bluuebunny/crossref_metadata_2025 huggingface dataset:
Utilization of amino acids by the blue-green alga Synechococcus AN (Anacystis nidulans)
Authors: Wallen D. G. , Allan R.
Published: September 2008

The ability of amino acids to support growth of Synechococcus AN when inorganic nitrogen is lacking was tested. Their relative contribution to growth was greater at low (8 μE∙m−2∙s−1) than at photosynthetically saturating irradiances (150 μE∙m−2∙s−1). At low irradiation growth on most amino acids ranged from 70.4 to 88.9% of growth on NO3 N. In contrast, at saturating irradiances, growth on the same amino acids ranged from only 50.7 to 61.2% of growth on NO3 N. The protein concentration of cells grown on the amino acids ranged from 74.6 to 93.7% of the concentration of NO3 N grown cells. Further, cells grown at low irradiances exhibited relatively higher concentrations of chlorophyll a than cells grown at saturating irradiances. The ecological significance of amino acids appears to be in their nitrogen contribution to the photo-heterotrophic growth of blue-green algae. The enhanced contribution under conditions of low irradiances and limiting inorganic nitrogen would counteract, in part, the effect of low irradiances on photosynthesis possibly enhancing the competitive position of the population.
Differences in the damage caused by glaze ice on codominant Acer saccharum and Fagus grandifolia
Authors: Melancon Serge , Lechowicz Martin J.
Published: September 2008

A severe glaze ice storm had greater destructive impact on Fagus grandifolia than on codominant Acer saccharum trees in a mature southern Quebec forest. Both the numbers and total biomass of major branches lost by beech were significantly greater than by sugar maple compared with the contribution of each species to the canopy composition. This greater ice damage to beech suggests that reciprocal replacement processes involving beech and maple seedlings cannot completely account for the maintenance of beech–maple codominance in northern forests subject to relatively frequent ice storms. We hypothesize that the ability of beech to root sprout is important in compensating for its greater susceptibility to ice damage and contributes to the maintenance of beech–maple codominance in northern forests.
Pollen evidence for the postglacial origins of Nova Scotia's forests
Authors: Green David G.
Published: September 2008

Pollen diagrams from sites in southwest Nova Scotia and close to the New Brunswick – Nova Scotia border show that after retreat of the Wisconsin ice sheets, most tree taxa arrived in the extreme southwest of Nova Scotia earlier than anywhere else in the province. For most tree taxa, arrival times at sites in maritime Canada and in northeastern New England are consistent with very early dispersal of individuals along the coastal strip via the exposed coastal shelf and with their entering Nova Scotia from the southwest. These scattered pioneer populations acted as centres for major population expansions, which followed much later in some cases. Local environments, fire, and interspecies competition appear to have been more important than propagule dispersal rates as factors limiting the spread of most taxa.
A taxonomic study of the "medicagoid" Trigonella (Leguminosae)
Authors: Small Ernest
Published: September 2008

The medicagoid Trigonella are a cohesive group of Old World species of much closer affinity to Medicago than to Trigonella. A numerical examination indicated that these are appropriately placed in two sections, each with a number of perceivable subdivisions. A key and illustrations to the 23 species recognized in this study are presented.
Rhizome architecture for dispersal in Eleocharis palustris
Authors: Routledge R. D.
Published: September 2008

The rhizome architecture of a population of the spike rush, Eleocharis palustris (L.) R. & S., was examined. Its rhizomes were found to display remarkably little branching. Furthermore, the rhizomes turned very little from year to year in their direction of growth. In this paper, these observations are documented and possible evolutionary advantages of such an architecture are explored. Particular emphasis is placed on the hypothesis that the fitness of an individual clone could be enhanced by such a strategy through an increase in the probability of escape from a crowded seedbed.
Responses of Ranunculus sabinei and Papaver radicatum to removal of the moss layer in a high-arctic meadow
Authors: Sohlberg E. H. , Bliss L. C.
Published: September 2008

Within the High Arctic, vascular plants of small size often grow in dense turfs of moss. The effect of moss removal on vascular plant growth was examined over a 2-year period for Ranunculus sabinei and Papaver radicatum. Aboveground non-repoductive parts of flowering R. sabinei were significantly (p < 0.05) larger for individuals in moss removal and moss clipped treatments than those in control plots. Similar but nonsignificant differences were found for nonflowering individuals of R. sabinei. Papaver radicatum had significantly (p < 0.05) larger aboveground, nonreproductive biomass in moss removal and replacement plots than in the moss clipped treatment and the controls. We suggest that the responses of Ranunculus sabinei to moss clipping or removal and of Papaver radicatum to moss removal and moss replacement are examples of the interaction between moss and vascular plants in relation to microsite conditions. Moss turf provides more soil moisture during drought periods as well as higher levels of nutrients. Moss removal results in warmer and more aerated soils. We interpret these results as commensalism rather than competition.
Xylogénèse chez les Dicotylédones arborescentes. V. Formation du bois de tension et transport de l'acide indole acétique tritié chez le Hêtre
Authors: Lachaud Suzanne
Published: September 2008

