin‐embedded tissues hardly ever reveal connections between the two organelles.
Differences in the spectral characteristics of birch canopies exposed to simulated acid rain
Authors: ASHENDEN T. W. , WILLIAMS J. H.
Published: April 2006

summary

Seedlings of silver birch in a polythene tunnel were exposed to simulated acid rain at pH values of 2.5, 3.5, 4.5 and 5.6 while growing in pots of either John Innes No. 2 potting compost or an Arfon series soil. Measurements of visible and near infrared radiance were taken from the canopies of groups of plants exposed to each of the rainfall treatments, after 34 weeks for plants grown in John Innes compost, and after 75 weeks for plants grown in both soils. Plots of reflectance against wavelength revealed that only plants exposed to the control pH 56 treatment retained the shape of curve that is characteristic of healthy green vegetation. Discriminant analysis showed that the radiometer data could be used to distinguish between birch canopies which had been exposed to the different rainfall treatments after both 34 and 75 weeks.

The potential use of radiometry is discussed for identifying plants growing under the stress of acid rainfall in both controlled environments and in the field. It is apparent that further research using the more sensitive scanners now available will be required in order to improve the accuracy of this survey technique.
Comparative studies of plant growth and distribution in relation to waterlogging
Authors: WALDREN S. , ETHERINGTON J. R. , DAVIES M. S.
Published: April 2006

summary

Populations of Geum rivale L. and G. urbanum L. were collected from a range of habitats; G. rivale usually occurred in wetter and less‐shaded habitats than G. urbanum. Populations differed significantly in a number of respects; most differences between G. rivale populations were related to the sizes of leaves produced and to plant stature, whereas most of the variation in G. urbanum was related to differences in growth rates. The two species responded very differently to waterlogging, but there was only slight intraspecific variation in waterlogging tolerance in either species. Progeny of hybrid individuals were raised as families; their response to waterlogging was similar to that of one or other of the parent species. In G. rivale and other relatively tolerant families waterlogging generally caused a slight increase in shoot: root dry weight ratio, a small decrease in root dry weight, and had little effect on specific leaf area. Waterlogging of G. urbanum and less‐tolerant families caused a large increase in shoot: root ratio, a large decrease in root dry weight, and a decrease in specific leaf area. Tolerant families always had pronounced axillary bud proliferation, usually accompanied by the development of a rhizome‐like caudex. Less‐tolerant families and G. urbanum lacked a caudex, and had reduced axillary bud proliferation. Many of these traits were found to be highly heritable in hybrid families. The ratio of drained: flooded values was used as a measure of response to waterlogging, and showed highly heritable differences between hybrid families for root dry weight, shoot: root ratio and specific leaf area, indicating that these measures of waterlogging tolerance are genetically determined. Families whose maternal parents were morphologically similar to G. rivale were always relatively tolerant of waterlogging, but some families that were similar to G. urbanum were also tolerant. The results emphasize the effect of waterlogging on plant root formation; while there were also important effects of waterlogging on shoot growth and development, the primary effect appeared to be on the root system. These results are discussed in relation to theories of hybrid ecology, and the need for further comparative studies of hybrid ecology is emphasized.
Interaction between the pollen tube and stigmatic cell wall following pollination inBrassica oleracea
Authors: ELLEMAN CAROLE J. , WILLSON CLARE E. , SARKER R. H. , DICKINSON H. G.
Published: April 2006

summary

Electron microscopic observations have revealed the stigmatic papilla wall ofBrassica oleraceaL. to be composed of several distinct layers. Measurement of the thickness of the major components of this wall has demonstrated a significant difference in cuticle thickness between the two S (incompatibility) genotypes under study. It is suggested that cuticle thickness is responsible for differences observed in the rates of pollen hydration on the stigma surface. The relevance of tins finding to the genetical control of pseudocompatibility is discussed. Unusually, the pectocellulosic component of the papillar cell wall is composed of three layers. On pollination, the outer layer detaches to permit the elongating pollen tube to pass down the papilla within the wall itself. At the base of the papilla, the tube becomes truly extracellular, growing down in the intercellular spaces between stylar parenchyma cells. Following a bud pollination, the pollen tube may even penetrate the complete cell wall and grow down the length of the cell, invested on one side by the plasma membrane and on the other by the inner face of the pectocellulosic wall. These tubes experience some difficulty in traversing the cell wall at the base of the papillar prior to entering the intercellular spaces of the style.
Metabolic changes associated with akinete germination in the cyanobacterium Anabaena doliolum
Authors: RAI A. N. , RAO V. V. , SINGH H. N.
Published: April 2006

