bluuebunny/crossref_metadata_2025_split huggingface dataset:
The biology of mycorrhiza in the Ericaceae
Authors: LEAKE J. R. , READ D. J. 
Published: April 2006

SummaryThe 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

summaryThe 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

summaryThe 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.
Ecophysiology of xerophytic and halophytic vegetation of a coastal alluvial plain in northern Venezuela
Authors: GRIFFITHS H. , SMITH J. A. C. , LÜTTGE U. , POPP M. , CRAM W. J. , DIAZ M. , LEE H. S. J. , MEDINA E. , SCHäfer C. , STIMMEL K.‐H. 
Published: April 2006

summaryA comparison of the performance of two epiphytes with crassulacean acid metabolism (CAM) was made during the rainy season and dry season at the Ciénega el Ostional, Chichiriviche in northern Venezuela. The epiphytic bromeliad, Tillandsia flexuosa has water‐retaining tanks and leaf trichomes, and propagates mainly vegetatively to produce large populations in the shrubby island vegetation. The epiphytic orchid, Schomburgkia humboldtiana formed smaller populations, and had large succulent leaves with uniform chlorenchyma and no distinct water‐storage parenchyma, unlike T. flexuosa. Both epiphytes were myrmecophilous.Leaf succulence (kg m−2) declined by ∼ 10% in the dry season for both plants. Both epiphytes showed reduced CO2 uptake during Phase I (dark period) and (dawn‐dusk) titratable acidity (ΔH+) in the dry season. Water‐use efficiency (WUE) was higher for S. humboldtiana (16.0 × 10−3 mol CO2 per mol H2O compared with 5.0 × 10 −3 for T. flexuosa) although WUE remained constant during rainy and dry season for each species.Sixty to seventy per cent of the dawn dusk titratable acidity was derived internally from respiratory CO2 (recycling) for both species, and in absolute terms, recycling decreased in the dry season, in contrast to the expected progression under drought stress. Recycling is an important facet of carbon balance for both species in both rainy and dry seasons.Leaf Na+ concentration was higher than values quoted for terrestrial salt stressed CAM plants. Fructose and glucose declined in leaf bases of T. flexuosa during the dark period, but not in the more distal regions of the leaf. S. humboldtiana showed a decrease in sucrose at night, and mannitol was also an important constituent of the leaves.Xylem sap tension maxima increased from 0.38 ± 0.09 MPa (rainy season) to only 0.55 ± 0.06 MPa (dry season) for T. flexuosa, these values being much lower than those found for terrestrial shrubs and herbs at the same site, the two epiphytes use CAM in conjunction with differing morphological adaptations to maintain growth throughout the year at the Ciénega el Ostional, but it would seem that T. flexuosa has better physiological characteristics for maintenance of carbon acquisition during the dry season.
Occurrence of fructans in the Gramineae (Poaceae)
Authors: SMOUTER HENK , SIMPSON RICHARD J. 
Published: April 2006

summaryThe occurrence and type of storage carbohydrate (fructan, starch or sucrose) was determined in stems of reproductive tillers of a number of species of the family Gramineae representing major taxonomic groups. Plants were collected from two grassland sites in Victoria (Australia). Fructans were detected in all species examined, but particularly high concentrations were found in species of the subfamily Pooideae where fructans accounted for 75–95% of the storage carbohydrates. In most other subfamilies, fructans varied between 5 and 30% of the storage carbohydrates. However, fructans accounted for 50% of the storage carbohydrates in species of the subfamily Arundinoideae. Separation of fructans (to DP 14) by thin‐layer chromatography demonstrated that different isomers of trisaccharides and different proportions of oligosaccharides were present, depending on the species. In some species there was evidence of continuous series of oligosaccharides between sucrose and high molecular weight polymers. However, these series differed markedly from the series of oligosaccharides present in Helianthus tuberosus.The polymerization of fructans and trisaccharide forms present in the grasses examined were similar on generic and, in a number of cases, subtribal and tribal levels and reflected phylogenetic relationships between taxa. The possible presence of fructans in all subfamilies may indicate that fructan synthesis is not necessarily exclusive to the subfamily Pooideae.
Sugar unloading in roots of Ricinus communis L.
Authors: CHAPLEO S. , HALL J. L. 
Published: April 2006

