摘要:

Mathematical growth analyses were carried out on two C4grasses,Echinochloa crus-galliandEleusine indica, to test the influence of CO2enrichment and temperature on growth.Echinochloapopulations from Québec, North Carolina, and Mississippi and a single population ofEleusinefrom Mississippi were grown for 48 days at two CO2concentrations (350 and 675 μL∙L−1) and three temperature regimes (28:22, 24:18, and 21:15 °C). CO2enrichment generated an increased root dry weight and induced an earlier development of inflorescences. Net assimilation rate, the only other parameter to respond to CO2enrichment, was higher for plants grown at high CO2concentrations during the first harvest interval. Biomass partitioning was affected by temperature. Root dry weight was greater in plants grown at 21:15 °C while more leaf area was produced in warmer temperature regimes. Only plants from Québec maintained normal growth rates under the 21:15 °C regime, suggesting that northern C4plants are better suited for growth at low temperatures than southern one

ISSN:0008-4026    

DOI:10.1139/b85-206

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The vascular plant vegetation on activeSphagnumhummocks, on senescent hummocks, and in hollows of an Alaskan peatland was measured in several ways. Aboveground biomass and net primary production were greatest on senescent hummocks. Growth of hummock-formingSphagnummosses caused a significant increase in stem density and adventitious shoot production ofLedum palustreandAndromeda polifolia, whileVaccinium vitis-idaeashowed a decrease in stem density;Rubus chamaemoruswas unaffected. Overgrowth of vascular plants bySphagnumresulted in significantly higher leaf/stem ratios in most of the shrub species. In addition, leaf turnover rates of the evergreen shrubs were modified. The growth ofSphagnumhummocks leads to a developmental stage in the vascular vegetation in which a large amount of structural biomass is present relative to leaf biomass. The rate of microsuccessional change in hummock–hollow complexes appears to be relatively high, at least in comparison to those macrosuccessional processes associated with permafrost formation and melting.

ISSN:0008-4026    

DOI:10.1139/b85-207

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The avian dispersal system of red cedar, a low-quality, fleshy, cone-producing, woody plant, was investigated in southwest Virginia over a 2-year period. The red cedar cones ripened from late August through early October and persisted on the trees through May of the next year. Predispersal cone predation amounted to 0.9 and 3.1% of the total cone crop in 1980–1981 and 1981–1982, respectively. The proportion of the cone crop removed by avian dispersers was constant from year to year despite large differences in crop size. Active dispersal took place between November and March. Eight species of avian dispersers were identified. Single consistent feeders, such as the yellow-rumped warbler, accounted for slow, sustained removal of red cedar cones, whereas flock feeders, such as the cedar waxwing, European starling, and American robin, were responsible for rapid removal of entire cone crops. Bird-passed seeds showed 1.5–3.5 times greater total germination than manually depulped seeds. Average dispersal efficiency, defined as the proportion of the cone crop dispersed away (≥ 12 m) from the parent tree, was 68%. The high dispersal efficiency of red cedar may be explained in part by the short duration of visits paid by avian dispersers to cone-producing trees, the high mobility of these dispersers, and the relatively long transit times for ingested seeds. High efficiency combined with enhanced germination of ingested seeds may promote the rapid invasion of abandoned pastures by red cedar in the southeastern United States.

ISSN:0008-4026    

DOI:10.1139/b85-208

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The apical and floral development ofClaytonia carolinianavar.carolinianahas been studied concurrently with soil temperature, in a sugar maple forest of the Stoneham mountain, Québec. Apical cellular activity begins early in May, while the flowering stems of the year are present. At the beginning of July, external apical development becomes visible. In the first days of August, 9 months before flowering, the foliar and floral structures of the next year are already present in the soil. Meiosis takes place at the beginning of October and first pollen mitosis follows shortly after, in the middle of the same month. From that time, well developed individuals, without chlorophyll, are present just under the litter. They can occasionally turn green and reach the upper surface of the litter in November or December, where they will spend wintertime under the snow, at a temperature oscillating between 0 and −4 °C. This behaviour is quite close to the survival strategy of hemicryptophytes. The active epigeous growth period begins in the middle of April, with the melting of snow. Second pollen mitosis and flowering take place at this time, rapidly followed by seed setting, dissemination, and destruction of the aerial portion of the plant. Cytoecological investigations to study possible influence of environmental factors on chromosomal anomalies in primordia should thus be conducted during the year preceding the flowering ofClaytonia.

ISSN:0008-4026    

DOI:10.1139/b85-209

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Infectivity, measured as propagule numbers and root colonization rates, and effects on plant growth of indigenous vesicular–arbuscular fungal populations varied among soils from 10 different localities in Burgundy. These three characteristics of the populations were not necessarily related to each other nor to the physicochemical properties of the soils. It was possible, using relatively simple methods, to assess the potential for vesicular–arbuscular fungal inoculation in the different soils.