summary

The energy requirements of akinete germination in A. doliolum were met initially from aerobic oxidation of endogenously stored carbon reserve. The germination of non‐photosynthetic akinetes commenced in light with new protein synthesis followed by the simultaneous development of oxygenic photosynthesis, nitrate reductase activity, glutamine synthetase activity and aspartate dehydrogenase (AsDH) activity by 24 h and heterocyst formation and nitrogenase activity by 60 h. Glutamate‐oxaloacetate transaminase (GOT) and glutamate‐pyruvate transaminase (GPT) activities were present in mature akinetes and only GPT activity increased during akinete germination. The simultaneous appearance during the course of germination of oxygenic photosynthesis, nitrate reductase activity and glutamine synthetase activity much before that of N2 fixation, implies that oxygenic photosynthesis is more closely associated developmentally with carbon dioxide and nitrate assimilation than with N2 assimilation. The activities of the transaminases (GOT and GPT) during the initial stages of germination suggest a significant role for these enzymes in amino‐acid metabolism associated with germination. The appearance of nitrate reductase activity under N2‐fixing conditions, in the absence of nitrate, suggests that the nitrate assimilating enzyme is not nitrate inducible.
The inhibition of ammonium uptake by nitrate in wheat
Authors: DEIGNAN M. T. , LEWIS O. A. M.
Published: April 2006

summary

The improvement of root growth in hydroponically grown crop plants such as wheat when nitrate is added to an ammonium‐only nitrogen source is possibly brought about by a suppression of the over‐rapid absorption of ammonium by nitrate, thus alleviating the stress imposed by root‐based ammonium assimilation on the supply of carbon skeletons required for root growth.

The degree of suppression of ammonium absorption by nitrate in hydroponically grown wheat was investigated by measuring the relative rates of absorption of 15N from nutrient solutions containing 2 mM l6N nitrate, 2 HIM 15N ammonium, 2 mM 14N nitrate + 2 mM 15N ammonium, 2 mM 14N nitrate + 2mM 14N ammonium or 3 mM 14N nitrate + 1 mM 15N ammonium.

After 8 h 15N feeding, 24% more 15N was found in ammonium‐only fed plants than in nitrate‐only fed plants. The l5N content of plants fed equal concentrations of 14N nitrate and l5N ammonium was 44 % lower than that of 15N ammonium‐only fed plants; those fed a 3:1 mixture of 14N nitrate and l5N ammonium had a 15N content 68%, lower than that of 15N ammonium‐only fed plants. The l5N nitrate +14N ammonium fed plants possessed a 15N content 32% below that of 15N nitrate‐only fed plants.

It thus appears that not only is there a measure‐able suppressive effect of ammonium on the uptake of nitrate ions by wheat plants but that the inverse effect is even more pronounced and could account for observed effects of mixed ammonium + nitrate nutrition on root growth.
Influence of light and form of nitrogen on chlorine requirement of kiwifruit
Authors: SMITH G. S. , CLARK C. J. , BUWALDA J. G. , GRAVETT I. M.
Published: April 2006

summary

The extent to which light, potassium, and form of nitrogen (ammonium and nitrate‐nitrogen) modified the requirement by kiwifruit (Actinidia deliciosa var. deliciosa) for chlorine was examined in solution culture. A greater concentration of chloride was required in the nutrient solution for maximum growth under low irradiance than under high irradiance. In the absence of chloride, growth was severely restricted and the response to potassium was significantly reduced, especially under low light.

Greater concentrations of chloride accumulated in the leaves of plants grown under high irradiance than under low irradiance. Increasing the concentration of nitrate in the leaves either by growing the plants under low light or by increasing the quantity of nitrate in the nutrient solution, substantially reduced the accumulation of chloride. The decrease in the concentration ot chloride was accompanied by an increase in the concentration of nitrate. Thus the combined concentration of nitrate and chloride was relatively constant over a wide range of treatments suggesting that a negative feedback mechanism may be operating in this species. However, while nitrate was preferentially accumulated by kiwifruit plants it could not substitute fully for chloride. Once the concentration of chloride in the leaves was decreased below 70μmolg−1 d. wt by competing nitrate ions, growth was substantially reduced. It is concluded that the effect of light on the chloride status of kiwifruit plants can largely be explained in terms of the strong competitive effect from nitrate ions, with greater concentrations of nitrate accumulating in the leaves under low irradiance than under high irradiance.

The negative effect of potassium on the chloride status of the plants is not considered to be a specific physiological effect but rather the consequence of chloride, along with other non‐limiting nutrients, accumulating in the tissues of the severely potassium deficient plants.

