bluuebunny/crossref_metadata_2025 huggingface dataset:
The responses of four Irish wetland tree species to raised soil water levels
Authors: IREMONGER S. F. , KELLY D. L.
Published: April 2006

The four most common tree species in Irish wetland woods are Alnus glutinosa (L.) Gaertn. (common alder), Betula pubescens Ehrh. (downy birch), Fraxinus excelsior L. (ash) and Salix cinerea ssp. oleifolia Macreight (Salix atrocinerea Brot., common sally). Seedlings of these species were subjected to different soil water levels (half saturated and surface saturated) in their second and third years of growth, and performance was compared to that in a free draining control treatment. All plants survived in the water treatments, except for over 50%, of the B. pubescens. Soil redox potentials indicated a gradient in the degree of hypoxia which seemed to reflect the order of tolerance of the species, as shown by measurements of relative growth and final dry weight. The observed differences in soil redox potentials may have been due to the oxidizing activity of the roots of tolerant species, which showed varying degrees of stem base hypertrophy and associated proliferation of lenticels. Species were affected by the waterlogging treatments in the order B. pubescens (most adversely affected) > A. glutinosa > F. excelsior > S. cinerea ssp. oleifolia.
The germination characteristics of seeds from Lychnis viscaria L. (Viscaria vulgaris Bernh.), Potentilla rupestris L. and Veronica spicata L.
Authors: WHITTINGTON W. J. , WILSON G. B. , HUMPHRIES R. N.
Published: April 2006

The effects of temperature, date of sowing and the presence or absence of light on the percentage germination by seeds of Lychnis viscaria L. (Viscaria vulgaris Bernh.), Potentilla rupestris L. and Veronica spicata L. were studied. It was found that both in controlled environments and in the open, the order of time‐to‐germination was the same, namely L. viscaria, V. spicata and finally, P. rupestris. The latter species required a temperature in excess of 10°C to germinate and V. spicata required light to germinate. A small (< 5%) number of V. spicata seeds did, on occasion, germinate in the dark and the seeds of this species whether fully imbibed or not, required a shorter period in the light than P. rupestris. Because the seeds used were stored and germinated under artificial conditions these findings can only serve as a first, but important, stage in understanding how the seeds germinate in nature.
Stomatal closure fully accounts for the inhibition of photosynthesis by abscisic acid
Authors: DOWNTON W. J. S. , LOVEYS B. R. , GRANT W. J. R.
Published: April 2006

The partial pressure of intercellular CO2 calculated from gas exchange data for abscisic acid‐treated leaves of grapevine (Vitis vinifera L.) and sunflower (Helianthus annuus L.) does not indicate the average intercellular CO2 of the leaf. The latter can be determined from chlorophyll fluorescence quenching information and accurately modelled from gas exchange data. Stomatal closure can fully account for previously assumed non‐stomatal inhibition of photosynthesis. Autoradiograms show that abscisic acid induces non‐uniform gas exchange over small areas of the leaf.
Ultrastructure of chloroplast membranes in leaves of maize and ryegrass as revealed by selective staining methods
Authors: LAWTON JUNE R.
Published: April 2006

Leaves of Lolium multiflorum Lam. and Zen mays L. of different ages were prepared for TEM by a number of cytochemical methods. After post‐fixation in potassium ferricyanide with osmium tetroxide the peripheral reticulum in both mesophyll and bundle sheath chloroplasts of maize stain very clearly. Post‐fixation with uranyl acetate, copper and lead salts also stains the chloroplast envelope rather than the internal thylakoid system. Differences between the mesophyll and bundle sheath chloroplasts of maize and between those of ryegrass are revealed after post‐fixation in zinc iodide with osmium tetroxide. After post‐fixation in potassium iodide with osmium tetroxide the loculi stain less intensely than in zinc iodide. Malachite green added to glutaraldehyde at pH 70 enhances membrane staining in general and reveals large lipid drops in the stroma. At pH below 6–0 only the ‘A’ space is stained. The ‘A’ space and the loculus are stained when ethidium bromide is added to glutaraldehyde. The different reactions of the chloroplast membranes probably reflect differences in chemical composition.
Effect of inorganic phosphate, 3‐phosphoglycerate and glucose‐6‐phosphate on net starch synthesis by isolated chloroplasts of Codium fragile (Suringar) Hariot
Authors: WILLIAMS MICHAEL L. , COBB A. H.
Published: April 2006

Net starch synthesis isolated chloroplasts of Codium fragile appears to be regulated in a similar manner to that of vascular plants. Exogenous 10 mol m−3 PGA stimulated net starch synthesis at 200 μmol m−2 s −1 (PPFD) by approx. 69%, whilst 10 mol m−3 P1 not only inhibited synthesis but also promoted net starch degradation. However, unlike vascular plant chloroplasts, 10 mol m−3 G6P was found to stimulate net starch synthesis by approx. 52% under the same conditions. This apparent difference in response to exogenous G6P is discussed in relation to the operation of the P1‐G6P translocator in chloroplasts of this species
Growth and nutrition of guayule (Parthenium argentatum) in a saline soil as influenced by vesicular–arbuscular mycorrhiza and phosphorus fertilization*
Authors: PFETFFER C. M. , BLOSS H. E.
Published: April 2006

Growth of guayule (Parthenium argentatum A. Gray) in a moderate and a highly saline‐sodie soil was increased by inoculation with Glomus intraradices Schenck & Smith. The growth of guayule plants was stimulated equally by the addition to the soil of either 100 μg g1 of phosphorus (P) or inoculum of G. intraradices.

