摘要:

Tomato (Lycopersicon esculentumMill.) plants were exposed, in controlled environments with 2.7 kJ/(m2 ∙ day) background ultraviolet-B (UV-B) radiation from fluorescent and incandescent lamps, to ambient (380 μL ∙ L−1) or elevated (600 μL−1) CO2combined with a total of 7.2 or 13.1 kJ/(m2 ∙ day) UV-B radiation to determine effects on growth and photosynthesis. Ten consecutive days of exposure to the higher level of UV-B significantly reduced total and stem dry weight, leaf area, and plant height compared with the lower level. Only leaf area and plant height were significantly reduced after 19 consecutive days of exposure. To investigate whether plants recover from UV-B damage, the UV-B exposures were halted for 3 days after 19 days of UV-B exposure and then restarted for a further 2 days. The largest reduction in plant growth was found after 3 days with no UV-B followed by 2 days of the higher level of UV-B. Plants did not recover from UV-B damage during the 3 days with background UV-B. Significant CO2xUV-B interactions were detected on stem dry weight after 10 consecutive days of the higher level of UV-B and on total dry weight, leaf dry weight, stem dry weight, and plant height after 3 days with no UV-B followed by 2 days of the higher level of UV-B. The higher dose of enhanced UV-B resulted in more severe damage at 600 μL ∙ L−1CO2, than at ambient CO2. The higher level of UV-B did not affect the leaf net photosynthesis rate on a leaf area basis, although this UV-B level may have inhibited tomato growth through reducing the photosynthetic area. UV-absorbing compounds in leaves in the highest UV-B radiation level for 19 days were greater than for leaves with the lower dose. These UV-absorbing compounds in the higher UV-B dose diminished more than in the lower dose plants during the 3 days without UV-B. The UV-absorbing compounds maintained by plants exposed to the highest level of UV-B radiation may have protected plants from UV-B damage, particularly between 10 and 19 consecutive days of exposure.Key words: CO2, growth,Lycopersicon esculentumMill., photosynthesis, tomato, ultraviolet-B radiation (UV-B), UV-absorbing co

ISSN:0008-4026    

DOI:10.1139/b97-022

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The first documented records ofPorodisculus pendulusin Canada are from southern Ontario and southwestern Quebec. The cultural characters of the fungus are described for the first time. The numerous and sometimes improper names applied to this fungus are detailed and discussed, and type specimens are indicated for the epithets. Allied species are discussed. The global distribution of the fungus, which includes Africa, Asia, Australasia, and the Americas, is expanded.Key words: Basidiomycetes, systematics,Porodisculus, biogeography.

ISSN:0008-4026    

DOI:10.1139/b97-023

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

In hermaphroditic higher plants, reproductive fitness can be achieved through male and female functions. The relative allocations to reproduction by maternal and paternal investments define the gender of each individual. In wind-pollinated species, the theory predicts that gender should evolve with plant size, the largest plants investing the most in male function. More specifically, the tallest plants should exhibit the highest degree of maleness, because pollen dispersal is most effective when the release point is high. We searched for potential variation in gender with plant size in pearl millet (Pennisetum typhoides), where each plant produces several shoots. Size was estimated by using four parameters, namely height, stem diameter, total leaf area, and vegetative weight, for shoots and for plants. Gender was estimated as the pollen to ovule (P:O) ratio for each shoot or plant. We found that allocation to male function is very variable, both between shoots within a plant and between plants. Most of the difference observed is correlated with differences in the weight of the shoots or plants, the heaviest ones having the highest P:O ratios. The theoretical prediction that maleness should increase with plant height was not fulfilled. The parameter used to estimate plant size seems to have a great influence on the ability to detect gender variation with size. The allocation to reproduction (defined as the weight of seeds, stamens, floral parts, and rachis of the spike) represented a decreasing proportion of total plant weight; also, the heavier the plant, the higher the proportion of this allocation devoted to male function. Since pearl millet is a cultivated species, this may be due to the fact that the domestication process, by selecting for larger plants, involuntarily selected for maleness by favoring the largest plants.Key words: pearl millet, resource allocation, sexual function, plant size.

ISSN:0008-4026    

DOI:10.1139/b97-024

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Allelopathy and endophytic fungi were evaluated as factors affecting the biological control of marsh reed grass,Calamagrostis canadensis(Michx.) Beauv., a weed of boreal reforestation areas. Leachate from marsh reed grass straw inhibited root growth into liquid and agar media and increased foliar necrosis. Most seedlings harboring endophytic species ofFusariumandChaetomiumwere healthy in agar controls, but all such seedlings were diseased when grown in agar with straw leachate. The straw leachate and various fungi had distinct impacts on the virulence ofColletotrichumsp., a potential biocontrol agent for marsh reed grass. In comparisons of control and allelopathic media,Colletotrichumsp. stimulated the overall vigor of reed grass while reducing vigor in the allelopathic medium. Individual isolates of fungi in the generaEpicoccum,Drechslera, andFusariumwere uniformly antagonistic toColletotrichum, whereas antagonism in individual isolates ofChaetomium,Alternaria, andStemphyliumdepended on the presence or absence of allelopathy. AnotherFusariumisolate increased the virulence ofColletotrichumsp. in both media, as did two applications ofColletotrichumsp. Allelopathic compounds,Fusariumsp., andColletotrichumsp. are potential components of a strategy for biological control of marsh reed grass.Key words: weed, biological control, bioherbicide, mycoherbicide.