The ecological implications of the results are discussed in relation to features of the habitat in China where kiwifruit vines have evolved. The results of the present study are entirely consistent with this species having evolved in an environment where the availability of chloride and ammonium is relatively high while that of nitrate is severely restricted. It is concluded that the high concentration of chloride required in the tissues of kiwifruit vines is an adaptation which minimizes the expenditure of energy on the generation of osmotic pressure in the tissues rather than specifically maintaining charge balance.
Selection of lines with high and low sodium transport from within varieties of an inbreeding species; rice (Oryza sativa L.)
Authors: YEO A. R. , YEO M. E. , FLOWERS T. J.
Published: April 2006

summary

Varieties (including designated cultivars) of Asian rice (a predominantly inbreeding species) show large individual variability in sodium transport and salinity resistance. Recurrent selection has been carried out over five generations with populations of Oryza sativa L. cv. IR36 and cv. IR20. Large numbers of individuals were exposed to a low concentration of NaCl in solution culture, and their sodium uptake determined non‐destructively by sampling the third leaf. The range of sodium concentrations in the leaf was two or three orders of magnitude. Individuals showing both high and low extremes of sodium uptake were selected and allowed to self‐pollinate. The sodium uptake by the progeny was measured in the same way, and the selection repeated. Significant differences in the frequency distribution of sodium transport between the selected lines were evident in both varieties after three cycles of selection. The lines continued to segregate in the fourth and fifth generations by which time the high and low selected lines showed substantial differences in sodium uptake. It is concluded that useful genetic diversity for sodium uptake and hence salt resistance exists within modern rice varieties.
Mycelial uptake, translocation and assimilation of nitrogen from 15N‐labelled ammonium by Pinus sylvestris plants infected with four different ectomycorrhizal fungi
Authors: FINLAY R. D. , EK H. , ODHAM G. , SÖDERSTRÖM B.
Published: April 2006

summary

The uptake and assimilation of 16N‐labelled ammonium was followed in Pinus sylvestris L. plants infected with four different ectomycorrhizal fungi, Rhizopogon roseolus Fr. Suillus bovinus (Fr.) O. Kuntze, Pisolithus tinctorius (Fr.) Fr. and Paxillus involutus (Mich, ex Pers.) Cohen & Couch. Plants were grown in flat perspex observation chambers or in Petri dishes containing non‐sterile peat; in each case the fungal mycelium growing from a host plant was allowed to cross a barrier and to colonize an area of peat from which roots had been excluded. Labelled ammonium was fed to the mycelium, and the shoot, root and mycelial tissues analysed for total and 15N‐labelled free amino acid contents after a feeding period of 72 h. High proportions of 15N‐labelled glutamate/glutamine, aspartate/asparagine, and alanine were found in the fungal mycelia of all species except Pax. involutus where labelled aspartate/asparagine was not found. Lower proportions of labelled serine, threonine, tyrosine, lysine, ornithine and arginine were also found in the mycelium. The degree of 15N enrichment declined throughout the transport pathway but between 5 and 50% of the amino acids were 15N‐labelled in the plant shoots. In total, at least 2–3 % of the nitrogen supplied was assimilated as labelled amino acid during the 3 day feeding period, the largest amounts of labelling occurred in glutamic acid/gultamine and aspartic acid/asparagine.
Vesicular–arbuscular mycorrhizas and the soil‐disturbance‐induced reduction of nutrient absorption in maize
Authors: EVANS D. G. , MILLER M. H.
Published: April 2006

summary

This study was designed to test the hypothesis that disruption of the macrostructure of a previously zero‐tilled soil is capable of reducing vesicular‐arbuscular (VA) mycorrhizal infection to a degree such that phosphorus (P) absorption is reduced. Undisturbed soil cores (within plastic cylinders) were excavated from long‐term, zero‐tilled plots. Soil removed from these plots, which was first subjected to structurally disruptive forces and then packed into identical cylinders, formed the disturbed comparisons. Maize(Zea mays L.), wheat(Triticum aestivum L.), spinach(Spinacea oleracea L.)or rape(Brassia napus L.)were grown in the cores and P and zinc (Zn) absorption patterns monitored.

Soil disturbance significantly reduced P and Zn absorption by maize grown in soil originating from three sites differing in local geography and/or texture. Disturbance also reduced mycorrhizal infection in the three soils.

A significant effect of disturbance upon the VA mycorrhizal infection of both maize and wheat roots (both mycorrhizal) and also upon the P absorption by these species was observed. None was found with respect to spinach and rape comparisons (non‐mycorrhizal).

Injection of benomyl, a potent inhibitor of mycorrhizal fungi, into the soil surface significantly reduced the influence of soil disturbance upon P absorption. No significant differences were found in VA mycorrhizal infection within fungicide‐treated cores.

We accepted our hypothesis based upon the above evidence.
Physical and topological assessment of effects of a vesicular–arbuscular mycorrhizal fungus on root architecture of big bluestem
Authors: HETRICK B. A. DANIELS , LESLIE J. F. , WILSON G. THOMPSON , KITT D. GERSCHEFSKE
Published: April 2006