Mycorrhizal plants had increased concentrations of PO4 and decreased concentrations of Na in shoot tissues compared to non inoculated control plants. Addition of 100/μgg 1 of P to the soil increased the accumulation of PO4 in the shoot tissues and in most instances decrease accumulation of Cu, Zn, Na, K, and SO4. Concentrations of Na, K, and Cl and frequently Mn in the shoot tissues were increased while the concentrations of PO4 and SO4 in shoot tissues were generally decreased by the addition of NaCl to the soil.

Addition of 100μgg 1 of P to the soil did not markedly affect the colonization of guayule roots by G. intraradices. The roots of mycorrhizal guayule grown in soil with NaCl added contained decreased numbers of arbuscules and vesicles. Addition of both P and NaCl to the soil reduced the formation of arbuscules and vesicles and reduced the occurrence of moderate and heavy levels of root colonization.
A new method for obtaining Anabaena‐free Azolla
Authors: LIN CHANG , WATANABE I.
Published: April 2006

Anabaena azollae can be completely eliminated from megasporocarps of Azolla by the removal of the indusium and apical membrane after horizontally cutting the megaspore apparatus beneath the apical membrane. All subsequent sporelings of Azolla are free from Anabaena. These do not fix N and fail to survive on N2‐free media. They grow normally, however, in N2‐containing liquid medium or in a soil‐water system with small amounts of added N and eventually bear sporocarps. Anabaena is again absent in the new megasporocarps and sporelings of Azolla derived from the second generation of megaspores are likewise Anabaena‐free.
Mass allocation, moisture content, and dispersal capacity of wind‐dispersed tropical diaspores
Authors: AUGSPURGER C. K.
Published: April 2006

Among 34 wind‐dispersed tree species on Barro Colorado Island, Panama, the wet mass of diaspores ranges over six orders of magnitude, The seed mass as a percentage of diaspore mass (S/D) varies greatly among species from 14 to 94% with a mean value of 61% The mean percent moisture of diaspores is 10% no consistent differences occur between seed and non‐seed components of diaspores in percent moisture. Wing‐loading (weight/area) and hence dispersal capacity varies over one order of magnitude among these species and is correlated more highly with S/D than with percent moisture of diaspores. Compared to fruit diaspores, seed diaspores have less mass and a greater S/D, and are slightly more dehydrated. As a result, seed diaspores have lower wing‐loading and greater dispersal capacity than fruit diaspores. The morphological/aerodynamic features of a diaspore also have a significant effect on the mass variables. Overall, the type of diaspore (fruit or seed) is of major importance in explaining mass differences of diaspores among these wind‐dispersed species; morphological features and dehydration ability contribute secondarily.
Phragmites australis– A preliminary study of soil‐oxidizing sites and internal gas transport pathways
Authors: ARMSTRONG J. , ARMSTRONG W.
Published: April 2006

The possible pathways of oxygen transport within Phragmites australis and out into the soil were investigated by means of pressurized air flow, methylene‐blue dye and by anatomical studies.

In most cases, gas was easily forced through the plants, thus demonstrating gas‐space connexion between aerial shoot, rhizomes and roots and a relatively low resistance to flow. Gas‐space connexions between the pith cavity and cortical aerenchyma in the rhizomes were also detected and were investigated anatomically they are present only in nodal regions just above the insertion of the pith diaphragm and take the form of radial channels through the stelar cylinder. Similar pathways in the culm connect the pith cavity with nodal lines of stomata and it is suggested that these regions may often form the major oxygen entry point to the rhizome‐root system.

A failure to effect pressurized gas‐flow through some rhizomes led to the detection of secondary barriers to longitudinal gas‐flow. Seemingly a response to wounding, these are an impenetrable barrier to gases, to flooding, and probably also to microorganisms, and take the form of tylosoidal growths from and within regions of stellate‐and/or circumvascular‐parenchymas such as those of the nodal diaphragms. Stellate parenchymas of various sorts were found to be a common feature of the gas‐path in Phragmites and evidently they form an important component of the gas‐space system occurring within the nodal radial channels, the nodal diaghragms and, rather unusually, the root‐shoot junctions where they must confer a porosity which is higher than for most plants.

As measured by methylene‐blue oxidation, oxygen release from underground parts was most rapid from young adventitious and secondary roots and particularly basal tufts of fine laterals. Zones of oxidation also occurred around the sprouting tips of horizontal and vertical rhizomes. Dormant tips showed very little oxidizing power, whilst the rhizomes themselves and the older parts of adventitious roots showed none. This was associated with cuticularization of the rhizome and hypodermal suberization and lignification; oxygen‐impermeable regions of the roots were also hyperdermally suberized and lignified.

The findings are discussed in relation to the use of Phragmites in sewage‐treatment beds.
Comparative effects of the soil microflora on ectomycorrhizal inoculation of conifer seedlings
Authors: Mcafee B. J. , Fortin J. A.
Published: April 2006

The effects of vegetative inoculum of Laccaria bicolor (Maire) Orton, Pisolithus tinctorius (Pers.) Coker & Couch and Hebeloma cylindrosporum (Bull. & St. Am.) Quél. and addition of fine soil suspensions to jack pine (Pinus banksiana Lamb) and American larch [Larix larcina (DuRoi) K. Koch] seedlings were studied under controlled environmental conditions. Mixed inocula, composed of either (1) equal proportions of the above three mycobionts or (2) equal proportions of Laccaria and Hebeloma were also tested.