ISSN:0008-4026    

DOI:10.1139/b97-025

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Rights-of-way are kept free of tall trees to insure reliability of electric service. Selective management techniques such as application of cut-stump herbicide and stem foliar herbicide are used on some rights-of-way to remove undesirable tree species while minimizing disturbance to shrub and herbaceous vegetation. Because rights-of-way typically traverse broad productivity and disturbance gradients over large geographic areas and harbor both native and non-native species, they offer unique opportunities to study plant species diversity patterns and their underlying causes at different scales. Plant cover on six managed rights-of-way in forested landscapes of New York State was sampled to determine the effect of landscape position (i.e., xeric, mesic, and hydric sites) on species composition, diversity, and richness and contribution of non-native species. Species composition among sites was compared using redundancy analysis in which the individual covers of the most common species were ordinated with treatment levels. Diversity, species richness, and contribution of non-native species were compared using analysis of variance. Redundancy analysis shows trends in the occurrence of common species based on landscape position. Analysis of variance indicates diversity, richness, and contribution of non-natives are greater on the rights-of-way versus the adjacent woods for xeric and mesic positions, whereas no differences were indicated between rights-of-way and adjacent woods for hydric positions.Key words: rights-of-way, selective management, diversity, competition, stress, invasive species.

ISSN:0008-4026    

DOI:10.1139/b97-026

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Transmission electron microscopy of plunge-frozen and freeze-substituted samples was used to examine germinating conidia ofAlternaria cassiae, a plant pathogenic fungus used as a biological control agent for sicklepod (Cassia obtusifolia). Hydrated conidia on small pieces of dialysis membrane were incubated for 1, 2, or 3 h on the surface of corn meal agar prior to fixation. Conidia were large, darkly pigmented, and surrounded by a thick, two-layered wall. Each conidium was divided by transverse and longitudinal septa into multiple cells, a few of which sometimes appeared necrotic. Each septum tapered to a small central pore region with which Woronin bodies were associated. Each healthy cell of a conidium contained a typical complement of cellular organelles including multiple nuclei. With the exception of lipid bodies, all the various organelles were well preserved by plunge freezing and freeze substitution. Evidence of germ tube development was visible by 2 h post-incubation and well-developed germ tubes were present by 3 h. Two modes of germ tube development were observed. In the less common mode germ tubes developed inside conidia and grew internally through one or more adjacent cells before emerging from the conidium surface. Cells penetrated by internal germ tubes appeared necrotic. In the more common mode of germination, germ tubes developed directly from the conidium surface. Multiple germ tubes usually arose from each conidium and grew out in all directions. Germ tubes that contacted the underlying dialysis membrane continued to grow along its surface. Extracellular material was produced in association with developing germ tubes and coated the sides of germinated conidia and covered germ tubes growing along membranes.Key words: transmission electron microscopy, cryofixation, freeze substitution, germ tube development.

ISSN:0008-4026    

DOI:10.1139/b97-027

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Habitat data, although sparse, and occurrence are summarized for nine rare or uncommon species ofAlbatrellus. Significant range extensions areAlbatrellus avellaneusin British Columbia, Oregon, and Washington,Albatrellus caeruleoporusin California, British Columbia, Oregon, and Washington,Albatrellus dispansusin Washington,Albatrellus ellisiiin Colorado, Oregon, Washington, and Wyoming,Albatrellus flettiiin Alaska, Alberta, northern British Columbia, Idaho, New Mexico, and Wyoming,Albatrellus subrubescensin Alberta, California, Northwest Territories, and Washington,Albatrellus syringaein North America (Alaska, Alberta, British Columbia, and Yukon Territory). Three additional collections ofAlbatrellus skamaniusbring the total known collections of the species to four; all are from the same general locality. A key to the western species, emphasizing features of fresh basidiomes, is included. The basidiome features of these species are supplemented with data from additional collections. Spore sizes in several species are more critically defined. Amyloidity occurred in basidiospores and (or) hyphaeof A.avellaneus,Albatrellusaffin.cristatus,A.ellisii,A.flettii,A.skamanius, andA.subrubescens.Key words: systematics, ecology, Basidiomycetes, conservation, biodiversity, fungi.