Upper stems of young beeches (Fagus silvatica L.) were bent into Jaccard loops in May. If they stayed on the tree, they produced a wide arc of extreme tension wood on the upper side of the loop, which contained numerous gelatinous fibers, few vessels, and little axial parenchyma. On the lower side of these loops, xylogenesis was nearly stopped. If bent stems were removed from the tree, xylogenesis was far less asymmetric: the wood formed on the upper side contained normal vessels and axial parenchyma, but also gelatinous fibers; on the lower side, the wood was normal. Transport and metabolism of 3H-labelled indole acetic acid was studied in both models. In intact loops left on the trees, lateral auxin transport took place mainly towards the lower half of the stem. In isolated loops, no preferential direction could be detected for lateral auxin transport. Extreme tension wood differentiation on the upper side of a bent stem requires the intervention of correlative factors, not only from buds, but also from the base of the tree, which particularly influence lateral downward transport of auxin.
Ecological tolerance and niche structure of Sphagnum along a pollution gradient near Sudbury, Ontario, Canada
Authors: Gignac L. Dennis
Published: September 2008

Accumulations of Cu and Ni were measured in four Sphagnum species occupying overlapping niches at varying distances from the smelter at Falconbridge, Ont. A distinct relationship existed between the metal content of Sphagnum russowii and the reciprocal of the distance from the pollution source. Accumulations of Cu and Ni in the partially humidified peat subtending the living Sphagnum were significantly higher than the concentrations retained in the moss plants, particularly on sites having high metal loadings. Concentrations of Cu and Ni were not significantly different between species occupying overlapping height and pH zonations. There existed a significant relationship between metal accumulations in the capitula of Sphagnum russowii, Sphagnum magellanicum, and Sphagnum riparium and the partially humified peat below the living moss.
Evaluation of birdsfoot-trefoil (Lotus corniculatus) regenerated plants following in vitro selection for herbicide tolerance
Authors: MacLean Nancy L. , Grant W. F.
Published: September 2008

Suspension cultures of Lotus corniculatus L., cv. Leo, were treated with the herbicides 2,4-D (2,4-dichlorophenoxyacetic acid) (10–20 ppm) or chlorsulfuron (2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]-benzenesulfonamide) (0.5–1.0 ppb) to select for either herbicide resistance or tolerance. Effects of the selection process on regeneration, pollen, chromosome number, and herbicide sensitivity of regenerates were evaluated. Plantlets regenerated from selective 2,4-D cultures exhibited low in vitro rooting percentage, a high percentage of shrivelled pollen, and variation in chromosome number. The effect of 2,4-D was confounded, in some cases, with the effect of duration of culture period. A slight degree of tolerance was observed in one of the selections to chlorsulfuron at 10 to 20 g ha−1. No sign of tolerance to 2,4-D was observed at 1.0 kg ha−1.
The role of water in the regulation of plant development
Authors: McIntyre Gordon I.
Published: September 2008

It is postulated that the changes in growth and metabolic activity that characterize many features of plant development are produced by the interaction between the hydraulic conductivity of the tissues and the influence of environmental factors, transpiration and osmotic gradients on the uptake, distribution, or loss of water. Mechanisms based on this concept are proposed for six aspects of development. These are (i) seed germination and stem elongation (water uptake), (ii) apical dominance and tropisms (water distribution), and (iii) leaf senescence and abscission (water loss). The postulated mechanisms are based on the hypothesis that water is the factor that normally limits the rate of growth and metabolic activity in the intact plant. The validity of the concept is supported by the unique capacity of water to perform three basic functions. These functions are (i) to mediate environmental effects on growth and metabolism, (ii) to correlate the growth of different parts of the plant, and (iii) to integrate growth and metabolic activity at the cellular level. It is also suggested that the responses induced by the application to plants of certain growth-regulating substances can be mainly attributed to the capacity of these substances to promote the uptake of water.
The effects of amino acids on the growth and sporulation of Verticillium dahliae
Authors: Duncan D. R. , Himelick E. B.
Published: September 2008

Conidial and dry weight production of Verticillium dahliae varied greatly depending on the amino acid used as the nitrogen source in Czapek's–Dox medium. Variable fungal growth was also noted when mixtures of amino acids were used and growth was dependent on the type and concentration of each amino acid in the mixture. Similar variation was obtained when sugar maple (Acer saccharum) sap was amended with individual amino acids. These results are examined in relation to the reported variation in the amino acid content of host xylem sap and in relation to verticillium wilt development.
Differential acclimation potential to low temperatures in two species of Lycopersicon: photosynthesis and growth
Authors: Vallejos C. Eduardo , Pearcy Robert W.
Published: September 2008

The effect of growth temperature on the temperature responses of photosynthesis and on growth as estimated from plastochron measurements of L. esculentum, a high-altitude ecotype of L. hirsutum, and their hybrid was studied. The two species and their hybrid displayed similar temperature responses of photosynthesis when they were grown under a thermo-period of 25:18 °C. However, when the growth temperature was decreased to 12:5 °C, only L. hirsutum and the hybrid showed the ability to acclimate by increasing their photosynthetic rates at low temperatures. Growth exhibited a similar response to a shift to the low-temperature regime since the growth rate of L. esculentum was reduced to a greater extent than that of L. hirsutum. Moreover, L. hirsutum resumed growth at a faster rate after a short period of time, whereas L. esculentum did not. These results show that there are parallel differences in the capacity of photosynthesis and growth to acclimate to low temperatures between L. esculentum and the high-altitude L. hirsutum.
Responses to defoliation in Holcus lanatus, Lolium perenne, and Trifolium repens from three different-aged pastures
Authors: Aarssen L. W. , Turkington Roy
Published: September 2008