Larch seedlings inoculated with L. bicolor formed significantly more mycorrhizas than did any of the other inoculum treatments. Untreated pine seedlings showed similar mycorrhiza development with L. bicolor and the two mixed inocula. On pine seedlings that received a fine soil suspension L. bicolor formed significantly more mycorrhizas than did other inocula.

The addition of fine soil suspensions, containing biological propagules less than 45 μm, enhanced mycorrhiza formation and influenced shoot length and dry weight with some of the tested inocula, depending on the tree species. The competitive ability of the mycobionts in mixed inoculum was also affected by the soil suspensions.

That P. tinctorius was not competitive in the mixed inoculum was attributed to its slower growth rate under the experimental conditions.
Nickel toxicity in mycorrhizal birch seedlings infected with Lactarius rufus or Scleroderma flavidum I. Effects on growth, photosynthesis, respiration and transpiration
Authors: JONES MELANIE D. , HUTCHINSON THOMAS C.
Published: April 2006

Growth, photosynthesis, transpiration and respiration were measured in birch (Betula papyrifera Marsh.) seedlings exposed to 85mUM nickel. The seedlings were inoculated with either Scleroderma flavidum E. & E., a fungus known from previous work to increase Ni tolerance, or Lactarius rufus (Scop, ex Fr.) Fr., another mycorrhizal associate, but one which did not increase Ni tolerance, or else they were not inoculated. Decreased water uptake per seedling was used as an indicator of the progression of Ni toxicity in the seedlings over 16 weeks. These measurements indicated that L. rufus provided some initial protection against Ni toxicity. However, water uptake in S. flavidum‐infected seedlings was least affected by Ni, and was significantly higher than that in L. rufus infected and uninoculated seedlings after week 10. Total dry weights of the S. flavidum‐infected seedlings were higher than those of other seedlings at weeks 12 and 21. Chitin analysis was used to determine the fungal component of root weight. The weight of S. flavidum tissue per root was significantly greater than that of L. rufus in both the Ni‐treated and control (non‐Ni‐treated) seedlings, and this amount increased with time. Lactarius rufus did not grow once the roots were exposed to Ni. Thus, the ability of S. flavidum to continue to grow following Ni exposure may be an important characteristic distinguishing between fungi which are ‘effective’ or ‘ineffective’ in enhancing metal tolerance. Nickel reduced photosynthetic rates in seedlings infected with S. flavidum relative to S. flavidum‐infected seedlings not treated with Ni, but did not have this effect in uninoculated seedlings. Respiration rates were not affected by metal treatment, or by mycorrhizal formation. Thus, S. flavidum increased Ni tolerance in the host, but not by preventing Ni‐induced reductions in photosynthetic rates or by affecting shoot respiration rates.
Growth responses and delayed winter hardening in Sitka spruce following summer exposure to ozone
Authors: LUCAS P. W. , COTTAM D. A. , SHEPPARD L. J. , FRANCIS B. J.
Published: April 2006

Two‐year‐old seedlings of Sitka spruce [Picea sitchensis(Bong) Cart.] were exposed to < 5, 70, 120 and 170 nl l−1O3for 7 h day−1in large ventilated glasshouses during the summer of 1986. Relative growth rates (RGR) were calculated at intervals throughout the summer and autumn using a non‐destructive technique in which measurements of stem height and diameter were used to estimate above‐ground biomass. No statistically significant effects of the ozone on growth were apparent during or after the period of fumigation, and growth of the seedlings had largely been completed by the end of August. The winter hardiness of these plants was subsequently tested on 10 November and 8 December by subjecting detached shoots to a range of carefully regulated freezing temperatures in controlled environment chambers. The results for the samples taken on the earlier date suggested that plants exposed to ozone were more sensitive to frost than the controls, and that this effect was dependent on the concentration of the pollutant. In the samples taken later, all the shoots appeared to have hardened equally to freezing temperatures in excess of about –20 °C. The results suggest that early autumn frosts might be damaging to Sitka spruce after exposure to high ozone concentrations in summer.
C4 plants as valuable model experimental systems for the study of photosynthesis
Authors: FURBANK ROBERT T. , FOYER CHRISTINE H.
Published: April 2006

Two decades have passed since the C4 cycle was first described. In this time, an increasingly large body of information has shown that the complexities of structure and metabolism associated with C4 photosynthesis may be successfully exploited to understand further the molecular biology, biochemistry and structure‐function relationships of photosynthetic cells.
The polyol pattern of fungi as influenced by the carbohydrate nutrient source
Authors: PFYFFER GABY E. , RAST DORA M.
Published: April 2006

Penicillium (P.) italieum (1), Endothia parasitica (2), Agaricus bispours (3), Candida albicans (4), Mucor rouxii (5), Phycomyces (ph.) blakesleeanus (6) and Zygorhynchus moelleri (7) were cultivated in liquid media differing in the carbohydrate source and their free polyol (alditol) composition was established by gas‐liquid chromatography. Total polyol on a dry weight basis ranged from 4‐19% in (1)‐(4), and from 0·2‐2% in (5)‐(7). Species (l)‐(3) contained mannitol, in addition to erythritol, arabitol, and glycerol; the last two were also present in (4)‐(7), together with ribitol. Although the relative proportion of the constituents of the polyol fraction depended on the nutrient Sugar, the pattern of polyols generally remained constant. Notably, the mannitol precursor, fructose, did not induce synthesis of the hexitol in (4)‐(7) nor ribose that of ribitol in (1)‐(3).
Responses of lichens to salinity: concentration and time‐course relationships and variability among Californian species
Authors: NASH T. H. , LANGE O. L.
Published: April 2006

