摘要:

Species composition, biomass and environmental characteristics of a coastal plant community of southeastern Brazil, was studied using data from 110 quadrats collected on the foredune of Barra de Maricá, Rio de Janeiro, Brazil. Indirect and direct gradient analyses were used to describe the foredune community. Ordination by detrended correspondence analysis (DCA) indicated the existence of three vegetation groups: pioneer, embryo dunes and a zone of fixed dunes with blow out areas. The gaps observed between groups were attributed to discontinuities in environmental factors. Most of the variation in species composition was expressed by the second axis of the DCA ordination, which was correlated with the distance from the beach bank. The second axis is interpreted as a stress gradient, with high stress in the pioneer zone decreasing to fixed dunes. The coenocline analyzed by direct gradient ordination, was divided into three segments equivalent to Groups detected by DCA ordination. The important species were:Althernanthera maritimaSt. Hil. in the pioneer zone, andSporobolus virginicus(L.) Kunth,Mariscus pedunculatus(R. Brown) T. Koyama, andMitracarpus frigidumK. Sch. in the embryo dunes.The grassPanicum racemosum(Spreng) was associated with areas of fixed dune. that were also characterized byMollugo verciticillataL. Both biomass and species richness were lower at the high stress disturbance ends of the gradient, with their maximum value in different portions of the middle range of the gradient.Key words: detrended correspondence analysis, direct gradient analysis, foredune communities, vegetation zonation

ISSN:0008-4026    

DOI:10.1139/b98-097

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A necrosis of succulent, elongating, current-year needles ofPinus strobusin the northeastern United States, frequently attributed to "ozone damage," is not due to ozone. The pathological anatomy of affected needles differs from that described for ozone injury and is virtually identical to that described as "semimature-tissue needle blight." The syndrome on affected trees throughout the northeastern United States is consistently associated with the presence of the needlecast fungus,Canavirgella banfieldii. This fungus occurs in the mesophyll of both healthy appearing and dying tissues of such needles before these needles have elongated to half their mature size. The pathological anatomy of infected needles agrees with that described for needlecasts by other researchers, beginning with R. Hartig. In contrast, healthy clones of field-symptomatic and field-asymptomatic trees exposed in open-top chambers to carbon-filtered air and to air adjusted on an hourly basis to 3× ambient ozone concentrations incurred a distinctly different tip necrosis. These necrotic tissues were delimited by an intercellular gummy deposit of unknown composition that appeared to be a type of walling-out response. No hyphae were present in these needles. The pathological anatomy of such needles resembled neither that of the symptomatic parent trees in the field, nor that previously demonstrated in various conifers as due to ozone.Key words:Pinus strobus,Canavirgella banfieldii, needle blight, needlecast, ozone

ISSN:0008-4026    

DOI:10.1139/b98-153

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Because of their unique phenology and physiology, spring ephemeral herbs are believed to play an important role in intrasystem nutrient cycling in deciduous forest ecosystems. It was hypothesized that they function as a "vernal dam" by temporarily sequestering nutrients and preventing leaching from the system during a period of high nutrient availability. However, spring ephemerals require high-irradiance growing conditions. How do their physiological and morphological responses to ambient light and shade limit their ability to sequester excess nutrients? We performed field experiments usingClaytonia virginicaL. as a model to test several responses to shade and increasing levels of nutrient additions. We also examined the biomass responses and nutrient storage capacities of other spring ephemeral herbs. InC. virginica, shading reduced ribulose 1,5-bisphosphate carboxylase-oxygenase (Rubisco) activity, photosynthesis rate, specific leaf weight, leaf width/length (W/L), and biomass; nutrient additions increasedW/Land biomass only under unshaded conditions. Other herbs responded similarly but reached maximum biomass at lower nutrient addition levels thanC. virginica. Shading reduced and nutrient additions increased nitrogen and phosphorus concentrations in bothC. virginicaand other herbs. Shaded herbs generally reached nutrient saturation at lower nutrient addition levels than unshaded herbs. Overall, unshaded plants sequestered larger amounts of nutrients than shaded plants. This pattern is best explained by a reduction in biomass under shaded conditions. We concluded thatC. virginicaand other spring herbs, although important components in forest nutrient cycling in the early spring, are limited in their capacity to store excess nutrients, particularly when shaded.Key words:Claytonia virginica, nutrient cycling, spring ephemerals, vernal dam.