summary

The influence of a vesicular‐arbuscular (VA) mycorrhizal fungus, phosphorus (P) fertilization, and soil microorganisms on growth and root architecture of big bluestem (Andropogon gerardii Vitroari) was investigated. In pasteurized soil, mycorrhizal inoculation significantly improved plant growth and increased root length and the number and the diameter of the primary, secondary and tertiary roots. These differences between mycorrhizal and non‐mycorrhizal plants diminished with added P. In pasteurized soil amended with non‐sterile soil sievate, differences between mycorrhizal and non‐mycorrhizal plants were still obvious, but in many treatments these plants grew more poorly (had less dry weight, root length, number or diameter) than their counterparts in unamended pasteurized soil. Growth in non‐sterile soil was also suppressed, and mycorrhizal responses were not detected since all of the plants in non‐sterile soil became mycorrhizal whether or not they were inoculated. Two analyses of calculated parameters which describe root‐system architecture were conducted. The first, specific root length (SRL), revealed that mycorrhizal symbiosis dramatically alters root morphology in soils of low fertility. These changes were similar to the changes evoked by added P. The second, path length (Pe) revealed that mycorrhizal fungi (and to some degree other soil microbes) significantly alter root architecture by reducing the relative amount of root branching. Apparently, mycorrhizal plants develop a more elongate, exploratory growth pattern which permits the fungal hyphae to extract nutrients from a larger volume of soil. In contrast roots of non‐mycorrhizal plants maintain a more highly branched pattern of root growth, and the roots themselves play a more critical role in the direct extraction of nutrients from the soil. These differences in root topology were not directly associated with the concentration of exogenous P, but instead appeared to be controlled by the mycorrhizal fungi themselves. Thus, while internal P content of plants mediates the establishment of the mycorrhizal symbiosis, the fungi can alter the root architecture of the plant to a form which best accommodates the symbiosis under the prevailing fertility and rhizosphere conditions in the soil. By altering root‐system architecture in this manner, the mycorrhizal fungi can control, at least to some degree, the dependence of the host on the symbiosis. Thus, the topology of the root system is contingent upon the microflora in the rhizosphere. The topological analysis revealed differences in root architecture not detected by any of the other measures of root morphology. These differences suggest that mycorrhizal fungi affect root architecture and plant growth in ways not directly associated with phosphorus uptake.
Regeneration of bog liverworts
Authors: DUCKETT J. G. , CLYMO R. S.
Published: April 2006

summary

Leafy liverworts of many species regenerate in slabs cut at various depths from peat cores from two widely different sites. Two patterns are recognizable. Species such as Calypogeia fissa (L.) Raddi, Lophocolea spp., Lophozia ventricosa (Dicks.) Dum., Barbilophozia floerkii (Web. & Mohr) Loeske and Riccardia latifrons (Lindb.) Lindb., which lack underground axes, regenerate most abundantly at the surface but not below 9 cm depth. Other species such as Kurzia pauciflora (Dicks.) Grolle, K. sylvatica (Evans) Grolle, Odontoschisma sphagni (Dicks.) Dum., O. denudatum (Mart.) Dum., Cladopodiella fluitans (Nees) Buch, Cephalozia bicuspidata (L.) Dum. and C. connivens (Dicks.) Lindb. which have underground axes, may regenerate poorly at the surface, much better down to 12 cm or so, and arc still found at 24–30 cm depth. These patterns were found in cores from a live Sphagnum‐covered surface and from a much older cut peat surface recently recolonized by liverworts. These results suggest that regeneration is mainly from underground axes rather than from spores or gemmae. The biomass of the underground axes seems to be large. All the axes have fungal associates, and it possible that they are partially saprophytic or parasitic.
The use of benomyl to control infection by vesicular–arbuscular mycorrhizal fungi
Authors: FITTER A. H. , NICHOLS R.
Published: April 2006

The effect of the fungicide, benomyl, on vesicular arbuscular (VA) mycorrhizal infection and phosphorus uptake was studied in two pot experiments, using pea Pisum sativum L., mustard Sinapis alba L. and red clover Trifolium pratense L. Benomyl was either incorporated into the soil or sprayed on to the surface of the pot. Benomyl had no effect on concentrations of water‐soluble P in soil but reduced VA mycorrhizal infection and P inflow in pea. Mustard plants were uninfected even in untreated pots and benomyl had no effect on P inflow in mustard. In clover, there was a positive correlation between shoot P concentration and percentage of root length infected with VA mycorrhizal fungi. Copper, zinc and manganese concentrations in clover shoots were affected by benomyl but this may not have been related to mycorrhizal infection. Benomyl is recommended as a treatment to control VA mycorrhizal infection, with many fewer undesirable consquences than result from soil sterilization.
The isolation of genomic DNA from cyanophage infecting Nostoc and Anabaena species of cyanobacteria
Authors: BANCROFT I. , SMITH R. J.
Published: April 2006

The preparation of genomic DNA from a recently isolated group of cyanophage which infect species of Nostoc and Anabaena (cyanobacteria) has been investigated. Factors which affect the yield of DNA, including culture density on infection, divalent cation requirements, NaCl tolerance and desorption from cell debris, have been assessed. These factors have been incorporated into optimized procedures for the isolation of genomic DNA from five cyanophage. The DNA isolated from the rive cyanophage species was identified using restriction endonuclease fragment patterns.
Photosynthetic characteristics of Spirulina platensis on solid support. Chlorophyll fluorescence kinetics
Authors: SIVAK MIRTA N. , VONSHAK AVIGAD
Published: April 2006