Sensitivity to salinity varied widely among 12 Californian lichen species occurring along a coastal to inland gradient, with the degree of sensitivity being approximately proportional to the distance from the coast where the species grew. For four of those species, it was found that net photosynthesis in three decreased with increasing sea‐salt concentrations, but in Dendrographa minor Darb. it was essentially unaffected. Time‐course studies with Pseudacyphellaria anomala Magn., a sensitivity species, demonstrated that a major decline in net photosynthesis occurred within an hour after submersion in a full strength sea‐salt solution and that the effect was partially reversible, but only up to 12 h after initiation of the treatment. For three sensitive species, an osmotic effect provided by treatment with sorbitol only partially explained the observed changes in gas exchange. Solutions of NaCl of equal osmotic value to full‐strength sea‐salt solutions decreased net photosynthesis more than full‐strength sea‐salt solutions alone. Because NaCl provides the principal ions in sea‐salt solutions, it is inferred that the observed ionic effects were principally due to these ions. Of the sensitive species Evernia prunastri (L.) Ach. was least sensitive to osmotic effects alone, but it was extremly sensitive to salinity.
Maintenance of morphological variation in a biotically patchy environment
Authors: EVANS R. C. , TURKINGTON R.
Published: April 2006

The relationship between morphological variability and biotic environmental heterogeneity was studied in a pasture population of Trifolium repens L. It had been argued that the unexpectedly high levels of variation in T. repens could be maintained by diversifying selection. The mosaic of neighbours (perennial grasses) with which T. repens co‐exists constitutes a prominent element of biotic patchiness that may lead to sorting among T. repens genotypes on the basis of neighbour‐specific compatibilities.

A variation study was conducted on a set of 400 individuals of T. repens collected on a neighbour‐specific basis from a 43–year‐old pasture and grown for over 2 years under common garden conditions. Variation in a set of 12 morphological characters was assessed after 4 months and again after 27 months. After 4 months′ growth, a significant proportion of this variation was accounted for by the neighbour with which the individuals of T. repens had been growing in the pasture. The actual amount of variation accounted for, however, was low (6‐19%).

When the same characters were assessed after 27 months, none of the neighbour‐specific differences in morphology were retained. It is concluded that the original results reflected developmental differences carried over from the pasture, and that diversifying selection is not of importance in the maintenance of morphological variation in this population.
Vegetational history of Carbury Bog (Co. Kildare, Ireland) during the last 850 years and a test of the temperature indicator value of 2H/1H measurements of peat samples in relation to historical sources and meteorological data
Authors: van GEEL B. , MIDDELDORP A. A.
Published: April 2006

A palynological study of contiguous samples of the upper 128 cm of Carbury Bog, Co. Kildare, Ireland, showed details of the fluctuating human impact on the vegetation during the last c. 850 years. During the period of c. 1130–1440 A.D. the landscape around Carbury Bog was still dominated by forest. During the second half of the 15th century there was a considerable reduction of the forested area, reflected in the pollen diagram. The commercial exploitation of the forest during the 17th century resulted in almost complete deforestation. The pollen records for the 18th century vegetation show a rise in the curves of Pinus, Fraxinus and Fagus as a consequence of planting of these trees.

Apart from pollen many other palynomorphs (‘Types’, a.o. fungal spores and rhizopods) were recorded. The spectrum of Types appeared to be comparable with the Type spectrum of continental raised bogs. The results of the macrofossil analysis in combination with the indicator values of some Types were used in a detailed reconstruction of the local vegetation succession and the changes in hydrological and trophic conditions. The disappearance of Sphagnum imbricatum during the late medieval period possibly was caused by the increased influx of dust, as a consequence of man's impact on the environment around the bog. The recent importance of S. magellanicum as a peat forming species is possibly the effect of an increased atmospheric deposition of nitrate.

Parallel to the analysis of micro‐ and macrofossils a sample series from the same monolith was analysed for the ratio of the stable isotopes 2H and 1H. Theoretically the 2H/1H ratio in cellulose of peat‐forming plants should be indicative for palaeotemperatures, but, apart from a temperature dependent signal, this ratio is also strongly related to specific characteristics in the isotopic behaviour of different peat forming species. The overall fractionation is a complex function of climatic and plant‐physiological parameters.

In the present study the results of the 2H/1H measurements were compared with Lamb's palaeoclimatic data derived from historical sources and meteorology. The 2H/1H ratios of Carbury Bog appeared to be negatively correlated with the medieval climatic optimum, the Little Ice Age and the subsequent phase of warming climate. There is an obvious relationship between the 2H/1H ratio and the local succession of peat forming taxa and, as a consequence, with strictly local hydrological and trophic conditions. The present study shows that a climatic signal in the 2H/1H ratio of peat samples is completely dominated by the direct effects of the spectrum of plants. In addition, the variation in the duration of the growing season in different climatic periods may have had a considerable influence on the 2H/1H ratio of the peat‐forming plants.
The accumulation and the effect of heavy metals on the water fern Azolla filiculoides
Authors: SELA MORDECHAI , GARTY JACOB , TEL‐OR ELISHA
Published: April 2006