summaryAcid invertase (EC 3.2.1.26) is present in soluble and insoluble preparations from root and shoot tissue of Ricinus communis L. Greatest activity is found in expanding tissue, whilst very low activity is found in vascular and in Phloem‐enriched tissue from stem internodes. In most tissues less than 20% of the total acid invertase activity is insoluble, the exception being extrafloral nectariess where 65–82% is insoluble. The activity of sucrose synthase (EC 2.4.1.13) is low in leaves and apical regions of the primary root; the root stele contains greater activity than the cortex. Considerable diel variations in leaf carbohydrate content were demonstrated and the results suggest that variations for the young sink leaves might be out of phase with those of source leaves by as much as one Photoperiod. The results are discussed m relation to the metabolism and transport of sucrose, particularly in roots.
The activity and preliminary characterization of peroxidases in leaves of cultivars of date palm, Phoenix dactylifera L.
Authors: BAAZIZ M. 
Published: April 2006

summaryPeroxidase activity was determined in leaves of 13 cultivars of date palm, Phoenix dactylifera L. Levels of Peroxidase in the crude extracts were found to differ significantly among the cultivars. The desalted 50–95% ammonium sulphate cuts of the crude peroxidase showed differences in heat inactivation. In studying the effect of assay pH on the activity of peroxidase, 6 of the 13 cultivars examined demonstrated a pH optimum at pH 4.6. Three other pH optima, 4.0, 5.0 and 5.6 were shown for 2, 3 and 2 other cultivars, respectively. Two anodic bands of peroxidase were present in all cultivars, when polyacrylamide gel electrophoresis was carried out and followed by staining the gels with guaiacol as substrate. The two anodic peroxidase bands showed little differences on the oasis of their relative mobility. Both of them were characterized by low electrophoretic mobility. The results are discussed with respect to the possible relationship of the peroxidase activity in the vascular fusariosis (Bayoud disease) of the data palm.
Cytology and development of a mycorrhiza‐like infection in the gametophyte of Conocephalum conicum (L.) Dum. (Marchantiales, Hepatophyta)
Authors: LIGRONE R. , LOPES C. 
Published: April 2006

summaryAn aseptate fungus associated with the gametophyte of the hepatic Conocephalum conicum (L.) Dum. was studied by light and electron microscopy. The fungus forms a highly branched mycelium external to the plant. Fungal hyphae colonize the smooth‐walled rhizoids, through which they pass into the gametophyte parenchyma of the midrib. The fungus in the parenchyma is entirely intracellular. Vesicles are found in rhizoids and a few ventral layers of parenchyma cells. Prominent arbuscules develop in more internal cells from lateral branches of infecting hyphae that spread from cell to cell. Infected host cells show cytoplasmic proliferation, especially of ribosomes, Plastids and mitochondria, The arbuscules eventually degenerate leaving clumps of collapsed hyphae. Reinfection of cells with degenerate arbuscules was not observed. The ultrastructural and developmental characteristics of the fungus and its high cytological compatibility with the host are indicative of a well integrated symbiotic association similar to the vesicular–arbuscular mycorrhizas of higher plants.
The development of endomycorrhizal root systems
Authors: AMIJEE F. , TINKER P. B. , STRIBLEY D. P. 
Published: April 2006

summaryLeek plants (Allium porrum L.) were grown in a controlled environment on a mixture (2: 1 w/w) γ‐irradiated (1.0 Mrad) sandy loam and sand, at six concentrations of bicarbonate‐soluble phosphorus (P) ranging from 22 to 344 mg P kg−1 (soil basis). Inoculum of the vesicular‐arbuscular (VA) mycorrhizal fungus Glomus mosseae (Nicolson & Gerdemann) Gerdemann and Trappe was placed (M) or not (NM) in a layer 3 cm below the soil surface.At intervals of 10 d, lengths of main axes of roots and their lateral branches, and of the segments of infection within them, were measured. From these data we calculated the mean (harvest interval method} rates of linear extension of root tips and of infection fronts for each member of root, averaged over the whole root system. The mean delay, d, between a root encountering the layer of inoculum and the subsequent formation of internal infection, was also derived.Addition of P to soil did not affect rates of extension of roots, but increased the initiation of main axes and laterals. Infection segments extended twice as fast in laterals as in main axes. At low rates of addition, P did not affect fungal behaviour but increased the length of root available for colonization.When bicarbonate‐soluble P exceeded 140 mg kg−1, the rates of extension of infection fronts in both main axes and laterals were approximately halved, and d was considerably increased. The density (the area ratio of fungal to host tissue in a longitudinal squash) of the hyphae and arbuscules respectively, and the number of entry points per unit length of root, were greatly reduced by added P. However, the ratios of numbers of entry points/hyphal density and of arbuscule density/hyphal density were unaltered, and the morphology of the fungus was not noticeably affected.It is probable that formation of entry points was the rate‐limiting step for colonization, and that this rate was reduced by added P.
Response of white clover (Trifolium repens L.) and ryegrass (Lolium perenne L.) to acid rain in situations of species interferences
Authors: MENCHACA L. , HORNUNG M. 
Published: April 2006