The effects of defoliation on biomass distribution were studied in plants of Holcus lanatus L., Lolium perenne L., and Trifolium repens L. collected from three different-aged pastures. Individual plants were cloned and ramets from each clone were subjected to clipped and unclipped treatments over a period of 1 year. In the unclipped treatment for each species, plants from the three pastures showed no differences in the extent of clonal growth (i.e., tiller or stolon production). In the clipped treatment, however, plants from the oldest pasture displayed significantly more extensive clonal growth than plants from the younger pastures. With increasing pasture age, there was a significant trend of increasing compensatory clonal growth in response to defoliation for all three species. This may be interpreted as a consequence of selection pressure from grazing. However, the data do not suggest that the grass–grazer relationship is a mutualism. Alternative interpretations are considered.
Slope, aspect, and slope position as factors controlling grassland communities in the coulees of the Oldman River, Alberta
Authors: Lieffers V. J. , Larkin-Lieffers P. A.
Published: September 2008

Vegetation and environmental variables were examined in some coulees of the Oldman River near Lethbridge, Alta. Principal components analysis of environmental variables indicated that solar energy, aspect, soil Mg2+, [Formula: see text], and moisture were related to the first axis of variation. Slope position, soil [Formula: see text], moisture, K+, [Formula: see text], and amount of bare ground were related to a second axis of variation. There was a large range in species diversity among plots; most diverse plots were on north-facing slopes. Direct ordination of vegetation data indicated that slope position and aspect were most important in describing distribution of species. Koeleria macrantha, Bouteloua gracilis, Stipa comata, and Artemisia frigida were found on most coulee positions. Hymenoxys richardsonii, Machaeranthera grindeloides, Astragalus spatulatus, and Eriogonum flavum were mostly restricted to summit and upper slope positions. Anemone patens, Geum triflorum, Thermopsis rhombifolia, and others were most abundant on north- and east-facing slopes. Fewer species (e.g., the C4 Aristida longiseta and the cactus Coryphantha vivipara) were mostly confined to south-facing positions.
Polygenic modification of a major virulence gene in Ustilago hordei
Authors: Person C. O. , Christ B. J. , Ebba T.
Published: September 2008

The genetics of virulence of two Ustilago hordei (Pers.) Lagerh. races were examined on the resistant barley cultivar Trebi. Tetrad analysis was used to identify segregation patterns. The segregation patterns from the F1 teliospores revealed a single major gene for virulence with high levels of smut inherited as a dominant trait. Parents T1 and T4 were identified as homozygous dominant and homozygous recessive, respectively. Analysis of the F1 teliospores also revealed variation that could not be accounted for by either a one- or two-gene hypothesis. Further analysis of selected sporidia indicated that several genes modified the effects of the major gene.
Life history and allozyme variation in populations of the weed species Setaria faberi
Authors: Warwick S. I. , Thompson B. K. , Black L. D.
Published: September 2008

Life-history features and allozyme variation were examined among and within eight populations of Setaria faberi collected at the northern limits of its distribution range from 39 to 45° N latitude. Statistically significant variation among the eight populations was evident for all 16 characters relating to morphology, phenology, and growth characteristics of the plants. Very low levels of allozyme variation were detected in the eight populations, i.e., only 3 of the 22 loci surveyed were polymorphic. Nine multilocus genotypes were present. Six of the eight populations contained a single genotype, whereas the most variable population (A) contained eight genotypes. Estimates of within-population variation of nine life-history features indicated that population A was the most variable with 7 of 9 characters showing statistically significant among-family variation.
Differential response to competition in weedy biotypes of proso millet
Authors: Warwick S. I. , Thompson B. K.
Published: September 2008

Five weedy biotypes of proso millet (Panicum miliaceum L.) were grown under conditions of both intra- and inter-biotype competition. These biotypes represent the range of weediness from crop-like, large, white-seeded types with dense, drooping panicles to the most weed-like strain, which produces small, dormant, black seeds and has open, shattering panicles. Under noncompetitive conditions, the five biotypes of proso millet (WHITE, GOLDEN, ORANGE, CROWN and BLACK) differ strikingly in plant size, fresh weight distribution patterns, flowering time, and seed size. All biotypes showed decreased biomass per plant and delayed flowering time with increasing density when grown in monoculture. Variation in total biomass among individuals in each biotype was reduced at increasing densities resulting in positively skewed frequency distributions. The crop-like biotypes (WHITE and GOLDEN) demonstrated the greatest intrabiotype competitive effects, i.e., were the least tolerant of increased density in monoculture showing decreased survival and reduced seed weight. When grown in mixed stands, the same two biotypes were found to have the greater competitive ability than the other biotypes in terms of both survival and total standing crop biomass. The contributions of the BLACK, CROWN, and ORANGE biotypes to total biomass in mixed stands were very small. Factors affecting the successful establishment of field infestations of the crop-like and weedy biotypes are discussed.
Ecological relationships of wild rice, Zizania aquatica. 5. Enhancement of wild rice production by Potamogeton robbinsii
Authors: Lee P. F.
Published: September 2008