Azolla filiculoides Lamarck grown for 3‐7 days in nutrient media containing 8‐15 ppm of different heavy metals was found to contain about 10000 ppm cadmium, 1990 ppm chromium, 9000 ppm copper, 9000 ppm nickel and 6500 ppm zinc. The content of heavy metal in the roots was two‐ to five‐fold higher than in the shoots, and 98% of the heavy metals were bound to the insoluble fraction of the Azolla. The content of heavy metals in dead dried Azolla was 3–7 times higher than in the living plants. Zinc and cadmium were more readily transferred from the roots to the shoots than nickel, copper and chromium. Growth in the presence of the heavy metals resulted in severe leakage of K+, Mg2+ and Na+ ions from the roots with less leakage of Ca2+. The effect of heavy metals on the loss of K+, Na+ and Mg2+ from the shoots was more limited. Nitrogenase activity was almost completely inhibited by cadmium, nickel and zinc, while copper and chromium had less effect. Azolla may prove useful in the detoxification of industrial effluents.
Interactions between ozone and plant cuticles
Authors: KERSTIENS GERHARD , LENDZIAN KLAUS J.
Published: April 2006

The flux of ozone to plant surfaces results in its decomposition at the surface and its uptake through the cuticle. Ozone deposition velocity and ozone permeance were determined for a variety of isolated plant cuticles. Ozone deposition velocity was lower than determined with whole plants kept in darkness. It declined continuously during exposure to the gas and showed a‘recovery’effect after an interruption of the fumigation. It increased with the moisture content of the cuticles and decreased when the ozone concentration in the surrounding air was raised. The deposition velocity was much higher than cuticular ozone permeance at equivalent ozone concentrations. Due to the ozone decay in the cuticle, ozone permeance was much lower in thick than in thin cuticles. Even with the most permeable cuticles, ozone uptake under natural conditions is smaller than the flux through open stomata by a factor of at least 10000.
Reproductive traits and accumulation of nitrogen and phosphorus during the development of fruits of Protea compacta R. Br. (Calcifuge) and Protea obtusifolia Buek. ex Meisn. (Calcicole)
Authors: ESLER K. J. , COWLING R. M. , WITKOWSKI E. T. F. , MUSTART P. J.
Published: April 2006

Protea compacta R. Br. and P. obtusifolia Buek. ex Meisn. are closely related, non‐sprouting serotinous shrubs occurring on the Agulhas Plain, South Africa. The former grows in highly infertile acidic sands and the latter in more fertile alkaline sands. These species were used in a comparative study designed to explore the role of soil type as a selective factor in the evolution of seed size, number and nutrient content. The calcifuge P. compacta had larger seeds with higher N and P content but a lower annual seed production than the calcicole P. obtusifolia. It is proposed that P. compacta exhibits a trade‐off between seed and crop size since it requires larger, more nutritious seeds to establish in the infertile soils. In both species the accumulation of high concentrations of nitrogen and phosphorus in developing infructescenes (cones) was delayed until seed ripening. The significance of this for ecosystem losses of N and P, associated with flower and cone harvesting, are discussed.
Factors controlling the distribution of Tilia cordata Mill at the northern limits of its geographical range
Authors: PIGOTT C. D.
Published: April 2006

The ages of trees of Tilia cordata Mill in the Lake District, which is close to the northern limit of the species in Britain, have been estimated by three methods. Estimates for the few old maiden trees are based on extrapolation of the relation between the diameter of the stem at 1‐3 m above the ground and the known age of planted trees. The diameter of young coppice‐stools is shown to be 1.8 times the diameter at 1.3 m above the ground of trees at the same age; this ratio is applied to large circular stools and their age then estimated. The age of stools with exposed roots has been estimated from measurements of the depth of exposure and of the recent rate of erosion. All three methods show that the age of many trees is of the order of 1000 years. There is therefore the possibility that they became established during earlier periods which were warmer than at present, such as that between A.D, 1 150 and 1300.
A succession to ombrotrophic bog in the Gwent Levels, and its demise: a Welsh parallel to the peats of the Somerset Levels
Authors: SMITH A. G. , MORGAN LORRAINE A.
Published: April 2006

Vegetational history in the period 7000–3000 years ago is described at two adjacent locations in the intertidal zone of the Gwent Levels. The evidence, which bears mainly on the succession of peat‐forming communities, is taken from stratigraphy, lithology, pollen, and plant macro‐remains. The sequences are dated by means of calibrated radiocarbon dates.

At about 6900 B. P. (before present), Phragmites swamp was established on estuarine clay, probably succeeding salt marsh at the higher of the two sites. By about 6700 B. P., after a pioneer phase involving colonization by willows, alder carr was coming into existence. This persisted as a stable community for some 600 years. During its existence there was a minor marine incursion which had little overall effect. There was then a retrogressive succession to reedswamp, probably brought about by an increase of water level, possibly related to changes of tide levels in the Bristol Channel. Phragmites was succeeded by Cladium mariscus (L.) Pohl. as the water became shallower. This was in turn succeeded by a drier fen‐meadow or fen‐grassland but no recolonization by willows or alder ensued. The lack of renewed carr development may have been due to depletion of mineral nutrients. The reedswamp and fen stages lasted for some 300 years overall. The role of oak remains problematic and requires further investigation. The fen gave way to ombrotrophic bog at about 5750 B. P. Via a‘transition bog’stage . The raised bog, which was the culmination of the succession, was annihilated by renewed deposition of estuarine sediments at about 3400 B. p.