summaryPure stands of Trifolium repens L. N.Z. Huia and Lolium perenne L. S32 and mixtures of various densities and frequencies were treated with sulphuric acd solutions of pH 2.5, 3.5 and 5.6. The species yield was recorded over five sequential harvests. Multifactorial response equations were used to describe the behaviour of the species yield as a function of acidity and the density of both species. Predictions, made through these models, showed that the response of yield of these species to simulated acid rain treatments Varied greatly depending on the planting density, the time of harvesting and on whether the plants were growing in monoculture or in mixture. This suggests that it is not sufficient to consider the effects of experimentally applied acid rain on single individuals or low density stands, since the results obtained will not reflect the response in a close canopy sward.
Growth dynamics and water use of seedlings ofQuercus albaL. in CO2‐enriched atmospheres
Authors: NORBY RICHARD J. , O'NEILL E. G. 
Published: April 2006

summaryWhite oak (Quercus albaL.) seedlings were grown from a half‐sib collection of acorns in pots containing a nutrient‐Poor forest soil and maintained in controlled‐environment chambers having mean atmospheric CO2concentrations of 389, 496, and 793 cm3m−3. Additions of nitrogen and phosphorus to the soil increased plant growth, indicating that the unfertilized plants were nutrient deficient. Despite the nutrient deficiency, the plants grown in elevated concentrations of CO., generally were larger than those in ambient CO2, but dry weight data from harvests at 5, 12, 24, and 36 weeks provided insufficient evidence of an effect of CO2because of the high variability associated with the recurrently‐Hushing habit of these seedlings. Mathematical growth analysis based on periodic non‐destructive measurements allowed comparisons of the continuous growth patterns of the plants and avoided the problems of ontogenetic variation. CO2, enrichment was thus shown to increase plant growth rate primarily through increased unit leaf rate rather than increased leaf area production. Unit leaf rate during the second half of the experiment was 22 and 27% higher in the medium and high concentrations of CO2compared with that in low CO2instantaneous measurements of foliar gas exchange also showed that CO2, assimilation increased with CO2, enrichment. The most pronounced effect of CO2, enrichment was increased water‐use efficiency, which was shown both through whole‐plant gravimetric analysis and instantaneous gas exchange measurements. Whole‐plant water‐use efficiency for the duration of the experiment was increased by 52 and 82% by the mdium and high concentrations of CO2. Limitations of resources, including water and nutrients, do not preclude plant growth responses to CO2enrichment of the atmosphere.
Holocene to Middle Last Glaciation vegetation history at Newall Creek, western Tasmania
Authors: VAN DE GEER G. , FITZSIMONS S. J. , COLHOUN E. A. 
Published: April 2006

summaryPollen analysis and 14C dating of 5.5m of organic‐rich soil and fluviatile deposits from Newall Creek (altitude 140 m) indicate that temperate rainforest (0‐11 K yr B.P.) was preceded by grassland‐herbland (11 to 21 K yr B.P.), and then by open grassy Eucalyptus woodland.Comparison with a lake‐swamp site at Tullabardine Dam showed that the main vegetation changes were comparable making allowance for some spatial variations in the taxa represented and the lower quantity of pollen in the fluviatile deposits.The inferred sequence of climatic change was from a cool moist interstadial through a cold last glacial maximum to a warm moist Holocene environment, a sequence also indicated at Tullabardine.
Occurrence of nodulation in the Leguminosae
Authors: DE FARIA S. M. , LEWIS G. P. , SPRENT J. I. , SUTHERLAND J. M. 
Published: April 2006

summaryReports of nodulation in the Leguminosae are examined in the light of current views on the taxonomy of the family. In the subfamily Caesalpinioideae, nodulation is largely restricted to the tribe Caesalpinieae and the genus Chamaecrista from the Cassieae. All nodules studied have rhizobia retained within infection threads during the nitrogen fixing period.In the Mimosoideae, nodulation is general, except for 4 groups within the tribe Mimoseae, and a very few species of Acacia. The only tribe from the Papilionoideae which appears not to nodulate is the Dipterygeae, although the monogeneric Euchresteae has not been examined. A number of genera in the Swartzieae do not nodulate. Taking tile family as a whole, nodulation appears to be very uniform – certain sections nodulate, others do not.
Responses to high temperature of the Azolla–Anabaena association, determined in both the fern and in the cyanobacterium
Authors: WATANABE I. , LIN CHANG , SANTIAGO‐VENTURA TERESITA 
Published: April 2006