ISSN:0008-4026    

DOI:10.1139/b98-134

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Single terminal inflorescences from two-stemmed plants ofRhododendronL. cv. 'Prize' and 'Gloria' were recurrently sampled during a 9°C cold treatment and subsequent forcing period in an 18°C growth chamber until plants reached anthesis. At each sample period, bud length and width were measured on each inflorescence, while subtending bud scale, petal, stamen ('Gloria' only), style, peduncle and ovary length, ovary width, and flower weight were determined on the two most basally attached flowers within an inflorescence for each cultivar. Polynomial regression models were calculated for each floral growth measurement over time, except for bud length and width, for each of the four flowers within a cultivar. Comparison of regression models revealed differences in floral part growth patterns among the various flowers within each cultivar. During the first week of placement in 18°C forcing temperatures after the cold treatment, bud length was the only floral part to grow on 'Prize' plants, while only female flower parts grew on 'Gloria' plants. These results indicate differences in growth resumption patterns between cultivars after cold storage. However, petal and style length were strongly correlated to flower weight for both cultivars indicating that these measurements could be used in laboratory or field situations to determine the floral stage of growth. The growth equations described would be useful for controlling the variability among shoots and flowers for analytical determinations, such as hormonal content analysis, and for studying relationships of floral growth patterns to environmental stimuli that could be used to control flowering. The statistical techniques used in this research make it possible to reduce the number of plants for such studies, as measurements taken on different flowers on the same plant can be used for floral part growth comparisons despite the inherent correlation present between such measurements.Key words: morphology, dormancy, growth modeling, multivariate multiple regression, controlled environme

ISSN:0008-4026    

DOI:10.1139/b98-100

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The quantity and quality of light have significant effects on tree growth and architecture that can be highly variable depending on the shade tolerance of the species. A study was conducted to determine the effect of decreased availability of photosynthetically active radiation (PAR) on the growth and architecture of green ash (Fraxinus pennsylvanicavar.subintegerrima(Vahl) Fern.), a moderately shade-tolerant species. Twenty-four seedlings were planted in each of five shade treatments (4, 8, 20, 40, and 100% of full sun, respectively). Measurements made over a 2-year period revealed that with decreased PAR levels there was generally a reduction in leaf thickness, number of shoot units per shoot, shoot-unit length, shoot growth, branching frequency, lateral shoot growth, and shoot biomass. However, in moderate reductions of PAR, there were increases in shoot unit numbers, overall shoot length, and branch numbers. The overall effect of heavy shading was to produce a tree with little height growth and a poorly developed crown.Key words:Fraxinus, shading, seedling morphology, shoot unit, light quantity, architecture.

ISSN:0008-4026    

DOI:10.1139/b98-126

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Terpene concentration and emission were studied in potted plants of some of the most common Mediterranean woody species (Pinus halepensisL.,Pistacia lentiscusL.,Cistus albidusL.,Cistus monspeliensisL.,Quercus ilexL.,Quercus cocciferaL.,Phillyrea latifoliaL.,Phillyrea angustifoliaL., andArbutus unedoL.) under irrigation and under severe drought conditions that dropped relative water content to a range between 40% inQ. ilexand 85% inPhillyrea latifoliaafter withholding watering for one dry summer week. Terpene concentrations were detected inPinus halepensis,Pistacia lentiscus,C. albidus, andC. monspeliensis, and they increased after withholding watering except inC. albidus. Terpene emission was detected in all species exceptPhillyrea angustifoliaandA. unedo.Pinus halepensisshowed the highest diurnal terpene emission rates of 86 µg·g-1dry wt.·h-1followed byC. albidus,Pistacia lentiscus,Q. ilex,Q. coccifera,Phillyrea latifolia, andC. monspeliensis(4 µg·g-1dry wt.·h-1). Emitted terpenes represented from 0.33% of C fixed inC. monspeliensisto 10% inC. albidus. All species severely decreased their terpene emission rates under severe drought conditions. Emission by terpene-storing species (e.g.,Pinus halepensis) was more related to temperature than in nonstoring species (e.g.,Q. ilex), which showed emission relationships with photosynthetic rates. The monoterpenes alpha-pinene, beta-pinene, beta-phellandrene, and limonene and the sesquiterpene caryophyllene were the most abundant terpenes stored and emitted by these Mediterranean plant species.Key words: drought, Mediterranean conditions, terpene concentration, terpene emission, woody plant

ISSN:0008-4026    

DOI:10.1139/b98-141

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Lipara lucensMeigen (Diptera, Chloropidae) is a monophagous herbivore of the common reed,Phragmites australisCav. (Trin.) ex Steud. (Poaceae), on which it induces typical cigar-shaped galls. In this paper, the anatomy and histochemistry of galls, cultivated in a greenhouse and collected in the field, were examined. Gall growth takes place while the larva feeds outside the actual developing gall. During gall growth, internode elongation is reduced. Internally, the pith parenchyma, destined to become the nutritive tissue, proliferates instead of degenerating as is seen in uninfested stems. The tissue cylinder around the gall chamber widens up to three times its normal size, while the pith parenchyma doubles its width. The central pith of nutritive cells becomes surrounded by an inner layer of longitudinal and an outer layer of radial parenchymatous cells. Vascular strands, likely connected to the vascular tissue of the host plant, run through this special band of parenchyma cells. The bundles are oriented perpendicular to the stem axis, surrounding the larval chamber. When the gall is completed, the larva gnaws through the growing point and enters the gall chamber, where it consumes the nutritive tissue. A sclerenchymatization process starts now resulting in an extremely hardened gall. Histochemical staining reveals the presence of proteins, DNA, RNA, and a gradient of lipid globules in the nutritive tissue. No starch was detected.Key words: plant-insect interactions,Lipara lucens,Phragmites australis, gall structure.