ISSN:0008-4026    

DOI:10.1139/b97-028

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Mass spectrometric measurements of16O2,18O2, and13CO2were used to measure the rates of gross O2evolution, O2uptake, and CO2assimilation in relation to light intensity, temperature, pH, and O2concentration by air-grown cells of the cyanobacteriumSynechococcusUTEX 625. CO2fixation and O2photoreduction increased with increased light intensity and, although CO2fixation was saturated at 250 μmol ∙ m−2 ∙ s−1, O2photoreduction was not saturated until about 550 μmol ∙ m−2 ∙ s−1. At high light intensity addition of inorganic carbon to the cells stimulated O2photoreduction 2-fold when CO2, fixation was allowed and 5-fold when CO2, fixation was inhibited with iodoacetamide. The ability of O2, to act as an acceptor of photosynthetically generated reducing power was dependent upon the O2concentration, and the substrate concentration required for half maximum rate (K½(O2)) was 53.2 ± 4.2 μM (mean ± SD,n = 3). The Q10for oxygen photoreduction was about 2. A certain amount (10%) of O2appeared to be required for maximum photosynthesis, as photosynthesis was inhibited under anaerobic conditions, especially at high light intensity. The point of inhibition is unknown but it seemed unlikely to be on CO2transport or the concentration of intracellular dissolved inorganic carbon (Ci), as the rate of initial CO2transport was enhanced and the intracellular Q1pool increased in size under anaerobic conditions.Key words: cyanobacteria, photosynthesis, Ciconcentrating mechanism, inorganic carbon pool, O2photoreduction, electron transport, temp

ISSN:0008-4026    

DOI:10.1139/b97-029

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The foliose lichenUmbilicaria americanaPoelt & Nash was exposed to spectrally altered radiation in three growth chamber experiments and one field experiment. After 1 week in growth chambers the phenolic content (% w/w) increased significantly under a spectral band including visible light and UV-A, and the increase was greater when intensity was higher. Under exposure to both UV-A and UV-B the concentration of phenolics was lower than with UV-A alone and, depending on dosage, approached or achieved control levels. In a population ofU.americanaon a vertical rock face, the interaction between filter treatments and collection dates had a highly significant effect on phenolic levels (P = 0.01). In thalli protected from UV-B, phenolic levels were higher than in those exposed to natural sunlight in June and October, but the same response was not observed in July and August. Thallus groupings covered by filters that admitted both UV-B and UV-A accumulated less phenolics than controls in August, but on other sampling dates contained the same concentrations.Key words:Umbilicaria americana, UV-A, UV-B, depsides, tridepsides.

ISSN:0008-4026    

DOI:10.1139/b97-030

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Cyanobacterial cells ofSynechococcusUTEX 625 were suspended in increasing extracellular inorganic carbon (Ci, up to 1 mM) under steady state photosynthesis conditions in a cuvette connected to a mass spectrometer. Photosynthetic CO2fixation, net CO2, and net HCO3−transport increased with increased extracellular Ciup to 100 μM [C1], with HCO3−transport contributing the most to the maintenance of the internal Cipool. When the extracellular [Ci] was increased above 100 μM, CO2, fixation and net CO2transport increased toward their maximum rates but net HCO3−transport progressively declined. At an extracellular [Ci] of 1 mM, the net HCO3−transport rate was only 15% of its value at 100 μM extracellular [Ci]. Under steady state photosynthesis conditions, the gross HCO3−transport rate remained at its maximum value at extracellular [Ci] above 100 μM either when CO2transport was precluded (i.e., in the presence of 200 μM Na2S) or when HCO3−transport was measured with H14CO3−and silicone oil filtration. As HCO3−efflux, calculated using the permeability coefficient determined at low [Ci], could not account fully for the decrease of the net HCO3−transport rate, Ciefflux and CO2, efflux were measured at high extracellular [Ci] during the initial period of darkness. With increasing intracellular [Ci] Ciefflux over intracellular [Ci] increased linearly but CO2, efflux over intracellular [Ci] was constant, hence the HCO3−efflux obtained by the difference between the Ciand the CO2efflux increased hyperbolically. Using HCO3−and CO2, efflux, we calculated that the permeability coefficient of the cell envelope for HCO3−but not for CO2increased with increasing intracellular [Ci]. When the HCO3−efflux was measured under steady state Ciflux conditions in the light, the permeability coefficient of the cell envelope for HCO3−also increased with increasing intracellular [Ci]. Reasons for the change in whole cell permeability to HCO3−at high extracellular [Ci] are discussed.Key words:SynechococcusUTEX 625, blue green algae, cyanobacteria, active HCO3−transport, HCO3−leakage, Ciconcentrating mechanism.

ISSN:0008-4026    

DOI:10.1139/b97-031

出版商:NRC Research Press    

年代:1997

数据来源: NRC