Production of wild rice in a lake with clay sediment was examined inside and outside clumps of Potamogeton robbinsii (L.). Dry weights of wild rice plants were 10–15 times greater inside than outside these clumps. Analyses of variance of sediment samples revealed that values of loss on ignition, phosphorus, manganese, and zinc were higher inside the clumps of P. robbinsii, while values of bulk density, pH, and water depth were higher outside the clumps. Discriminant analysis was able to separate the samples on the basis of the values of phosphorus, manganese, and zinc relative to bulk density, copper, calcium, and depth. Experiments with various fertilizer treatments under controlled conditions determined that the primary limiting nutrient in the sediment outside the P. robbinsii clumps was phosphorus. It was proposed that as Potamogeton robbinsii decayed, it increased the organic content of the clay sediment, thereby lowering the pH and increasing the availability of nutrients.
The formation of hyaline caudicle in two vandoid orchids
Authors: Yeung Edward C. , Law Sandra K.
Published: September 2008

The development of the hyaline caudicle in two vandoid orchids, Oncidium sphacelatum and a Phalaenopsis hybrid, was studied with the light microscope. These two orchids display similar patterns in caudicle development. In both orchids the hyaline caudicle differentiates from the tapetum. At meiosis a lipoidal substance begins to form in the tapetal cells that are located in a cleft of the pollinium near the junction of the stipe and the pollinium. This synthetic activity gradually spreads to other tapetal cells within the pollinium cleft. The lipoidal product initially appears as small, spherical droplets that collect in the cytoplasm of the tapetal cells. As the pollen matures, these tapetal cells disintegrate and the lipoidal product is then fused to form elastoviscin, the compound from which hyaline caudicles are made. The results of this study indicate an additional non-nutritive role for the tapetum in the production of the caudicle.
Vegetational and climatic history of Nova Scotia. I. Radiocarbon-dated pollen profiles from Halifax, Nova Scotia
Authors: Ogden III J. Gordon
Published: September 2008

Pollen and sediment stratigraphy of three lakes in the Halifax, N.S., area show similarities and differences related to morphometry and hydrology. Five radiocarbon dates from two of the cores provide sedimentation rate estimates ranging from 0.31 to 0.58 mm/year with an r2 of 0.97. Organic sedimentation was initiated in lakes in the Halifax area about 12 000 years ago. Low pollen densities and high proportions of herbaceous and shrub pollen types imply open country or tundra-like vegetational cover until ca. 10 000 B.P. A possible Allerød-type late-glacial climatic oscillation is apparent from the sediment and pollen records. Small birch pollen (cf. Betula nana), pine, spruce, willow, and ericaceous pollen dominate the late-glacial (ca. 12 000–10 000 B.P.) predominantly inorganic section of the sediment cores. It is presumed from the pollen data that hemlock (Tsuga canadensis) invaded the catchment areas about 8000 years ago, and that beech (Fagus grandifolia) arrived about 5000 years ago. Thermophilous Appalachian elements (Nyssa, Carya, Juglans, and Tilia) have never been part of postglacial Nova Scotian forests.
High-affinity phosphate absorption is independent of the root cell wall in Pisum sativum
Authors: Lefebvre Daniel D. , Clarkson David T.
Published: September 2008

The high affinity for phosphate influx by pea root cells was not significantly altered by osmotic shock, plasmolysis, or the preparation of free protoplasts. The Km of normal roots was 7.74 ± 2.14 μM. The Vmax for phosphate uptake was reduced to 64% by osmotic shock and to 38 and 23% by plasmolysis and protoplast isolation, respectively. Efflux analysis indicated that there was a concentration increase for phosphate in the root free space over that of the bathing solution. This apparent binding does not appear to be involved in the uptake affinity of phosphate.
A survey of endosperm starch granules in the genus Hordeum: a study using image analytic and numerical taxonomic techniques
Authors: Baum Bernard R. , Bailey L. Grant
Published: September 2008

Image analysis was used to quantify size of endospermic starch granules in 39 species of Hordeum. A set of 279 samples, each with ca. 25 replicates, representing most species of the genus was analyzed by various multivariate techniques. Two groups can be distinguished. One group consisting of 6 species (H. vulgare, H. spontaneum, H. bulbosum, H. glaucum, H. murinum, and H. leporinum) is characterized by possessing granules greater than 35 μm in diameter and a bimodal distribution of all the sizes. The second group, consisting of the remaining 33 species, had granules less than 35 μm in diameter, unimodally size distributed. Univariate statistics for each species are summarized in box plots and bar diagrams. Some species can be uniquely identified. The usefulness of starch in Hordeum systematics is discussed.
Nature and cause of zonation discreteness around glacial prairie marshes
Authors: Johnson W. Carter , Sharik Terry L. , Mayes Richard A. , Smith Eric P.
Published: September 2008

