摘要:

The impact of mycorrhizal symbiosis on growth ofAndropogon gerardii(big bluestem) andKoeleria pyranidata(junegrass) was compared.Andropogon gerardiiwas 98% dependent on the symbiosis, whereasK.pyranidatadisplayed less than 0.02% dependence. Mycorrhizal fungus inoculation resulted in 50 times largerA.gerardiiplants but did not alter growth ofK.pyranidata. When competing in pairs,A.gerardiidominated when the mycorrhizal symbiosis was present andK.pyranidatadominated when it was not present. Dry weight of mycorrhizalA.gerardiiwas altered, whether grown alone or withK.pyranidata, but mycorrhizalK.pyranidatagrew well only in the absence of competition and failed to grow appreciably ifA.gerardiiwas present. Without mycorrhizal fungus inoculation,A.gerardiidid not grow and had no deleterious effects onK.pyranidata. When P fertilization was substituted for mycorrhizal fungus inoculation,A.gerardiigrew better alone than in competition withK.pyranidataat low P levels but was not affected by competition at high P levels.Koeleria pyranidatawas not affected by competition at low P levels, but high P fertilization resulted in reduced dry weight ofK.pyranidataplants when in competition withA.gerardii. Phenologic separation of growing seasons avoids interspecific competition between these two grasses and may be one mechanism contributing toward their coexistence. Since low temperatures limit mycorrhizal nutrient uptake, phenologic separation of growing seasons could also avoid the competitive advantage of warm-season grasses conferred by their mycorrhizal dependence.

ISSN:0008-4026    

DOI:10.1139/b89-337

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Total macro fungus frequency in closed forest associations of the Laurentide Mountains varied little (147 – 185 %) from one to another. The macrofungal flora of the deciduous forest was composed mainly of many infrequent species, whereas coniferous forests had few, but very frequent, macrofungi. Total frequency was significantly lower (15%) in open stands of the spruce–cladina association. Species richness decreased gradually (from 125 to 34 species) towards the north and with increasing altitude. Both the Simpson and the Shannon–Wiener diversity indices were significantly lower in the coniferous forest when compared with the deciduous forest. This decrease in diversity was due to the scarcity of saprophytic fungi in mor humus, whereas the number of ectomycorrhizal species remained constant. The diversity of saprophytic fungi was related significantly to that of vascular plants, whereas the diversity of ectomycorrhizal macrofungi was related mainly to the percent cover of ectomycorrhizal hosts. A total of 195 species of macrofungi were recorded for the study sites. In the maple – yellow birch forest, most of the macrofungi were saprophytic members of theTricholomataceae,Hygrophoraceae,Strophariaceae, andClavariaceae, many being exclusive in this association. However, each biological group had approximately equal frequency (44–54%) and richness (37–45 taxa). Species composition of the coniferous forest differed from the former in the clear dominance of ectomycorrhizal macrofungi from theCortinariaceae,Russulaceae, and theBoletaceae. In the black spruce – cladina association, saprophytic fungi were scarce and ectomycorrhizal species were also relatively infrequent. In all the sites, the equitability of macrofungal frequency was high, as seen by the high proportion of rare species. The decline in species richness observed in this study, when moving from deciduous to coniferous forests, corresponds well with the increase in environmental rigor and instability, as well as the decrease in the diversity of organic substrate and species of vascular plants.

ISSN:0008-4026    

DOI:10.1139/b89-338

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The spatial pattern of 1375 jack pine individuals (459 live, 257 standing dead, and 659 stumps) in a pure, even-aged, naturally established stand was mapped. Three maps corresponding to different stages of stand development were recognized: live + dead (initial pattern,n = 1375), live (following self-thinning,n = 459), and live + standing dead (survivors plus most recent mortality,n = 716). The Dirichlet-Thiessen tessellations of these maps indicated that the distribution of tile areas (area potentially available) becomes increasingly equitable over time. A significant positive correlation between diameter at breast height of surviving trees and their area potentially available was found for each map; this correlation was highest for the live tessellation. In the live + dead and live + standing dead tessellations, the mean tile area of dead trees was significandy smaller than that of survivors. The spatial pattern of diameter at breast height values of survivors revealed a positive autocorrelation: larger trees tend to have large neighbours and smaller trees have small ones. These results suggest a model of differential mortality in which the smaller individuals in a stand, particularly those surrounded by larger individuals, are most likely to die over a given time interval.