The discussion sets the succession on the Gwent Levels in the context of general considerations about postglacial hydroseres and makes a comparison with the history of the Somerset Levels. A Neolithic farming phase is compared with those previously described from the north‐east of Ireland (Pilcher et al., 1971). The Goldcliff phase has three stages of comparable age and duration, but differs in having cereal type pollen in the second stage following the elm decline rather than the first.
Reproductive biology of wild and cultivated carrot (Daucus carota L.)
Authors: KOUL PUSHPA , KOUL A. K. , HAMAL I.A.
Published: April 2006

The wild and cultivated forms of Daucus carota L. are andromonoecious and protandrous. The separation of male and female phases is complete at the level of the Mower and the umbel, but the two phases overlap at the level of the full plant, Creating conditions for geitonogamy. At the same time, insect visits between umbels of adjacent plants lead to xenogamy. The extent of overlap between the male and female phases of various umbel orders varies between wild and cultivated carrot. Consequently, there is probably more outbreeding in wild carrot. The chiasma frequency is higher in cultivated carrot. These findings indicate that the meiotic system generates more variability in cultivated carrot whereas the breeding system has the potential to generate greater variability in the wild plant.
Inter‐and intraspecific variation in seed mass in seven species of umbellifer
Authors: HENDRIX STEPHEN D. , SUN I‐FANG
Published: April 2006

Patterns and causes of inter‐and intraspecific variation in individual seed mass were‐investigated in three prairie and four woodland species of perennial umbellifer. Except for Cryptotaenia canadensis, seeds from woodland species were significantly heavier than those from prairie species. Within species, the magnitude of variation in individual seed mass ranged from three‐to 16‐fold. All the distributions of individual seed masses for the seven species were significantly leptokurtotic and except for Osmorhiza longistylis, all were significantly skewed. Variation between plants was significant in one prairie species (Oxypolis rigidior) and all woodland species. Mean seed mass in a plant was significantly correlated with plant size in three species. Within plant variation in seed mass accounted for 52‐98% of total variation. No one factor consistently affected intraspecific variation in seed mass, although seed number per umbel, timing of umbel production and location of umbel were all important for at least one species. It is postulated that intraspecific variation in seed mass is the rule rather than the exception because of the influence of developmental factors such as seed number, timing of inflorescence production and location of different inflorescences. However, these factors may act in conflicting directions, making it difficult to assign causality to within plant variation in seed mass.
Longitudinal and transverse profiles of K+ and Cl− concentration in ‘low‐’ and ‘high‐salt’ barley roots
Authors: HUANG CHENG X. , Van STEVENINCK REINHARD F.M.
Published: April 2006

summary

The concentrations of K+ and Cl− in meristematic and differentiated cells of barley (Hordeum Vulgare. L. ev. California Mariout) roots were determined by means of quantitative X‐ray microanalysis. In roots of seedlings grown in 0.5 mM CaSO4 (‘low‐salt’ roots), the mean cytoplasmic K+ concentration of meristematic cells was 194 mM, while the average vacuolar concentrations at 10, 50 and 100 mm from the root tip were 62,25 and 22 mM, respectively. Such marked differences in vacuolar K+ concentration of differentiated cells were not found in roots of seedlings grown in full strength Johnson solution (‘high‐salt’ roots). Thus the maintenance of K+ at a relatively high concentration in the cytoplasm of meristematic cells of ‘low‐salt’ roots appears to be a priority requirement. The mean Cl− concentration in the cytoplasm of meristematic cells of ‘low‐salt’ roots was 4.6 mM, and the vacuolar Cl− concentration declined towards the root base. These measured concentrations are compatible with previous data, indicating that X‐ray microanalysis of fully‐hydrated samples, used together with colloidal graphite mixtures as standards, provides a reliable means of measuring ion concentrations at the subcellular level.
Effects of nutrients on the distribution of dry mass, nitrogen and phosphorus in seedlings of Protea repens (L.) L. (Proteaceae)
Authors: WITKOWSKI E. T. F.
Published: April 2006

summary

The response of seedlings of the sclerophyllous shrub, Protea repens (L.) 1., to increasing concentrations of phosphorus (P), nitrogen (N) and a mixture of all essential nutrients excluding N and P (M) was determined in potted Clovelly soil collected Irotn a lowland fynbos site at pella, south‐western Cape, South Africa. Pot culture resulted in increased soil mineral nitrogen, in particular nitrate, and decreased available (resin‐extractable) phosphorus concentrations compared to field soil. High amounts of N (4–64 g m2 N) and M addition resulted in seedling mortality. Plant dry mass, leaf area and phosphorus and nitrogen contents increased in response to increasing application of N, but no significant differences were found in response to M. Increasing applications of N resulted in reduced plant dry mass, leaf area and phosphorus content. These patterns of mortality and growth are interpreted as a response to an imbalance between nitrogen and phosphorus availability. These results are compared to the response of mature fynbos shrubs to fertilizer additions in the field and the responses of pot‐sclerophyllous plants from other Mediterranean‐type ecosystems.
Carbon partitioning patterns of mycorrhizal versus non‐mycorrhizal plants: real‐time dynamic measurements using 11CO2
Authors: WANG G. M. , COLEMAN D. C. , FRECKMAN D. W. , DYER M. I. , McNAUGHTON S. J. , AGRA M. A. , GOESCHL J. D.
Published: April 2006

summary

Gas exchange and carbon allocation patterns were studied in two populations of Panicum coloratum, an Africa C‐4 grass. The plants were grown in split‐root pots, containing partially sterilized soil, with one side either inoculated (I) or not inoculated (NI) with a vesicular arbuscular (VA) mycorrhizal Fungus, Gigaspora margarita. Net carbon exchange rates (CER) and stomatal conductances were measured with conventional gas exchange apparatus, and carbon assimilation, translocation, and allocation were measured using photosynthetically‐fixed 11CO2.