Species boundary clustering in zoned vegetation was examined along six wetland–upland coenoclines from four prairie marshes in eastern South Dakota that differed in size, permanence, water quality (salinity), topography, and exposure to waves. Vegetation structure and composition were measured from small, contiguous quadrats running through concentric vegetation zones. Rates of vegetation change along coenoclines were estimated using direct gradient analysis, detrended correspondence analysis, and a statistical technique that detects clustering of species' borders. All wetlands exhibited visually distinct zones, but quantitative analysis revealed that vegetation fomed a virtual continuum along the gradient in small wetlands, while near the shorelines of large wetlands both vegetation composition and structure were sharply discontinuous between marsh and meadow zones. This lower border of the meadow zone apparently was sharpened by exposure to waves and ice scour. The upper meadow zone border with prairie vegetation was less distinct but coincided with a sharp change in topography and in subsoil texture. Interspecific competition appeared less important than physical environmental factors in affecting zonation discreteness. The meadow–prairie zone contact approximates the upper limit of influence from wetland processes and is proposed as the wetland–upland border.
Interactions between Sclerotinia sclerotiorum and other fungi on the phylloplane of lettuce
Authors: Mercier J. , Reeleder R. D.
Published: September 2008

Selected fungi recovered from the phylloplane of lettuce were assayed, using in vitro and in vivo techniques, to determine their effectiveness as antagonists of ascospores of the lettuce drop pathogen, Sclerotinia sclerotiorum. On leaf discs, Trichoderma viride, Alternaria alternata, and Epicoccum purpurascens significantly reduced ascospore germ-tube elongation by 34.2, 60.6, and 38.3%, respectively. On whole plants, these three fungi significantly reduced infection by 40–93.3%. Isolates of Cladosporium cladosporioides and a red yeast inhibited ascospore elongation significantly in the in vitro leaf disc assay but failed to provide significant protection against infection by S. sclerotiorum in the in vivo whole-plant assay. Observations with the scanning electron microscope indicated that hyphae of T. viride and A. alternata came into close contact with ascospores on the leaf surface, suggesting parasitic relationships. Hyphae of E. purpurascens did not come into direct contact with ascospores and inhibition may have been due to production of antifungal compounds.
Physiological responses of Vaccinium vitis-idaea to high tissue concentrations of manganese
Authors: Miller P. M.
Published: September 2008

Photosynthetic rates, dry moss accumulation, leaf number per shoot, stem length, and tissue element concentrations were measured in Vaccinium vitis-idaea growing in tussock tundra at Toolik Lake, Alaska. Manganese concentrations of 6 800 – 12 300 μg/g dry mass in leaf tissue of V. vitis-idaea did not affect photosynthetic rates, dry mass, or leaf number when compared with plants containing 18–1500 μg manganese/g dry mass. Tissue analysis indicated possible substitution of manganese for magnesium and inhibition of uptake and (or) translocation of calcium, iron, manganese, silicon, and aluminum. High concentrations of calcium and the high correlation between manganese and silicon concentrations suggest that these elements may play a role in manganese tolerance observed in V. vitis-idaea.
Ultrastructure of the infection of spruce budworm larvae by the fungus Entomophaga aulicae
Authors: Murrin Faye , Nolan Richard A.
Published: September 2008

The infection of spruce budworm larvae by the fungus Entomophaga aulicae was studied by light, scanning, and transmission electron microscopy. Exposure of the larvae to conidia resulted in the death of the host and the production of a crop of infective conidia within 5 to 6 days. Germinating conidia produced appressoria prior to penetration of the larval cuticle. Nuclei in appressoria were larger and contained less heavily condensed chromatin than nuclei in other stages of fungal development. Attachment and infection were characterized by distinct changes in the wall layers of the fungus. An infection hypha grew through the insect tissues directly into the hemocoel where discontinuities were observed in the wall layers at the apex of the infection hypha. These discontinuities are probably associated with protoplast formation in vivo. Protoplasts with polysaccharide and lipid storage material were present in the hemolymph of larvae 3 days after exposure to conidia. Thick-walled hyphal bodies with abundant lipid reserve filled the larval body cavity by the 5th day. Hyphal bodies germinated to produce unbranched, aseptate conidiophores which emerged through the host cuticle prior to conidiogenesis.
Photoinhibition of net photosynthesis in Stereocaulon virgatum and S. tomentosum, a tropical–temperate comparison
Authors: Coxson Darwyn
Published: September 2008

Stereocaulon tomentosum Fr., collected in pine–lichen woodlands of southwestern Alberta, Canada, and S. virgatum Ach., collected from recent lahar flows on La Soufrière, Guadeloupe (French West Indies), were examined for their response of net photosynthesis and respiration to brief periods of high light exposure at temperatures ranging from 10 to 40 °C. In each species, a 30-min exposure period to photon flux densities of 1500 μmol∙m−2∙s−1 resulted in a significant reduction of subsequently measured rates of net photosynthetic CO2 uptake in those treatment groups which had been held at temperatures at or above 30 °C. These results suggest an altered stability of interactions between light and dark reactions of net photosynthesis at higher temperatures. They also point to the need for close monitoring of field microclimatic conditions during periods when hydrated lichen thalli are exposed to full sun conditions. Selective pressures imposed on hydrated lichen thalli during these periods of insolation shock may well prove of much greater importance in the shaping of net photosynthetic response patterns than has previously been recognized and may account for many of the previously observed disparities between those temperatures prevailing during typical periods of thallus hydration (i.e., under overcast conditions) and those at which maximal rates of net photosynthetic uptake are seen (often a full 10 to 15 °C higher). These interactions appear equally important to lichens of tropical origins and to those of north temperate habitats and suggest common evolutionary drives on thermal acclimation in both environments.
Population differentiation of the Stellaria longipes complex within Saskatchewan's Athabasca sand dunes
Authors: Macdonald S. Ellen , Chinnappa C. C. , Reid David M. , Purdy Brett G.
Published: September 2008