Several aspects of photosynthesis in vivo (CO2 and O2 exchange, chlorophyll fluorescence and its quenching components) were measured in Spirulina platensis after filtering suspensions of this cyanobacteria through fibre glass filters. This simple procedure allowed the use of methods which previously could be applied only to leaves. Fluorescence characteristics displayed by Spirulina in suspension or collected on the solid support were similar, indicating that filtration and assay did not by themselves affect the photosynthetic process. When oxygen evolution and carbon dioxide uptake were followed simultaneously their kinetics differed, and the rate of O2 evolution was often higher than the rate of CO2 uptake. Slow kinetics and other fluorescence characteristics were strongly modified in aged cultures or when nutrient supply during growth was not optimal, or after exposure to photoinhibitory photon flux densities. Photoinhibition and recovery were studied in two strains differing in their sensitivity to high photon flux densities. During illumination using high photon flux densities two phases could be determined. After a few minutes variable fluorescence decreased and ‘dark fluorescence’(Fo) was unchanged, but after prolonged illumination Fo increased. The latter phase appeared earlier in the more sensitive strain and could be brought forward by increasing photon flux densities or, in some circumstances, by increasing [O2].

Results are discussed in terms of the underlying relationships between electron transport and photosynthetic carbon assimilation and of the use of chlorophyll fluorescence as a diagnostic probe. It is suggested that measurement of chlorophyll fluorescence (by itself or in conjunction with quantum yield) on cyanobacteria or algae collected on solid support could provide a convenient screening procedure to assess sensitivity to photoinhibition and to other kinds of stress likely to be encountered in large‐scale culture.
The effect of the gp gene on fruit development in Pisum sativum L.
Authors: PRICE D. N. , SMITH C. M. , HEDLEY C. L.
Published: April 2006

The effect of the yellow‐podded (gp) gene on pea fruits was studied with reference to changes in their plastids. The main effect of the gene was on the mesocarp. The chlorophyll concentration of this layer was depressed to less than 5% of that in normal green pods, allowing considerably higher light transmission through the pod wall. Ultrastructural studies showed that the mesocarp of yellow pods contained plastids with an internal membrane system restricted to single and paired membranes and vesicles. Unlike the chloroplasts of green mesocarps they lacked grana. Large starch grains were found in the plastids of mesocarps from both yellow and green pods.

Well‐developed chloroplasts, lacking starch grains, were found in the thin parenchymatous lining of the endocarp in yellow and green pods. Here chlorophyll concentrations were comparable in the two pod types and considerably higher than those found in the normal green mesocarp. However, the higher light levels transmitted to this layer in yellow pods correlated with a higher chlorophyll a:b ratio compared with that in the green pod.
Studies on the tolerance to SO2 of grass populations in polluted areas
Authors: Taylor H. J. , Bell J. N. B.
Published: April 2006

Grass populations were collected from two sites, Philips Park and Rainham, with different pollution characteristics. They were screened for acute and chronic air pollution injury caused by nitrogen dioxide (NO2) and by sulphur dioxide(SO2) in combination with NO2 in comparison with bred cultivars of the same species grown at a clean air site. No evidence of tolerance of acute NO2 or NO2/SO2, injury was found at Philips Park. A Dactylis glomerata L. population from Rainham showed tolerance to both types of injury. There was also some evidence to suggest that there was a relationship between NO2 and NO2/SO2 tolerance. Chronic NO2 fumigation of Lolium perenne L. was shown to have apparently beneficial effects such as increased growth, increased chlorophyll content and reduced rate of senescence. The Rainham population of this species appears to have a requirement for low concentrations of NO, in the atmosphere. There was an indication that plants which were most tolerant of acute doses of NO2 were those which most benefited from low concentrations of NO2L. perenne and D. glomerata were adversely affected by chronic exposure to a mixture of NO2 and SO2 The Rainham populations of both species were more tolerant of the mixture than bred cultivars. Chronic NO2/SO2 injury was found to be more severe when soil nitrogen was high.
Dynamics of arbuscule development and degeneration in mycorrhizas of Triticum aestivum L. and Avena sativa L. with reference to Zea mays L.
Authors: ALEXANDER TOM , MEIER ROSE , TOTH RONALD , WEBER HANS CHRISTIAN
Published: April 2006

