摘要:

During the past few decades, attempts to manage excessive abundance of freshwater macrophytes, decreasing abundance of marine eelgrass (Zostera marinaL.), and abundance and diversity of seaweeds have yielded modest successes, some short-term recoveries, and other complete failures. As many broad principles apply to the management of all aquatic plants, the aim of this paper was to synthesize the issues and provide direction for the management of freshwater rooted macrophytes, eelgrass, and marine macrophytic algae and place them in a Canadian context. Specifically, we examine biomass and landscape objectives for macrophyte management, assess the role of environmental manipulation for the management of macrophyte assemblages, and provide direction for managing macrophyte assemblages within the context of ecosystem sustainability. Finally, we advocate that, given the unexpected outcomes that may arise from uncontrolled events (e.g., weather, inherent variability in life history characteristics), management interventions should be designed in such a way that it is possible to make valid conclusions about the outcome of any given management action (i.e., design the management action to be a scientific experiment).Key words: macrophyte, algae, eelgrass, herbivores, nutrients, landscape ecology.

ISSN:0008-4026    

DOI:10.1139/b99-092

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Ninety-seven percent of theRhexia marianaL. seeds collected in Tennessee were physiologically dormant at maturity in autumn, and they became nondormant during stratification. Light was required for germination, and seeds germinated to higher percentages on filter paper than on sand. Seeds buried in soil in October 1992 and 1994 and exposed to natural seasonal temperatures were exhumed and tested for germination at monthly or bimonthly intervals for 30 and 32 months, respectively. Seeds gained the ability to germinate to 80% or more at 30:15 and 35:20°C during the first winter of burial and also at 25:15°C during the second winter, but they did not re-enter dormancy. In contrast, seeds incubated at 20:10°C exhibited an annual cycle of moderate to high germination percentages in winter-spring and low germination percentages in summer-autumn. Thus, germination can occur at habitat temperatures in Tennessee from April to September. This is the first report of physiological dormancy in seeds of the Melastomataceae in the temperate region. Like members of many plant families in temperate eastern North America, seeds ofR. mariana(i) show a decrease in the minimum temperature for germination as they come out of dormancy and (ii) exhibit some seasonal variation in the temperature range for germination. Thus, these dormancy or germination characteristics appear to be adaptations of species to the climatic conditions in temperate eastern North America.Key words: seed dormancy, seed germination, dormancy cycles, buried seeds, Melastomataceae,Rhex

ISSN:0008-4026    

DOI:10.1139/b98-223

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

A recessive mutation in theRHD4gene ofArabidopsis thalianaL. affects the control of tip growth in seedling root hairs. Fully grownrhd4root hairs are half the length of wild-type (WT) hairs. The hairs are wider, and they vary in diameter during tip growth. Light microscopy and motion analysis revealed thatrhd4hairs grow more slowly and that hair growth rate varies more than in WT hairs. Hair diameter increases at therhd4hair tips when tip growth slows. Ultrastructural analysis revealed cell wall thickenings in some mutant hairs. WT hairs were grown in a hyperosmotic medium in an attempt to mimic therhd4hairs and investigate the control of root hair morphology. Osmotic stress increased WT hair diameter and induced hair bulging and also increased the diameters ofrhd4hairs. Osmotic stress could disrupt tip growth through reduced turgor pressure and (or) reduced concentrations of cytosolic calcium. Together these results indicate thatRHD4is required to maintain a uniform rate of tip growth in root hairs.Key words:Arabidopsis thaliana, cell wall, cryofixation, mutant, root hairs, tip growth.

ISSN:0008-4026    

DOI:10.1139/b99-010

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

In the annual species,Crepis sancta(L.) Bornm., peripheral and central florets of the capitulum yield achenes that differ in mass, colour, morphology, and in the presence-absence of pappus. To examine the consequences of seed dimorphism on dispersal in time in this species, I compared the viability of central and peripheral achenes stored for up to 5 years. Both the germination percentage and the early seedling survival of both morphs decreased progressively with duration of storage. However, the loss in viability was lower for peripheral achenes than for central ones. Furthermore, two independent experiments showed that peripheral achenes have reduced dispersal ability, whereas the pappus unit of central achenes confers greater dispersal ability. These differences between achene types may explain the persistence of this colonizing species in communities dominated by perennial species, which is a major ecological feature ofC. sancta.Key words: dispersal, dormancy, mixed strategy, secondary succession.

ISSN:0008-4026    

DOI:10.1139/b99-011

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Seedlings ofSalix eriocephalaMichx.,Salix sericeaMarsh., and their F1hybrids were tested for their growth under contrasting water conditions. One-year old seedlings were grown in pots and subjected to one of two experiments, a scheduled-watering experiment (watered every 1, 4, 8, or 12 days) or a dry-down experiment (no watering after an initial period without water limitation). In the scheduled-watering experiment, short-term growth of hybrids was suppressed relative to the parents. However, subsequent watering allowed hybrids to recover. By the end of the 48-day experiments, hybrids exhibited heterosis across all treatments. In the dry-down experiment, hybrids again were highly susceptible to the onset of drought conditions. From these results, we hypothesize that temporal and spatial variability in water availability could determine the survivorship of hybrids and the frequency of introgression; high water availability may enhance the relative performance of hybrids, while low water availability may limit hybrids.Key words: Salicaceae, willows, hybridization, water relations, performance, heterosis.