Stellaria arenicola, a recent derivative within the S. longipes complex, is an endemic of the Athabasca sand dunes. Analysis of 11 morphological characters on 40 genets showed that both the endemic and parental (S. longipes) species are present within the Thomson Bay dune field and that the two forms are distinct. Individuals of S. arenicola were distinguished by only a few characters, typically, large yellow capsules with reflexed teeth and yellowish leaf and stem pigmentation. The endemic also exhibited a higher sexual reproductive output. Many characteristics of vegetative morphology showed plasticity in both species, but the two remained distinct when grown in a common garden. On the sand dunes S. longipes is restricted to beach dunes bordering Lake Athabasca while S. arenicola is predominant on the active dune field inland. The two dune systems represented environmentally distinct microhabitats. The active inner dunes were characterized by an unstable, fine sand substrate and intense insolation. Field reciprocal transplants showed S. longipes was selected against in the inner dune habitat, while S. arenicola performed relatively well on the beach. Stellaria arenicola possibly arose in the active sand dune habitat as a result of selection pressure and genetic isolation.
Patterns of changes of dormant genotypes in Avena fatua populations under different agricultural conditions
Authors: Jana S. , Thai K. M.
Published: September 2008

Experimental evidence is provided to support earlier suggestions that summer-fallowing of cropland enhances the relative abundance of dormant wild oats at the expense of nondormant ones. Two heterogeneous populations of wild oats, Avena fatua L., were synthesized, each composed of a different set of true-breeding dormant and nondormant lines in equal initial frequencies. Subsequent generations of these mixed-stand populations were grown without conscious selection under two cultivation conditions: (i) propagation in every growing season (continuous cropping) and (ii) a 2-year rotation consisting of a year of propagation followed by a year of summer-fallowing. These experimental populations responded differently to the two cultivation practices. The relative frequency of dormant lines increased substantially in both populations propagated under the summer-fallow regime, compared with the continuous-cropping regime. Implications of this finding for weed control are discussed.
A new hand tool for cutting peat profiles
Authors: Wardenaar E. C. P.
Published: September 2008

A portable hand tool for cutting undisturbed profiles in peatlands has been developed and field tested. A column up to 1.7 m long, suitable for mounting, root investigations, or subsampling, can be obtained from different kinds of peatlands in less than 10 min.
Reaction of Hordeum species to the smut fungi Ustilago nuda and U. tritici
Authors: Nielsen J.
Published: September 2008

Eleven species of Hordeum were tested for their reaction to Ustilago nuda (Jens.) Rostr. and U. tritici (Pers.) Rostr., the causes of the embryo-infecting loose smuts of cultivated barley and wheat, respectively. The species Hordeum chilense and H. depressum were resistant, while H. euclaston, H. halophilum, H. procerum, H. pusillum, and H. stenostachys were susceptible to both fungi. Hordeum muticum was susceptible only to U. nuda, while H. arizonicum, H. lechleri, and H. roshevitzii were susceptible only to U. tritici. The susceptible species are new hosts for these pathogens. It is proposed that these results, together with those of an earlier study, indicate that U. nuda evolved from U. tritici.
The reproductive biology of boreal forest herbs. II. Phenology of flowering and fruiting
Authors: Helenurm Kaius , Barrett Spencer C. H.
Published: September 2008

The flowering and fruiting phenologies of 12 boreal forest herbs were recorded during 1979 (flowering and fruiting) and 1980 (flowering only) in spruce–fir forests of central New Brunswick. The species studied were Aralia nudicaulis, Chimaphila umbellata, Clintonia borealis, Cornus canadensis, Cypripedium acaule, Linnaea borealis, Maianthemum canadense, Medeola virginiana, Oxalis montana, Pyrola secunda, Trientalis borealis, and Trillium undulatum. Flowering in the community occurred from mid-May to the end of July. The order of flowering was maintained in the 2 years, but the degree of synchronization of inflorescences differed in several species. Fruiting in the community began in mid-July and extended beyond the end of September. The percentage of buds that ultimately bore fruit ranged from 0 (Cypripedium acaule) to 61% (Aralia nudicaulis). With the exception of Cypripedium acaule, which received little pollinator service, the self-incompatible species, Cornus canadensis, Maianthemum canadense, and Medeola virginiana, experienced the lowest levels of fruit-set. Pollen limitation and predation of developing fruit appear to be the major factors limiting percentage fruit-set in boreal forest herbs. Fruit production varied with time of flowering of inflorescences in several species, with periods of low fruit-set tending to coincide with lower densities of flowering inflorescences. Significant rates of fruit removal by herbivores occurred in all sarocochorous species. Disappearance of fruits from infructescences ranged from 31 (Medeola virginiana) to 95% (Aralia nudicaulis), with highest removal rates occurring during periods of greatest fruit availability.
Host–parasite relationships in dual cultures of Helianthus annuus and Plasmopara halstedii
Authors: Gray A. Bruce , Sackston W. E.
Published: September 2008