summaryThe responses to high temperature of the cyanobacterial symbiont and the host fern in tile Azolla–Anabaena symbiosis were studied by using Azolla strains with heterologous Anabaena azollae Strasburger of without Anabaena. At 26/18°C, symbiotic Azolla grew better than the corresponding Anabaena‐free Azolla. A high temperature‐sensitive species Azolla filiculoides Lamarck, produced smaller biomass under conditions of 37 °C (day)/29 °C (night) than the corresponding Anabaena‐free Azolla grown in N‐containing medium. A. filiculoides with Anabaena from temperature tolerant Azolla microphylla Kaulfuss was more effective at N2 fixation than A. filiculoides with homologous Anabaena. A microphylla with Anabaena from A. filiculoides grew more slowly and fixed less N2 than the strains with homologous Anabaena. In the presence of combined N at 37°/29 °C, A. microphylla grew better than A. filiculoides with Anabaena from A. microphylla. Tolerance of the Azolla‐Anabaena association to high temperature is, therefore, determined both in the host fern and symbiont Anabaena.
The effects of nickel, calcium and magnesium on the acid phosphatase activity of two Alyssum species
Authors: GABBRIELLI R. , GROSSI L. , VERGNANO O. 
Published: April 2006

summaryRoot Surface acid phosphatase activity was assessed in seedlings of two species of Alyssum, one endemic to Tuscan serpentines (Alyssum bertolonii Desv.) and the other of wide occurrence (Alyssum saxatile L.), cultivated in solutions to which various concentrations of Ni2+, Ca2+ and Mg2+ were added. Treatments were applied in two factorial experiments of type 2n. A concentration of 0.01 mM Ni2+ markedly stimulated phosphatase activity in A. bertolonii, but slightly decreased it in A. saxatile. Increased Ca2+ concentration stimulated enzyme activity in both species, hut in A. bertolonii the highest activity was obtained with low Ca2+ concentrations, whilst the opposite occured in A. saxatile. A. bertolonii instead required high Mg2+ concentrations to increase phosphatase activity significantly. The same concentrations were toxic to A. saxatile. In the serpentine species, favourable conditions for the increase of phosphatase activity were induced by a high Mg2+/Ca2+ ratio, which also favoured dry mass production. Therefore it is possible that the increase of phosphatase activity might be an aspect of plant adaptation to serpentines.
Effects of O3 on alder photosynthesis and symbiosis with Frankia
Authors: GREITNER CAROL S. , WINNER WILLIAM E. 
Published: April 2006

summary Alnus serrulata (Aiton) Willdenow seedlings with and without root nodules formed by the nitrogen‐fixing actinomycete Frankia were exposed to clean filtered air or ozone (O3) at 0.12 μl l−1 for 27 d (approximately 164 h total exposure). Gas exchange measurements on leaves and transmission electron micrographs of root nodule cells were made to detect any O3 effects on the functioning of leaves and the root symbiont.Photosynthesis, stomatal conductance, and internal CO2, concentration were calculated for all plants in clean O3‐free air more than three weeks after the fumigations began. Significant positive correlations between photosynthesis and conductance were found for leaves of control nodulated and unnodulated alders and O3‐treated nodulated alders. There was a weak positive correlation between photosynthesis and conductance for unnodulated O3‐treated seedlings measured in clean air. When O3‐treated leaves were measured during fumigation with O3, no positive correlation between photosynthesis and conductance was found for either nodulated or unnodulated seedlings. Photosynthetic rates of leaves having the highest stomatal conductance values were decreased by O3for both nodulated and unnodulated plants.Transmission electron microscopy (TEM) revealed that after a 27 d exposure of shoots to O3, host root cells of nodules from O3‐treated plants lacked organelles and showed extensive cytoplasmic breakdown. Hyphae and N2‐fixing vesicles of Frankia appeared normal. The Frankia endophyte seems to be more resistant to O3 than is the host root nodule cell. These results show that ambient levels of O3 may reduce photosynthesis and bring about associated degradation in rhizosphere symbiosis.
The effects of temperature and moisture on CO2 uptake and total resistance to water loss in the antarctic foliose lichen Umbilicaria antarctica
Authors: HARRISSON P. M. , WALTON D. W. H. , ROTHERY P. 
Published: April 2006

summaryMaximum net photosynthesis of field‐fresh thalli, illuminated at 200 μmol photons m−2 s−1 (PAR), was attained at 13 °C and 1.10 g g−1 water content. Small but significant rates of photosynthesis were measured at −5.5 °C. Depression of net photosynthesis at high thallus water contents is explained in terms of thallus anatomy. Calculation of evaporative resistance of the thallus by a new method showed a moisture‐dependent response pattern, and was in agreement with direct observations made on other foliose species.