A quantitative light and electron microscope study of developing and degenerating arbuscules of the mycorrhizal fungus Glomus fasciculatum (Thax. sensu Gerd.) Gerd. & Trappe in Triticum aestivum L. (wheat) and Avena sativa L. (oats) was carried out in order to estimate three parameters during the colonization cycle and to compare these parameters to those in Zea mays L. The parameters are: (1) Vv (f,c), the fraction of the host cell volume (c) occupied by a volume of fungus (f); (2) Vv,(cy, c), the fraction of the host cell volume occupied by host cytoplasm (cy); (3) Sv(p,c) the surface area‐to‐volume ratio of the host protoplast (p) to the whole host cell. Uninfected cortical cells of wheat had an Sv,(p,c) of 0.11 μm2μm −3 and those of oats 0.10 μm2μm −3. As the fungus penetrates the cell wall, the protoplast invaginates, causing a decrease in protoplast volume and an increase in St. In wheat this increase reached 1.17 μm2μm−3 and in oats, 1.04 μm2μm−3. When the arbuscule is mature, the fungus occupies 35% of the cell in wheat with 20% as branches and 15% as trunk. In oats, the fungus occupies 36% of the cell, with 23 % as branches and 13 % as trunk. In wheat, host cell cytoplasm was initially 39 % and increased to 21.6% and in oats, from 3.6 to 28.8%. These values are similar to those observed in Zea mays. The rates at which the parameters Vv(f,c) and Sv(p,c) changed during arbuscule development and degeneration were similar. The amount of encasement and host cell cytoplasm showed the greatest variation among host species.
Photosynthesis in discrete regions of leek leaves infected with the rust, Puccinia allii Rud.
Authors: Roberts A. M. , Walters D. R.
Published: April 2006

Photosynthesis was examined in discrete regions of leek (Allium porrum L.) leaves infected with the rust, Puccinia allii Rud. Oxygen evolution, expressed on both a chlorophyll and a leaf area basis, was significantly reduced in pustule regions, coupled with an increase in rates of dark respiration, for the duration of the experiment. The activity of ribulose bisphosphate carboxylase (RuBPcase) was reduced in pustule areas and losses in total soluble protein and chlorophyll were observed. Areas between pustules exhibited photosynthetic rates (on a chlorophyll basis) near to control values and dark respiration was reduced for at least part of the experiment. No significant alteration in RuBPcase activity, total soluble protein or chlorophyll concentrations was detected in interpustule regions. The physiological mechanisms underlying the changes in photosynthesis and respiration within discrete regions of rusted leeks are discussed.
Effects of the fairy ring fungus Agaricus arvensis on nutrient availability in grassland
Authors: Edwards P. J.
Published: April 2006

Agaricus arvensis Schaeff. ex Fr. produced a pattern (a fairy ring) in the vegetation consisting of three concentric zones of scorched or reddened foliage alternating with zones of more vigorous growth. The outermost zone contained active mycelium; the inner zones were thought to represent the positions of the mycelium in previous years.

Soil samples were taken from the various zones of affected vegetation, and from outside and inside the rings. Concentrations of total nitrogen, phosphorus (total and acetic acid extractable), potassium and magnesium were highest in the active zone; concentrations of these nutrients inside the zones were lower than those outside.

Leaf blades of Agrostis capillaris L. in all zones of affected vegetation had enhanced concentrations of nitrogen. Phosphorus and potassium concentrations in leaves were reduced within the fairy rings, especially in the zones of reddened foliage. It is concluded that the growth habit of the fungus allows it to accumulate nutrients very effectively and may cause nutrient deficiencies in higher plants.

The investment of potassium in sporophores was equivalent to 23 % of that in the soil volume exploited by the mycelium in 1 year. For phosphorus the corresponding percentages were 1–3 of total soil phosphorus and 63 % of acetic acid‐extractable phosphorus. However for nitrogen, calcium and magnesium the quantity in the sporophores was & 1 % of that in the soil.
Phragmites australis: a critical appraisal of the ventilating pressure concept and an analysis of resistance to pressurized gas flow and gaseous diffusion in horizontal rhizomes.
Authors: ARMSTRONG J. , ARMSTRONG W. , BECKETT P. M.
Published: April 2006

The concept of plant ‘ventilating pressures’ is considered by comparing the pressures required to cause various rates of gas‐How through rhizomes of Phragmites australis venting either beneath water or into air. The resistances to pressurized flow in nodal and internodal regions are quantified, and the pressure: flow data analysed mathematically to deduce effective pore‐space diameter in the nodal diaphragms, and the diffusive resistances of the diaphragms and intemodes.

The value traditionally termed ‘ventilating‐pressure’, the minimum pressure required to cause a venting of gas into water, is shown to be a function of surface tension effects at the venting surfaces and not a measure of gas‐flow resistance within the plant.

With venting to air rather than water, gas flows occurred at all applied pressures greater than atmospheric and pressure‐flow resistance within the plant was determined from the gas flow: pressure relationship. Pressure‐flow resistance was much greater in the nodal pith diaphragms (6–210 MPa s m−3) than in internodal pith cavities (0.001 5.040 MPa s m−3; path length, 100 mm) and was chiefly a function of pore‐size, pore numbers and path length within the small stellate parenchyma layers of the diaphragms. The domed nature of diaphragms reduces resistance by increasing the pore numbers. The effective pore diameters within the small stellate parenchyma of the diaphragms were estimated from the pressure: flow data using a modification of the Poiseulle equation. The values obtained ranged from c. 3.7 μm, and corresponded closely with diameters found previously by scanning electron microscopy.