The downy mildew fungus (Plasmopara halstedii) sporulated on callus tissue of sunflower (Helianthus annuus) in dual cultures on tissue culture medium. The fungus was most concentrated in the seven outermost layers of the callus. No haustoria were found inside the host cells. Healthy callus from both susceptible and resistant sunflowers was successfully inoculated with pieces of the dual cultures, giving rise to mycelium but no spores on the fresh callus. Dual cultures developed at comparable rates in both the compatible and incompatible combinations; the downy mildew resistance of intact plants was not expressed in dual cultures under the environmental conditions used.
The relationship of tree height and crown class to the induced plant defenses of loblolly pine
Authors: Paine T. D. , Stephen F. M.
Published: September 2008

Loblolly pines, Pinus taeda L., were inoculated with a fungus associated with the southern pine beetle, Dendroctonus frontalis Zimm., at three heights to determine whether the trees responded to infection differently at each height. Loblolly pines responded to inoculation of this fungus by producing lesions of various dimensions. These were dissected and weighed. Lesions had the same weight at all three heights up the stem. However, the extent (or intensity) of reaction to fungal infection and wounding varied as a function of crown class of the tree. The influence of site quality on induced defenses may be assessed using this technique.
The pattern of vascular deployment near the pulvinus of the solar-tracking leaf of Lavatera cretica (Malvaceae)
Authors: Fisher F. J. F. , Ehret D. L. , Hollingdale J.
Published: September 2008

Distinguishable files of xylem and phloem elements that originate in first-order branches of the seven palmate major veins of Lavatera cretica leaves become separated from files unique to the radially aligned sections of the same veins before entering the pulvinus at the distal end of the petiole. The major veins initially merge to form a double coaxial tube: the outer cylinder comprises files unique to the major veins and the inner cylinder comprises files from lateral branches. Subsequent splitting, unfolding, and recombining of these cylinders results in the single narrow flexible tube constituting the hinge of the pulvinus. Proximal to this point, in L. cretica, the files reseparate into six alternately large and small petiolar bundles. The observed vascular pattern offers a means whereby signals from the lamina that elicit sun-tracking movements by the pulvinus can be integrated.
Regulation by carbohydrates of the sequential in vitro production of pectic enzymes by Botrytis cinerea
Authors: Leone G. , Heuvel J. Van den
Published: September 2008

Cultures of Botrytis cinerea in a basal salt medium supplemented with different pectin-related polysaccharides (French bean cell walls; citrus pectin; sodium polygalacturonate) as the only carbon source were examined daily for polygalacturonase activity, type of pectic enzymes present, and mycelial growth. Total polygalacturonase activity and number of enzymes detectable were influenced by type and concentration of the substrate and by the conidial concentration at which the cultures were started. A consistent sequence in the production of pectic enzymes was found. The polygalacturonase PG2 was always the first enzyme present in the culture filtrates and was followed by a number of polygalacturonase and pectinesterase isoenzymes. PG2 was also found in ungerminated conidia. Its production is the expression of a constitutive gene as it was independent of the presence of the substrate and strictly correlated with fungal growth. D-Galacturonic acid at 2 mM induced the production of some of the pectic enzymes. At 10 mM and above, however, it repressed PG2 and the subsequent production of the whole pectic isoenzyme complex, indicating a feedback repression. The results suggest that the pectic isoenzymes produced by B. cinerea constitute a coordinated catabolic pathway for the complete degradation of pectic polysaccharides.
The use of L-DOPA to enhance visualization of the "black line" between species of the Armillaria mellea complex
Authors: Hopkin A. A. , Mallett K. I. , Blenis P. V.
Published: September 2008

The zone of antagonism, known as the "black line," that occurred between the confronting margins of diploid isolates of different Armillaria mellea complex species was enhanced by incubation in L-β-3,4-dihydroxyphenylalanine (L-DOPA). Intraspecific crosses and crosses of genetically identical isolates did not produce a black line after similar treatment with L-DOPA.
Suppression of vesicular–arbuscular mycorrhizal fungus spore germination by nonsterile soil
Authors: Wilson G. W. T. , Hetrick B. A. Daniels , Kitt D. Gerschefske
Published: September 2008

When the effect of nonsterile soil on vesicular–arbuscular mycorrhizal fungus spore germination was examined, significantly fewer Glomus etunicatum (22 vs. 63 and 64%) or Glomus mosseae (23 vs. 80 and 79%) spores germinated in nonsterile soil than in autoclaved or pasteurized soil, respectively. In some cases, addition of nonsterile soil sievings to autoclaved or pasteurized soil also reduced germination, as compared with germination in unamended pasteurized or autoclaved soil. Germination was reduced by as much as 45% in autoclaved or pasteurized soil if spores were surface sterilized. However, surface sterilization of G. etunicatum spores did not affect dry weight of inoculated big bluestem plants, but mycorrhizal root colonization was reduced when spore-associated microbes were removed from spores by surface sterilization. The detrimental effect of soil microbes on spore germination and mycorrhizal growth response may reflect microbial competition for nutrients since germination of G. etunicatum and G. mosseae was reduced when pasteurized soil was amended with 15, 30, or 60 ppm phosphorus and 60 ppm phosphorus, respectively. An optimum range of available phosphorus may exist, above or below which germination is suppressed.
Pollination biology of Opuntia imbricata (Cactaceae) in southern Colorado
Authors: McFarland Jonnene D. , Kevan Peter G. , Lane Meredith A.
Published: September 2008