ISSN:0008-4026    

DOI:10.1139/b98-143

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

In grapevines, the young leaves play an important role in the control of the growth of anticipated buds. Through a basipetal inhibition, which these young leaves exercise over subjacent buds, they contribute to apical dominance. This inhibitory influence persists as long as the duration of laminar growth of the leaf; it is neither sector-based nor cumulative; it is perceived even by buds very far from young leaves. This foliar inhibition is also one of the causes of the acrotonic character of lateral ramification that develops, in the apical part of the shoot, after shoot tip removal. In the older part of the shoot, this acrotony, consecutive to a shoot section, is mainly determined by correlations between the buds. All these results are analysed and discussed in regard to morphogenesis elements previously established in other species. The contribution of young leaves to apical dominance has been demonstrated previously in many other plants. On the other hand, in grapevine, this morphogenetic character was unknown. The fact that young leaves contribute to the acrotonic development of the lateral ramifications growing after decapitation of the main shoot constitutes a much more original result because it has rarely been described in previous studies relative to other species. Earlier works also lead us to expect that both correlative inhibitions and competitive process are involved in the correlations between anticipated buds released from apical dominance. Concerning the growth correlations between grapevine buds, only thuse correlations relative to latent buds had been, until now, very much studied. New and precise knowledge on correlations that control the development of anticipated buds are supplied by this work. It appears then that correlations between these two sorts of buds have two common features: inhibition of their growth by young leaves and sectorial character of the inhibitions between the buds. A hypothesis on the mechanisms through which young leaves control the growth of anticipated buds is suggested. These mechanisms probably change in relation with the developmental stage of a bud; before the bud develops, the young leaves exercise on it a basipetal polarized inhibition. As soon as the bud begins to grow, nonpolarized competitive relations become established between the lateral ramification and the upper young leaves.Key words:Vitis vinifera, apical dominance, acrotony, leaves, buds, correlations.

ISSN:0008-4026    

DOI:10.1139/b98-051

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Flowering pattern, seed-set success, and allocation to male and female functions of a spring ephemeral lily,Gagea lutea, were compared within individual inflorescences. Although the number of flowers increased with plant size and anthesis was extended as the number of flowers increased from one to four, the total number of seeds produced per plant did not increase with the number of flowers under natural conditions. The later-blooming flowers were smaller in size than the earlier ones within an inflorescence, and the ratio of stamen dry weight to pistil dry weight in the later flowers was higher than that in the earlier ones. Although the ovule fertilization rate was increased by artificial pollination, it was lower in the later flowers than in the earlier ones within an inflorescence. Neither nutrient addition to the soil nor removal of earlier flowers increased the seed production of the later flowers. These results indicated that the later flowers had a lower potential for female function than did the earlier ones and that this was probably due to variation inherent in inflorescence architecture. Seed production of the later flowers was also limited by the time needed for seed maturation because the aboveground part ofG. luteadied soon after canopy closure in early summer. Furthermore, the later flowers probably contributed to the reproductive success of a plant as pollen donors.Key words: flowering order,Gagea lutea, resource allocation, seed production, short growing season.

ISSN:0008-4026    

DOI:10.1139/b98-120

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Sphaeropsis sapinea(Fr.) Dyko & Sutton is an opportunistic pathogen of variousPinusspp., causing severe shoot blight and dieback. Some isolates ofS. sapineadisplay characteristics such as reduced virulence, reduced growth rate, lack of pigmentation, altered colony morphology, and suppressed conidiation. South African isolates ofS. sapineadisplaying a range of growth patterns, including reduced growth rate and atypical morphology, were screened for the presence of double-stranded RNA (dsRNA). They were also tested for relative virulence in pathogenicity tests. Double-stranded RNA was isolated by means of phenol extraction and cellulose chromatographic purification. A single species of dsRNA (± 4.3 kilobase pairs in size) was obtained from two slow-growing isolates and two isolates with more regular growth. The virulence of these dsRNA-containing isolates was tested on maturePinus patulaSchlecht. et Cham. trees. Although reduced virulence was positively correlated with slower growth in vitro, the presence of dsRNA could not be linked to either of these characteristics.Key words: double-stranded RNA, hypovirulence,Sphaeropsis sapinea.

ISSN:0008-4026    

DOI:10.1139/b98-113

出版商:NRC Research Press    

年代:1998

数据来源: NRC