It is concluded that both large and small stellate parenchyma must contribute significantly to the diffusive resistance of tile diaphragms in accordance with path lengths and porosity; and that, in contrast with pressure‐flow resistance, the internodes because of their length, should have the greater impedance. Estimated values for the pith diaphragm diffusive resistance were 1–13 Ms m−3 (path length, 1.7–3 mm), whilst pith cavity resistances, (path length 100 mm), were 25–1100 Ms m−3. In the latter, the variation was attributable chiefly to the widely varying rhizome diameters: porosities of wide rhizomes were greater than those of narrower ones because of large pith cavities. The fractional porosity due to cortical aerenchyma channels (10–20%) was not related to rhizome thickness.

It is concluded that gas‐flow resistances in Phragmites are sufficiently small to allow for substantial long‐distance transport by convection or diffusion.
The response of stomata to ring‐substituted indolylacetic acids
Authors: THOMSON A. , COX R. C. , MANSFIELD T. A.
Published: April 2006

summary

Indol‐3‐ylacetic acids with substituents in the aromatic ring have been synthesised and their effect on stomata on isolated epidermis tested. Unlike indol‐3‐ylacetic acid which induces stomatal opening, all the substituted acids caused closure. The perception mechanism in the guard cells may therefore involve receptors with high specificity for IAA. The ability of guard cells to discriminate IAA from closely related molecules may be higher than in other cellular systems.
Urban distribution of Rhytisma acerinum (Pers.) Fries (tar spot) on sycamore
Authors: LEITH I. D. , FOWLER D.
Published: April 2006

This study examined ecological aspects of the distribution of tar spot disease caused by the fungus Rhytisma acerinum (Pers.) Fries on Acer pseudoplatanus L. (sycamore). The host is abundant in Edinburgh and surrounding areas yet no tar spots were found in the city, although they were abundant on sycamore in the surrounding countryside, especially at sheltered sites. The vertical distribution from a localized source of leaf litter from infected sycamore showed an approximately linear relationship between tar spot index of attached leaves (TSI = no. of tar spots per 100 cm2 of leaf) and the log of height of such infected foliage above the ground. The distribution of tar spots was controlled primarily by the presence or absence of overwintered sycamore leaves infected with R. acerinum. In Edinburgh these leaves are actively removed by man and passively by wind, so reducing the potential source of inoculum by the following spring.

The presence of SO2 was unimportant in the distribution of R. acerinum. An experiment to study the relative importance of current air concentrations of SO2 on the incidence of infection by R. acerinum showed that the average SO2 concentration of < 50 μg m‐3 hail no effect. The observed distribution of tar spot throughout the city and surrounding countryside could be explained entirely by distance from the nearest source of inoculum without involving a role for air pollutants.
Effects of microwave treatment of soil on growth of birch (Betula pendula) seedlings and infection of them by ectomycorrhizal fungi
Authors: GIBSON FIONA , FOX FRANCES M. , DEACON J. W.
Published: April 2006

Seedlings of birch (Betula pendula Roth.) were grown for 12 weeks in small volumes of field soils heated in a microwave (MW) oven for different times and then either supplemented or not with inocula of ectomycorrhizal fungi and, in one case, with fresh agricultural soil. Growth of roots and shoots was assessed, and the incidence of different mycorrhizal types, distinguished by colour and morphology, was recorded. Bacterial and fungal populations were determined by dilution plating after MW treatment of soils.

In four soils, shoot and root growth were markedly enhanced by MW treatments that raised the soil temperature to 60°C or more, irrespective of the exposure times (20–50 s) needed for this. Shoot dry weights were increased 1·9‐ to 2·9‐fold by MW treatment of two soils from young (11–16 years) birch stands, compared with 8·0‐ and 11·4‐fold for two soils from old birchwoods. But MW treatment of a colliery spoil reduced shoot growth 5‐fold. The growth responses were not related to the size of seedlings in untreated soils. The responses coincided with substantial reductions in the total populations of bacteria and fungi.

Hebeloma subsaponaceum Karsten developed similar numbers of mycorrhizas from mycelial inoculum added to untreated and MW treated soil. But Lactarius pubescent (Fr. ex Krombh.) Fr. developed significantly more mycorrhizas from inoculum added to MW‐treated soil than to untreated soil. This difference between the fungi accords with their classification as, respectively, early stage and late stage in reported mycorrhizal successions on birch.