ISSN:0008-4026    

DOI:10.1139/b89-339

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

One small monocotyledon petiole, 1.8 × 1.5 mm wide, has been recovered from the Princeton chert in the Middle Eocene Allenby Formation, British Columbia. The petiole, rectangular in transverse outline, shows approximately 36 circular to oval-shaped vascular bundles within aerenchymatous ground tissue that includes tannin cells. The epidermis is underlain by a discontinuous hypodermis of thick-walled, pitted cells. Vascular bundles are in five series: (I) a median U-shaped arc of 11 – 13 bundles; (II) an abaxial arc of 6 bundles located below the main arc; (III) two short abaxial arcs of 3 bundles each; (IV) 2 bundles just below the abaxial surface; and (V) an adaxial series of 7 bundles that show an inverse orientation to those bundles in series I–IV. Larger bundles are collateral, with a protoxylem lacuna encircled by a ring of 9 – 14 thin-walled parenchyma cells, a relatively well-developed phloem strand, and one to three thin-walled metaxylem elements. Based on bundle arrangement, orientation, and morphology, the fossil petiole most closely resembles those of the Butomaceae and Alismataceae. This new species,Heleophyton helobiaeoidesErwin and Stockey gen. et sp.nov., in the Princeton chert flora, documents the presence of the Alismataceae in the Middle Eocene of western North America and provides further evidence that the locality represents an ancient aquatic ecosystem.

ISSN:0008-4026    

DOI:10.1139/b89-340

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Cutting down close the stalks ofBuddleiain February has resulted in an immediate development of populations of offshoots. Most of them would flower before the year was out. All of them, even those that remained vegetative, branched out and the branching showed mesotonous dominance. This was expressed, in the median zone, as a more pronounced increase in length of only one of the two branches at each node (stronger branch) rather than as an increase in leaf production. Reproductive branches are strong energy consumers; actually, they combinerstrategy (seed production) withKstrategy (pronounced cauline growth for space occupancy). Vegetative branches, weak energy consumers on which, however, leaves are particularly abundant, might serve as suppliers of metabolites. A nutritional equilibrium is perhaps achieved in a similar manner at the level of the stumps by the division of physiological roles between vegetative and reproductive offshoots. [Journal translation]

ISSN:0008-4026    

DOI:10.1139/b89-341

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

A mild, 2-h cold shock treatment, from 24 to 16 °C, was applied during the different stages ofMarsilea vestitaembryogenesis. For each main stage (proembryo, globular embryo, and completed embryo with a bilateral symmetry), cold-induced modifications in RNA and protein synthesis were studied by autoradiography of the cells after incorporation of [5-3H]uridine and [3H]leucine. In both controls and treated specimens, proembryogenesis was characterized by a lack of transcriptional activity and no labelling was detected in the cytoplasm until the 16-cell stage. Even in the absence ofde novoRNA synthesis in cooled samples, proteins necessary for the first cleavages of the embryo were being synthesized, but always at a rate lower than in the reference material. These results lead us to postulate that long-lived mRNA is stored in the cytoplasm of young embryos. Transcription, slowed down by the cold treatment, starts at the 8- to 16-cell stage and increases during the globular embryo stage. In lowered temperature conditions, transport of new RNA transcripts to the cytoplasm, which was strongly inhibited during the transition from the 16- to the 64-cell stage, appears to be less sensitive to cold shock as the embryo gets older. Our results show a difference in the response to temperature between RNA and protein synthesis. However, in both cases, sensitivity to cold temperature stress decreases with age. It is the physiological status reached by the embryo when the cold temperature stress is applied that determines the intensity of the response. [Journal translation]