Mycorrhizal infection on one half of the split‐root system caused a 20%, increase in CER. The effect on CER was less in tillers on the opposite side of the plants from the infected half of the roots. The rate at which photosynthates were stored in the leaves was 45% higher. Sink activity (concentration of labelled photosynthates in stem phloem tissue) more than doubled in 1 versus NI plants. CER and stomatal conductances, along with most of the carbon allocation patterns, were nearly identical between the NI (control) high grazing and low grazing ecotypes. However, VA mycorrhizal fungi caused a greater storage of photosynthates in the low grazing ecotype.
Ectomycorrhizal mediation of competition between coniferous tree species
Authors: PERRY D. A. , MARGOLIS H. , CHOQUETTE C. , MOLINA R. , TRAPPE J. M.
Published: April 2006

summary

To test the effect of ectomycorrhizal fungi (EMF) on interactions between host plants, Pseudotsuga menziesii (Mirb.) Franco and Pinus ponderosa Dougl. ex. Laws., seedlings were grown in replacement series in pasteurized soil with (a) no EMF added, (A) two EMF species added ‐ Rhizopogon vinicolor Smith (specific to Douglas‐fir) and R. ochraceorubens Smith (specific to pine), and (c) tour EMF species added ‐ the two Rhizopogon species plus two host generalists, Laccaria laccata (Scop, ex Fr.) Bk. & Br, and Hebeloma crustuliniforme (Bull.) Quel. A replacement series in unpasteurized forest soil also was included. Seedlings without added EMF were colonized by the greenhouse contaminant, Thelephora terrestris. Without added EMF (but with T. terrestris), the tree species mutually inhibited one another, producing Relative Yield Totals significantly < 1; with EMF added, mutual inhibition disappeared. With four EMF species added, Pseudotsuga menziesii seedlings were significantly larger in mixture than in monoculture, with no corresponding decrease in the size of Pinus ponderoso seedlings; this was due solely to seedlings with L. laccata, which apparently enhanced nitrogen (N) and phosphorus (P) uptake by Pseudotsuga menziesii at the expense of luxury consumption by Pinus ponderosa. Graphical analysis suggested that better growth of Pseudotosuga menziesii in mixture with EMF added was related to improved P nitrogen. Both N and P nutrition of Pinus ponderosa was better in mixture with two than no EMF species added; there was no clear nutrient effect with four EMF species added. Results indicate that EMF can reduce competition between plant species and perhaps increase overall community P uptake. However, patterns were specific to both EMF and tree species and were quite different in unpasteurized soils. Hence generalizations about the effects of EMF on plant‐plant interactions must be made cautiously.
Ultrastructural evidence for the identity of some multinucleate rhizoctonias
Authors: WILLIAMS P. G. , THILO E.
Published: April 2006

summary

The ultrastructure of the pore cap in ten multinucleate rhizoctonias, endophytes of non‐orchids and of Microtis (Orchidaceae), was compared with that in isolates of four Sebacina species. The pore cap in all the rhizoctonias was an imperforate, disc‐like structure, Slightly smaller in diameter than the flange forming the septal pore canal. The cap was formed by two Bat lamellae continuous with, but more electron‐dense than, the membranes of the endoplasmic reticulum. The lamellae enclosed a lumen containing a deposit of electron‐dense material. The pore cap in the rhizoctonias was indistinguishable from that in an isolate of Sebacina vermifera Oberwinkler. In contrast, the pore caps in isolates of S. calcea (Pers.: Fr.) Bres., S. umbrina Rogers and S. grisea (Pets.: Fr.) Bres., which were also imperforate and contained a band of electron dense material, were strongly dome‐shaped and extended from one side of the flange to the other.
Electrophoretic variation in a population of the lichen Peltigera rufescens (Weis.) Mudd
Authors: BROWN D. , CURETON‐BROWN M. M. , KERSHAW K. A.
Published: April 2006

summary

Isoelectric focusing was used to investigate the distribution of enzymes exhibiting phosphoglucose isomerase, phosphoglucose mutase, malate dehydrogenase, esterase, hexokinase, glucose‐6‐phosphate dehydrogenase, peroxidase and fructose‐1,6‐bisphosphatase activities in a central Ontario population of the lichen Peltigera rufescens (Weis) Mudd. Samples of thalli were collected in order to estimate enzymatic variation in thalli collected within a site (separated by distances of 1–10 m) and between sites (separated by 5–15 km). A total of 85 different enzyme bands were identified in the 27 samples analysed. The results indicated that, at some locations, within site variation was as large as between site variation. The importance of this variation in the design of physiological studies of lichens is discussed.
Investigation of genetic transfer between strains of the basidiomycete, Stereum hirsutum, using molecular and morphological criteria
Authors: BEECHING JOHN R. , AINSWIRTH A. MARTYN , BROXHOLME S. JOHN , PRYKE JANET A. , RAYNER ALAN D. M.
Published: April 2006

Summary

Pairings between strains of Stereum hirsutum (Willd. ex Fr.) S. F. Gray pp 2% malt agar were analysed using changes in mycelial morphology and non‐self recognition properties as evidence of genetic transfer between the participants. In some combinations the morphological evidence suggested the‐ uniform emergence of a heterokaryon following mating and reciprocal nuclear migration between two compatible homokaryons. In other combinations there was evidence of strongly selective invasion by one of two nuclear types from a heterokaryon into a homokaryon, and in a third type of pairing there was evidence for acquisition by a homokaryon of a second mating type but not an entire nuclear genome.