The floral phenology, compatibility system, and pollinator fauna of Opuntia imbricata (Haw.) DC. in southern Colorado were studied. The plants bloom for approximately 4 weeks in June and July. Opuntia imbricata sets numerous seeds when it is open-pollinated or experimentally cross-pollinated; it is self-incompatible and not apomictic. The most effective pollinators were found to be medium to large bees of the genera Diadasia and Lithurge; beetles are ubiquitous on flowers of O. imbricata, but probably do not effect pollination because they rarely move from flower to flower and usually restrict their activities to the stamens and base of the inside of the flowers.
Pure culture response of ectomycorrhizal fungi to imposed water stress
Authors: Coleman Mark D. , Bledsoe Caroline S. , Lopushinsky William
Published: September 2008

The ability of ectomycorrhizal fungal isolates to tolerate imposed water stress in pure culture was examined in 55 isolates of 18 species. Water potential treatments, adjusted with polyethylene glycol, were applied to Petri dish units. These units allowed colony diameter measurements of fungi grown on liquid media. Delayed growth initiation and inhibition of growth rate occurred with increasing water stress. For 87% of the isolates, growth rate was inhibited by the initial water potential treatment applied, leaving only seven isolates where growth increased with initial water potential treatments. No growth was evident under the imposed stress treatments for isolates of Laccaria bicolor, Laccaria laccata, and Lactarius controversus; growth occurred only in the control. Drought tolerant species, demonstrated by an ability to grow at a water potential of −3 MPa, included Boletus edulis, Cenococcum geophilum, Rhizopogon vinicolor, and five out of eight Suillus species. Species intolerant of −1 MPa included Hebeloma crustuliniforme, Laccaria bicolor, Laccaria laccata, and Suillus caerulescens. Fungal drought tolerance was poorly correlated with estimates of annual precipitation for collection locations. Estimates of drought tolerance seems to depend more on fungal classification than on annual precipitation at the site of collection. Reisolation of Laccaria bicolor increased growth rate and water stress tolerance when compared with the same fungus prior to reisolation.
Morphology of Treubiomyces pulcherrimus (Chaetothyriaceae)
Authors: Pohlad Bob R.
Published: September 2008

Treubiomyces pulcherrimus resembles Chaetothyrium, type of the family Chaetothyriaceae, in the following characters: a pale superficial mycelium appressed to the cuticle of living plants; a globoid ascoma developing beneath a mycelial shield, with which the ascoma is fused in the apical region; a centrum composed of a basal fascicle of aparaphysate asci; a palisade of short periphysoids projecting downward from the roof of the locule to the tips of the asci; and a schizogenous, periphysate ostiole. The asci have a conspicuous refractive ring in the thickened wall at the apex. Ascospores are discharged forcibly, but dehiscence of the presumed bitunicate asci could not be demonstrated. Mycelial cultures were obtained from ascospores discharged onto agar plates. No conidia were found in culture or field material.
Are Hordeum brachyantherum and H. californicum (Triticeae: Poaceae) conspecific?
Authors: Baum Bernard R. , Bailey L. Grant
Published: September 2008

Justifications for recognizing H. brachyantherum Nevski and H. californicum Covas as separate species are provided from multivariate morphometric analyses and from lodicule and epiblast characters. Although the range of variation of the latter species is included in the range of the former for most morphometric characters, the two are distinct when all of the characters are in multivariate space. Furthermore, H. brachyantherum is allotetraploid (2n = 4X = 28) and H. californicum is diploid (2n = 2X = 14) as previously reported. Identification to species can be done with a high degree of accuracy by means of the linear classification function coefficients, which after cross validation using the bootstrap method, has been found to be reliable, by the lodicules and epiblasts, or more conclusively by the chromosome number.
DNA synthesis and nuclease activity during germination of a heterotic F1 hybrid of maize
Authors: Mino Masanobu , Inoue Masayoshi
Published: September 2008

In maize, the DNA content and [3H]thymidine incorporation in embryonic cells and the nuclease activity in the fraction extracted from embryonic cells were determined in a heterotic F1 hybrid (Oh545 × W22) and its parental inbred lines. DNA content was higher in the F1 hybrid than in parental lines; however, [3H]thymidine incorporation was greater in W22 than in the F1 hybrid. Herring DNA splitting activity was higher in W22, and the yeast RNA hydrolyzing activity was almost the same in the F1 hybrid and W22. Oh545 had the lowest value in each of these parameters. It is suggested that qualitative and quantitative differences in DNA synthesis during the germination period between the F1 hybrid and the parental lines are related to the expression of heterotic vigor.