摘要:

The thermal acclimations of net photosynthesis, dark respiration, and photorespiration have been studied in the arctic plantSaxifraga cernua. The gas exchange of whole plants grown to maturity under different temperature regimes was analysed for individual plants transferred from (i) 10 to 20 (referred to as high-temperature acclimation) and (ii) 20 to 5 °C (low-temperature acclimation). High- and low-temperature acclimation resulted in shifts of the leaf temperature optimum for net photosynthesis of whole plants in the direction of the new growth temperature. That the acclimating temperature directly affected the photosynthetic apparatus was indicated by (i) changes in the optimum temperature for gross photosynthesis of whole plants and (ii) a change in the oxygen sensitivity of net photosynthesis after acclimation to a new growth temperature. The change in the optimum temperature for net photosynthesis was also due, in part, to altered dark respiration rates which increased during acclimation to low growth temperatures. These results suggest that such acclimation in arctic species likeS.cernuaarose as a result of the selective pressure of fluctuating temperatures which are experienced during the growth season to maximize annual growth under arctic and subarctic conditions.

ISSN:0008-4026    

DOI:10.1139/b86-011

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The vegetation sequence on granitic outcrops containingOpuntia fragilis(Nutt.) Haw. was examined at three sites in southeastern Manitoba. The experimentally determined species sequence supported those in the literature: (0) bare rock – pioneer lichens, (1) primary moss mat, (2) secondary moss and lichen mat, (3) tertiary moss and lichen mat, (4) stress-tolerant ruderals, (5) stress-tolerant perennials, (6) perennial grasses, and (7) chamaephytes and phanerophytes. The primary factor determining the sequence was substrate depth, presumably because of its effect on moisture retention. The species composition of the earliest seral stages (0–3) was consistent at all three sites, presumably as a result of propagule availability and the extremely xeric nature of the sere. Variations in the species of subsequent stages may be attributed to the more restrictive dispersal mechanisms of mesic species. Local variations in vegetation scale and pattern were caused by slope, disturbance, crevices or depressions, and encroachment of forest at the forest–outcrop ecotone.Opuntia fragilis, a stress-tolerant perennial, was the first vascular plant in the sequence and colonized mats in stage 2 (occasionally 3). It did not persist in stage 5.

ISSN:0008-4026    

DOI:10.1139/b86-012

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Thin sections of malva (Malvasp.) leaves collected in the field and showing mottle and vein-clearing symptoms were examined by electron microscopy. Cytoplasmic inclusions typical of potyvirus and consisting of pinwheels, laminated aggregates, and scrolls were readily observed. In addition, rhabdoviruslike particles were also seen in the perinuclear space of phloem parenchyma cells and within membranous sacs scattered throughout the cytoplasm of other vascular bundle cells. Occasionally rhabdoparticles could be found embedded in an amorphous electron-dense body located within the cell vacuole. The rhabdovirus particles, approximately 75 × 300 nm, were bound by a membrane with outer projections and had an inner core displaying cross striations. The cytoplasm of infected mesophyll cells had chloroplasts containing large amorphous inclusion bodies and had extensive membranous tubules that were frequently associated with the potyvirus inclusions. These ultrastructural aspects, the size of the particles, and the data on host range indicate that malva plants under study were doubly infected by viruses which were tentatively identified as malva vein-clearing virus and a previously undescribed rhabdovirus.

ISSN:0008-4026    

DOI:10.1139/b86-013

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

A new species of endogonaceous fungus mycorrhizal with barley in Alberta is described.Glomus dimorphicumsp. nov. has two types of spores formed singly and in loose, often radiately arranged clusters. This new species produces very few vesicles, and arbuscule formation has so far not been observed.

ISSN:0008-4026    

DOI:10.1139/b86-014

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The cell wall ultrastructure ofGracilaria verrucosawas investigated, using electron microscopy, before and after extraction of the agar by two techniques. In this species, the agar is the main constituent of the cell wall matrix. The amorphous part of the cell wall disappeared after extraction and some structural modifications of the fibrillar squeletic phase were observed. These observations showed that a mild extraction method improves the colloid purity.