ISSN:0008-4026    

DOI:10.1139/b99-021

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

We determined in a greenhouse experiment whether experimental defoliation of the host affects the performance of the parasitic plant and whether the effects on the success of the parasite depend on the host species. We also asked whether two species of grass hosts differ in response to simultaneous defoliation and hemiparasitic infection. The experiment had a complete 2 × 3 × 2 factorial design, with host species (Poa annuaL. orPoa pratensisL.) combined with defoliation (undefoliated, 50% defoliated, or 100% defoliated) and hemiparasitic infection (parasitized or unparasitized). Defoliation reduced the final biomass of both host species. However, total biomass and the number of flowers produced by the hemiparasiticRhinanthus serotinus(Schönh.) Oborny was reduced only when the host wasP. annuaand when the host was completely defoliated.Rhinanthusinfection significantly decreased the final biomass of both host species. However, the two hosts differed in their responses: the biomass of undefoliatedP. annuaplants was reduced four times more than that of undefoliatedP. pratensisplants. The results indicate that the relative value of different host species depends on the intensity of defoliation.Key words: root hemiparasite, host defoliation, host-parasite interaction,Poa annua,Poa pratensis,Rhinanthus serotin

ISSN:0008-4026    

DOI:10.1139/b99-012

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

InLarix kaempferi(Lamb.) Carr. andL. ×eurolepisA. Henry, a secretion fills the micropylar canal of the ovule during a period of archegonial development that ranges from central cell stage until fertilization. Dissection of the ovuliferous scales caused excess fluid to be exuded from the micropylar canal, forming a drop at the tip of the micropyle. This drop was collected, and its production was quantified. Drop volume was recorded, and the percentage of ovules with drops was counted. The maximum volume of 217 nL far exceeded the volume of the micropyle, which ranged between 18 ± 8 and 28 ± 7 nL (mean ± SD). Removal of drops resulted in further drops being secreted. No drops were produced in ovules that had aborted megagametophyte development.Key words:Larix, micropylar secretions, ovule development

ISSN:0008-4026    

DOI:10.1139/b99-014

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

We examined phloem injury and repair over an 8-day period following probing (feeding with piercing-sucking mouthparts inserted in plant) by the potato leafhopper,Empoasca fabae(Harris) (Homoptera: Cicadellidae), in stems of alfalfa,Medicago sativaL. A videomicrography technique was used to apply standard-duration probing by potato leafhoppers on alfalfa stems. Leafhopper-induced plant responses, observed using transmission electron microscopy and fluorescence microscopy, included phloem cell wall loosening and collapse, increased cytoplasmic density and dissolution of necrotic phloem cells, enlargement of nuclei and nucleoli in surviving cells, increased mitotic activity, thickening of phloem cell walls, formation of short and irregularly shaped wound sieve elements (often with side-wall sieve plates), accelerated chloroplast maturation and formation of abnormally large starch grains, and generation of phloem transfer cells from companion cells. Aniline blue staining of callose in sieve elements revealed that wound sieve tubes circumvented damaged phloem by 8 days after leafhopper-induced injury. These new sieve tubes often developed in the interfascicular area adjacent to the wounded bundles.Key words: plant wound response, wound phloem, sieve element, transfer cell, leafhopper feeding,Empoasca fabae,Medicago sativa.

ISSN:0008-4026    

DOI:10.1139/b99-005

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Stem tissue of resistant and susceptible genotypes ofPopulus tremuloidesMichx. wounded or wound-inoculated withEntoleuca mammata(Wahlenberg: Fr.) J.D. Rogers & Y.-M. Ju was prepared for histochemical and microspectrophotometric analysis. Samples were collected over a 96-h period. Parenchyma cell walls associated with the response zone of infected resistant and susceptible genotypes accumulated phenolic substances having lignin-like properties. Features of the lignified zone distinguished resistant from susceptible genotypes. This zone in the resistant genotype was uniformly lignified, while in the susceptible genotype, it was discontinuous. Wound callus developed in the infected resistant but not in the susceptible genotype. In the former, callus developed internal to the lignified zone, contained phenolic substances, and was visible 48 h after inoculation. In the susceptible, callus failed to develop. Wounded tissue of both genotypes displayed no distinguishing response characteristics. Both produced equivalent amounts of callus, accumulated similar levels of lignin-like substances, and deposited it in identical locations. It is concluded that resistantP. tremuloideslimits infection byE. mammataby two distinct mechanisms: (i) by the development of an intact and localized lignified barrier zone and (ii) by the development of wound callus rich in phenolic substances. The susceptible is ineffective at developing either of these barriers.Key words: aspen, Hypoxylon canker, disease resistance.

ISSN:0008-4026    

DOI:10.1139/b99-017

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

This study examines the ratio of wind to insect pollination of five alpine-arcticSalixspecies and possible correlations between plant traits and this ratio. The field work was done in an alpine area in southwest Norway, at an elevation of 1250 m. Female catkins were enclosed within mesh cloth to prevent insect visitation, and their fruit set was determined and compared with that of open-pollinated control catkins. Simultaneously, pollen production per anther, pollen dispersal, standing crop of nectar, flower length, number of flowers per catkin, and catkin length were measured. The amount of wind pollination of the species varied from 2 to 52%. All species spread pollen in the air. Nectar content, catkin length, flower number, and flower length showed a negative relationship with the percentage of wind pollination. Significant negative linear correlations between female catkin length and flower length and amount of wind pollination were detected. Pollen production per anther did not show any relationship to the pollination system. We suggest that the evolution to insect pollination in alpineSalixspecies may have resulted in a lengthening of anthers and pistils, and an increase in nectar production.Key words: alpine, anemophily, entomophily, floral traits, pollination,Salix.

ISSN:0008-4026    

DOI:10.1139/b99-003

出版商:NRC Research Press    

年代:1999

数据来源: NRC