ISSN:0008-4026    

DOI:10.1139/b85-210

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The life cycle of a chytridiomycete,Sorochytrium milnesiophthoragen. et sp. nov., infecting the tardigradeMilnesium tardigradum, is described. The zoospores are posteriorly uniflagellate and ovoid, and possess a central mass similar to a nuclear cap. To initiate an endobiotic infection they attach to the cuticle of the host, encyst, and generate an appressorium. The appressorium forms a penetration tube which crosses the cuticle to the epidermis and enlarges at the tip into a spherical thallus. Concomitantly, vacuoles replace the cytoplasm of the cyst and appressorium. As the thallus enlarges, it moves into the body cavity and cleaves into segments. The segments separate and round up into incipient sporangia. The incipient sporangia develop branching rhizoids in conjunction with host death. After a period of growth the sporangia form inoperculate exit papillae which penetrate the host cuticle. Zoospores exit individually and fully formed. The fungus can develop a polycentric phase when freshly collected, dead hosts containing sporangia are cultured in habitat water or on nutrient agar. The growth is extramatrical, covering the surface of the old host. It is rhizoidal, branching, and nonseptate with numerous intercalate incipient sporangia bearing rhizoids. On nutrient media the thallus grows indefinitely while in habitat water the incipient sporangia mature and discharge motile spores. The spores frequently have two to five flagella and are larger than those of the endobiotic colonial phase. A similar polycentric growth develops when motile spores are isolated on nutrient medium and suggests that the extramatrical growth on the host originates from encysted spores.

ISSN:0008-4026    

DOI:10.1139/b85-211

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Cytological and physiological comparisons between autofluorescence and haloes which appeared at penetration sites of appressoria ofErysiphe graminisandErysiphe pision barley coleoptiles were made using dye stains and fluorescence microscopy. Haloes induced by these fungi on barley coleoptiles were successfully detected by various dyes when the inoculated coleoptiles were treated with 70% ethanol at 80 °C for 30 min before staining. Responses of haloes on coleoptiles to basic and acid dyes were very similar to those on barley leaves which have been reported earlier. In time-course studies, haloes were not detected until at least 15 min after initiation of cytoplasmic aggregation. The occurrence of haloes was suppressed by supplemental Ca2+, but unaffected by K+, Na+, and Li+. Similar results were obtained in haloes induced by both fungi. Autofluorescent regions remainedin situafter the inoculated coleoptile cells were plasmolyzed, suggesting that this phenomenon might be closely associated with host cell walls. As reported earlier, autofluorescence preceded the appearance of cytoplasmic aggregates by 1–10 min and, moreover, its appearance was enhanced by divalent cations such as Ca2+, Mg2+, and Mn2+, but not by monovalent cations such as K+, Na+, and Li+. Based on these results and earlier studies, it was concluded that the autofluorescence and haloes represented different responses in host cell walls to the penetration activities of both pathogenic and nonpathogenic fungi.

ISSN:0008-4026    

DOI:10.1139/b85-212

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Light and electron microscopic observation of laticifers in fruits of periwinkle,Catharanthus roseus(L.) G. Don, revealed cells which after fixation showed an abundance of droplets in vacuoles. The droplets have a rough surface and are electron dense. A comparison of cytoplasm of laticifers and neighboring parenchyma cells indicated varying degrees of degradation of organelles. Degradation visibly affects the nuclei, plastids, and mitochondria. Latex contains electron-dense droplets and some vesiculated cytoplasm with highly degraded organelles interspersed. Vindolinine and 19-epivindolinine, but not vindoline, were found to be the main alkaloids of periwinkle fruit latex.

ISSN:0008-4026    

DOI:10.1139/b85-213

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Potted peach trees (Prunus persica(L.) Batsch cv. Loring) were mechanically defoliated and the influence of temperature on formation of the primary protective layer and phellogen generation in the leaf abscission region was examined histologically. Plants maintained at 7.5, 12.5, and 17.5 °C showed first indications of primary protective layer formation at 18, 9, and 6 days, respectively. Subsequent generation of phellogen and the appearance of the first phellem cell were observed at 30, 18, and 12 days, respectively. The primary protective layer formed approximately 700 μm proximal to the separation zone and was composed of cells with lignified walls and thin suberin linings.

ISSN:0008-4026    

DOI:10.1139/b85-214

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Cultural characteristics observed in nearly 75 cultures were the basis for the descriptions of the four North American species ofHericium. Comparison of the cultural characters showed subtle differences among the species. Similarities in cultural characters led to the evaluation of nearly 4100 intercollection matings to confirm the identity of the cultures and establish species circumscriptions. As a result all Canadian cultures labelledH.erinaceuswere reassigned toH.americanum. The presence ofH.erinaceusin Canada could not be confirmed. Matings confirmed the conspecificity of North American and European cultures ofH.coralloidesandH.erinaceus. Intracollection matings established or confirmed thatH.abietis,H.americanum,H.coralloides, andH.erinaceushave a bifactorial mating system.

ISSN:0008-4026    

DOI:10.1139/b85-215

出版商:NRC Research Press    

年代:1985

数据来源: NRC