ISSN:0008-4026    

DOI:10.1139/b86-015

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Colonization ofAbies albaMill, needles byLophodermium piceae(Fckl.) Höhn. (Ascomycetes, Hypodermataceae) was studied by light and electron microscopy. Internal mycelium is at first extracellular and invades all the tissues of the needle; thereafter hyphae may penetrate all cells. Cytoplasm and walls of living cells (parenchyma, phloem, cellulosic transfusion tissues) are then lysed. Hyphae also invade thick-walled and lignified cells (epidermis, hypodermis, xylem, tracheids, and fibers of transfusion tissues) without major degradation of the cell wall. Ascomatal development is intraepidermic. Colonization of the needles is limited by black areas (the diaphragms), the structure of which is described.Lophodermium piceaeis a primary saprophyte. Needles are colonized during senescence but ascomata appear only on fallen needles. There are about 230 ascomata per gram of needles. The ecology of this fungus is compared with that ofThysanophora penicillioides(Roum.) Kendrick onAbiesneedles and with that ofLophodermium pinastri(Schrad.) Chev. onPinusneedles.

ISSN:0008-4026    

DOI:10.1139/b86-016

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Female gametophytes ofPicea abieswere collected during their growth period (June and July). Tissues were prepared for light microscope examination of their development and for protoplast isolation and further DNA measurements. From archegonia initiation to early embryo development, protoplasts could easily be obtained from such gametophytes. Stained and fixed nuclei, prepared from the protoplasts, were subjected to flow cytometry and their DNA content was recorded to be half that of seedling derived nuclei.

ISSN:0008-4026    

DOI:10.1139/b86-017

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Ceratocystis montia(Rumb.) Hunt, an ascomycetous fungus, is associated with bark beetle infested lodgepole pine in the intermountain region of United States and portions of western Canada. The organism, when inoculated into lodgepole pine (20 years old) caused necrosis of the inner bark, a blue-stained appearance of the sapwood, and chlorosis and necrosis of the foliage. Koch's postulates were fulfilled in these experiments. Particles of inner bark provided the best support for fungal growth and inhibitors of fungal growth may develop in sapwood during the process of drying.

ISSN:0008-4026    

DOI:10.1139/b86-018

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Gibberella fujikuroi(anamorphFusarium moniliforme) mating group A isolates from corn and sorghum were categorized into different vegetative compatibility groups, usingnitmutants (mutants unable to reduce nitrate or chlorate) to observe heterokaryosis among the compatible isolates. Vegetative incompatibility seems to be widespread in nature in this fungus and is controlled by nuclear genes calledhetorvicgenes. A total of ninehetgenes were estimated forG.fujikuroimating group A. Based on the independent segregation of ninehetgenes, 512 vegetative compatibility groups may be present in nature. However, only 13 vegetative compatibility groups were identified among conidial isolates recovered from Nebraska. The frequency of individual vegetative compatibility groups in a disease complex may be useful for monitoring pathogenicity genes in this fungus.

ISSN:0008-4026    

DOI:10.1139/b86-019

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Even-aged aspen (Populus tremuloidesMichx.) stands in regions with contrasting climates differ from one another in the growth rates of individual stems and in the rates at which they self-thin. The dependence on stand age of four statistics describing stand structure (the mean, standard deviation, and skewness of the distribution of tree girths and the number of trees in a 400-m2plot) were studied in three geographical regions: northern Alberta, Yukon, and the Foothills of the Rocky Mountains in southern Alberta. Each region has unique stand statistics. The annual radial increment is least in the Yukon, presumably because of the short growing season. Foothills plots are unique in having girth distributions that are approximately symmetrical at all ages; this contrasts with the other two regions, where girth distributions exhibited positive skewness in young stands and skewness decreased with age. Also in Foothills plots, the standard deviations of the girths increased more slowly with age than in the other two regions. A model was devised to simulate the progressive changes in these statistics in a stand as it ages. To run the model, one begins with data from an actual, observed stand for which the distribution of the trees in different size classes is known. It is then assumed that the trees grow; the growth rate of a tree is greater the larger the tree was initially. Simultaneously, trees die; the probability that a tree will die is greater the smaller the tree was initially. Thus, the values that the descriptive statistics of a given young stand are expected (according to the model) to have when the stand is old can be predicted; the predictions can be compared with current statistics of observed stands that are already old.

ISSN:0008-4026    

DOI:10.1139/b86-020

出版商:NRC Research Press    

年代:1986

数据来源: NRC