Combinations representing each of these three apparent classes of genetic transfer were selected, and mycelia grown from single hyphal tips and/or basidiospores taken either from pure cultures of the progenitor strains or from subcultures from interacting colonies. The DNA from each of these mycelia was extracted and analysed using restriction fragment length polymorphisms to detect genomic differences between strains. The results were consistent with the interpretation of events based on morphological criteria. The combination of morphological and molecular approaches holds considerable potential for rapid, yet precise investigation of genetic exchange between fungal strains isolated from natural populations which have not been the subject of extensive genetic analysis by classical means.
Ericoid mycorrhizal fungi in the Myxotrichaceae and Gymnoascaceae
Authors: DALPÉ Y.
Published: April 2006

Summary

Ten species of Byssoascus, Myxotrichum and Pseudogymtioascus (Myxotrichaceae) and (Gymnascella (Gymnoascaceae) were tested for their ability to form ericoid mycorrhizas with axenically grown Vaccinium angmtifolium seedlings. Positive results were obtained with Myxotriclium setasmn and Gymnascella dankalienst's, both of which form Oidiodendron anamorphs and with PseudogypmoOSCUS roseus, a species with a Geomyces anamorph.
The biology of mycorrhiza in the Ericaceae
Authors: LEAKE J. R. , READ D. J.
Published: April 2006

Summary

The role of mycorrihizal infection in the calcium nutrition of Calluna vulgaris (L.) Hull is investigated. Calluna plants were grown in the infected (M) and uninfected (NM) condition m sand supplied with nutrient solutions containing one of the three ecologically important calcium salts: CaSO4, CaCO3, and CaCl2, each supplied over a range of concentrations from zero to 1000 μg ml−1. The influence of infection upon growth and Ca content of whole plants, shoots and roots were determined.

Yields of M plants were significantly larger than those of NM on each of the Ca sources. These differences were particularly marked at the lowest concentrations of applied Ca. Root growth of M plants was strongly enhanced in all Ca treatments, so that the root/shoot ratios of these plants were consistently greater than in those which were NM. M plants also had consistently higher Ca concentrations in their shoots than their NM counterparts. Shoot concentrations were 32, 60, and 23% higher in M than NM plants grown on CaCl2, CaCO3, and CaSO4 respectively. Similarly, mean total Ca contents were 29, 77 and 87% higher in M than XM plants on CaCl2, CaCO3, and CaSO4, respectively. Improved growth of infected plants at high concentrations of applied CaCO3 appeared to be due to alleviation of CO3 toxicity.

The complex interactions involving the direct nutritional effects of Ca ions, the indirect effects of its associated anions, and of other ionic species, notably H+, Al3+ and Fe2+ are discussed.

It is concluded that the principal effect of infection at low exogenous Ca concentrations is to increase the efficiency of Ca capture whereas at high concentrations it is to alleviate toxicity of some auxiliary anions.
The ultrastructure of the placenta in Sphagnum
Authors: LIGRONE R. , RENZAGLIA K. S.
Published: April 2006

summary

The placenta of two Sphagnum species was examined by electron microscopy. In contrast to all mosses so far investigated, neither sporophyte nor gametophyte placental cells of Sphagnum develop wall ingrowths. The sporophyte cells are highly vacuolate and the gametophyte cells close to them degenerate to produce a system of spaces filled with mucilage. Whether this type of placenta represents a primitive or derived condition in mosses is discussed.
Ecophysiology of xerophytic and halophytic vegetation of a coastal alluvial plain in northern Venezuela
Authors: LEE H. S. J. , LÜTTGE U. , MEDINA E. , SMITH J. A. C. , CRAM W. J. , DIAZ M. , GRIFFTHS H. , POPP M. , SCHÄFER C. , STIMMEL K.‐H. , THONKE B.
Published: April 2006

summary

The terrestrial CAM plant Bromelia humilis was examined in the salinas of the Ciénega el Ostional, on the north coast of Venezuela, in the rainy and dry seasons. Three colour forms were distinguished; yellow (in full sun), green exposed (also in sun) and green shaded (beneath woodland). Plant size decreased with increasing irradiance.

An examination was made of the three phenotypes in terms of CO2 exchange (Jco2), dawn‐dusk changes in titratable acidity (ΔH+) and malate and citrate levels, osmotic pressure, xylem tension, sugar and amino acids levels, nitrogen and ion concentrations and ambient temperature fluorescence.

All phenotypes exhibited lowered Jco2 and ΔH+ in the dry as compared to the rainy season. Citrate, as well as malate, showed dawn‐dusk fluctuations. Soluble sugars were the major source of carbon skeletons for nocturnal organic acid production. The dawn‐dusk changes in osmotic pressure were negligible.

Yellow plants performed poorly in contrast to shaded plants in both seasons. The former showed higher dawn‐dusk changes of citrate levels and contained much less nitrogen than shaded plants. Nocturnal recycling of respiratory CO2 was more important in yellow plants and, in the dry season, reached 87%. These differences were reflected in the overall productivity, shaded plants showing increases in size whereas yellow plants utilized energy mainly for leaf replacement.

Water availability and nitrogen supply appear to be the overriding factors determining higher productivity and CO2 assimilation in partially shaded plants as compared with plants in full sun.