ISSN:0008-4026    

DOI:10.1139/b89-342

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

EndogenousE-coniferin was characterized chemically and found to accumulate in cambia ofPicea glauca,Pinus banksiana,Pinus strobus, andLarix laricinaat the time of resumption of springtime cell-division activity and well before the initiation of lignification in differentiating tracheids. Coniferin content, quantified by high performance liquid chromatography, was highest on the centripetal side of the cambium, in developing xylem, at time of radial expansion of cambial derivatives. Stem ringing resulted in coniferin accumulation above the ring and disappearance below the ring. Coniferin was absent from leaves and dormant cambia. Exogenous coniferin was metabolized rapidly byin vitrocultures ofP.strobuscambium grown on a defined medium containing the auxins 1-naphthalene acetic acid and indol-3-yl acetic acid and the cytokinin benzylaminopurine. The evidence suggests coniferin content of the cambium will be of practical value for determining commitment to and competence for wood formation in conifers.

ISSN:0008-4026    

DOI:10.1139/b89-343

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The acid-secreting trichomes of chickpea (Cicer arietinumL.) were composed of 18 cells, including 1 basal cell, 3 elongate stalk cells, and 14 head cells. A subcuticular secretion chamber with cuticular pores was present above the head cells at the trichome tip. The basal and stalk cells had large central vacuoles, endoplasmic reticulum, mitochondria, and small vacuoles. In the stalk cells, these small vacuoles were aligned along microtubles extending from the bottom to the top of the cells. Head cells had more dense cytoplasm than stalk cells and also had numerous mitochondria and small vacuoles. A labyrinth of tubules and vesicles at the edges of the head cells contained granular material similar to that observed in the extraplasmic space of the head cell and in the secretion chamber. In older head cells, the tubules were thinner and lacked granular material, the cells contained sequestering membranes and vacuoles, and calcium oxalate crystals were observed in the extraplasmic space. Plasmodesmata were not observed between the basal cell and the surrounding mesophyll cells, although numerous plasmodesmata with associated desmotubules and endoplasmic reticulum connected the trichome cells. Chloroplasts were not observed in the head or stalk cells, whereas the basal cell had small chloroplasts with reduced thylakoid networks and the mesophyll cells had large chloroplasts with well-developed thylakoids that may provide the fixed carbon for organic-acid secretion.

ISSN:0008-4026    

DOI:10.1139/b89-344

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Changes in little bluestem (Schizachyrium scoparium) plant cover and vesicular–arbuscular mycorrhizae (VAM) root colonization, VAM spore density, and mycorrhizal inoculum potential were examined across a gradient from open sand prairie to closed oak–hickory forest in central Illinois. Soil samples were collected randomly and from the rhizosphere of little bluestem. Significant negative rank correlations were found between tree basal area and percent aerial cover of little bluestem, VAM colonization of little bluestem roots, mycorrhizal inoculum potential, and VAM spore abundance. However, spore abundances for randomly collected and rhizosphere soil samples, VAM colonization, and mycorrhizal inoculum potential had significant positive rank correlations with little bluestem cover. Highest spore densities were associated with the open sand prairie dominated end of the gradient, with lower spore numbers being found within the closed forest. Rhizosphere and randomly collected soil samples had a decrease in VAM fungal species richness as the vegetation types approached that of a closed forest community; however, dominant VAM fungal species were present throughout the gradient. Observed relationships between colonization, mycorrhizal inoculum potential, spore abundances, and little bluestem cover suggest interdependencies between host plant and associated mycobionts and (or) similar responses to environmental factors.

ISSN:0008-4026    

DOI:10.1139/b89-345

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Randomly collected mangrove wood and wood blocks ofAvicennia albaandAvicennia lanatasubmerged for 60 weeks in Mandai mangrove, Singapore, were investigated for marine fungi. Very frequent species on the random samples wereHalosarpheia retorquensandLignincola laevisand on the submerged wood blocks wereDidymosphaeria enalia,Lignincola laevis,Lulworthiasp. 1,Aigialus parvus,Aniptodera marina,Halocyphina villosa, and Ascomycete No. 25. The fungi growing on the wood blocks showed a pattern of succession, withL.laevisas an early colonizer,D.enaliaandLulworthiasp. 1 intermediate colonizers, andA.parvusa late colonizer. The variations in the results obtained from the two sampling methods are also discussed.

ISSN:0008-4026    

DOI:10.1139/b89-346

出版商:NRC Research Press    

年代:1989

数据来源: NRC