Some mycorrhizal types developed on seedlings from resident inoculum in soil. Their incidence was reduced by different amounts following MW treatment, suggesting differences in heat‐tolerance of their propagules. Hebeloma sacchariolens Quel., which forms sclerotium‐like bodies and which probably developed from resident inoculum, was unaffected by MW treatment of soil. Some mycorrhizal fungi, notably Thelephora terrestris (Ehrh.) Fr., developed in place of others in soils treated for long times (80–180 s), and they probably developed from airborne spores.
Early events of vesicular–arbuscular mycorrhiza formation on Ri T‐DNA transformed roots
Authors: BÉCARD G. , FORTIN J. A.
Published: April 2006

An in vitro system using Ri T‐DXA transformed roots and the vesicular–arbuscular mycorrhizal fungus Gigaspora margarita Becker & Hall has been developed to study the initial events of mycorrhiza formation. Sucrose, sodium and phosphorus were found to be critical components of the medium used to establish the dual culture. Using a single spore as inoculum it was consistently possible to obtain colonization of a preselected point on the root and to time the colonization process (within 5 days). Abundant viable and aseptic spores can be obtained. The system is especially appropriate for studying the triggering of the fungal biotrophy towards the root.
Time sequence of the infection process eucalypt ectomycorrhizas
Authors: HORAN D. P. , CHILVERS G. A. , LAPEYRIE F. F.
Published: April 2006

The paper‐sandwich technique for simultaneous inoculation of populations of root apices, was used to produce numbers of synchronously developing ectomycorrhizas, and to permit direct time‐sequencing of stages in the infection process in eucalypts. After one day there was evidence of chemical interaction between fungus and host. By two days, sheath formation had started in the cap region, cap cells were invaded by fungus, and apical root tissues commenced to swell. By four days all the anatomical features of an ectomycorrhiza were present, including the Hartig net. Thereafter, mycorrhizal features were merely enhanced and perpetuated by subsequent acrogenous development of the fungus‐root dual organ. The process of mycorrhizal perpetuation involved the same sequence of events (sheath development at the apex associated with invasion of cap cells, modification of other root tissues, then finally formation of Hartig net) as did the initial infection process.
Root hydraulic conductivity of vesicular–arbuscular mycorrhizal green ash seedlings
Authors: ANDERSEN C. P. , MARKHART A. H. , DIXON R. K. , SUCOFF E. I.
Published: April 2006

Green ash (Fraxinus pennsylvanica Marsh.) was either inoculated or not with Glomus etunicatum Becker and Gerd. and grown for 37 d to permit root colonization. Root hydraulic conductivity (Lpp) per unit length was measured on excised root systems to examine the influence of vesicular arbuscular (VA) mycorrhiza inoculation, seedling size, phosphorus (P) nutrition, and biomass distribution. Fertilization with P eliminated significant differences in seedling size and dry matter distribution between mycorrhizal (M) and non‐mycorrhizal (NM) seedlings, but VA mycorrhizas increased root and leaf P concentration. Root Lp was similar in M and NM seedlings of similar size, and was lower in M seedlings for a given root P concentration. Root Lp decreased with age and weight, and increased as the proportion of dry weight in the leaves increased in both M and NM seedlings. Mycorrhizal colonization had no significant effect on root Lp in the absence of a significant growth response.
Relationship of soil fertility to suppression of the growth response of mycorrhizal big bluestem in non‐sterile soil
Authors: KITT D. GERSCHEFSKE , HETRICK B. A. DANIELS , WILSON G. W. T.
Published: April 2006

When growth of vesicular‐arbuscular (VA) mycorrhizal and non‐mycorrhizal big bluestem was evaluated in 15 soils, three different growth response groups were evident. Group one, which included the prairie soils, displayed high mycorrhizal dependency as well as significant suppression of plant growth in non‐sterile soil. Group two showed no mycorrhizal dependency; however, plant growth was suppressed in nonsterile soil. The last group exhibited no mycorrhizal dependency or suppression in non‐sterile soil. Mycorrhizal dependency of big bluestem was not highly correlated with any individual soil parameter; however, concentrations of soil K, Ca, Cu, and Fe were used to successfully classify‘high’or‘low’mycorrhizal dependency. Suppression of plant growth in non‐sterile soil was also related to soil fertility. The magnitude of non‐sterile soil suppression was described by equations using soil Na, Zn, Mn, organic matter, Mg, and NH4. The mechanism of this suppression is still unclear; however, the nutrients which predict suppression may be related to the development of mycorrhizal symbosis or in demand by plants and other microbes, while those nutrients which predict mycorrhizal dependency may be related to those supplied to the plant by the symbiosis.
Salt tolerance in natural populations ofTrifolium repensL.
Authors: AB‐SHUKOR N. A. , KAY Q. O. N. , STEVENS D. P. , SKIBINSKI D. O. F.
Published: April 2006

The salt tolerances of plants from natural populations ofTrifolium repensL. (White Clover) growing in saline and non‐saline sites were compared by root growth tests at a range of NaCl concentrations. Plants from three salt‐marsh sites showed high or very high salt tolerance, with relatively vigorous root growth in 150–200 mM NaCl. Plants with two non‐saline inland sites showed little or no tolerance. A sea‐cliff population and plants of cv. Gwenda showed intermediate levels of tolerance at low salt concentrations. Halophytic maritime populations may‐provide material for the development of salt tolerant cultivars ofT. repens, a crop plant in which most existing cultivars are thought to be salt‐sensitive.