植物雄性不育类型的分析

本文论述了植物雄性不育的类型、原因、诱导和应用,总结了国内外在这方面的研究成果。重点对植物雄性不育的类型给以分析,从而丰富了遗传多样性的内容,展示了雄性不育理论和应用研究的光明前景。     

Fire and competition in Australian heath: a conceptual model and field investigations

Abstract. We describe a model of heath vegetation, in which species were classified into five functional groups based on characteristics of their propagule pools, post-fire growth, timing and mode of reproduction and competitive status. The model assumes no recruitment without fire and a simple competitive hierarchy based on vertical stature. A critical feature of the model is an initial post-fire window of 5–6 yr in which competition from overstorey species on understorey species is reduced. Understorey functional groups differ in their ability to exploit this window. In the field, we tested five predictions derived from the model: (a) overall species richness of understorey varies inversely with overstorey density as a result of a trend in richness of woody species, but not in herbaceous species; (b) where an overstorey was present in the previous fire interval, post-fire population density is reduced in a functional group of understorey serotinous resprouting shrubs, but not in a group of understorey obligate-seeding shrubs with soil seed banks; (c) in understorey serotinous resprouting shrubs, post-fire regrowth in resprouting individuals is adversely affected by the presence of an overstorey in the preceding fire interval; (d) in understorey serotinous resprouting shrubs, levels of pre-fire propagules are lower in the presence of an overstorey, reducing the density of post-fire recruits; and (e) in understorey serotinous resprouting shrubs, recruitment relative to the pre-fire population is unaffected by overstorey species within the window of reduced competition. Of these, three tests (a,b,d) supported the model, one (e) may support the model, but the results were inconclusive and one (c) did not support the model. Limitations and further applications of the model are discussed. Our results suggest that maintenance of high densities of overstorey populations is in conflict with conservation of some understorey species. Models of the type we propose will help identify and resolve such conflicts and promote the judicious use of fire to maintain full species diversity of plant communities.     

Effective population size,genetic diversity,and coalescence time in subdivided populations

A formula for the effective population size for the finite island model of subdivided populations is derived. The formula indicates that the effective size can be substantially greater than the actual number of individuals in the entire population when the migration rate among subpopulations is small. It is shown that the mean nucleotide diversity, coalescence time, and heterozygosity for genes sampled from the entire population can be predicted fairly well from the theory for randomly mating populations if the effective population size for the finite island model is used.     

INFLUENCE OF NATURAL ULTRAVIOLET RADIATION ON LOTIC PERIPHYTIC DIATOM COMMUNITY GROWTH,BIOMASS ACCRUAL,AND SPECIES COMPOSITION: SHORT-TERM VERSUS LONG-TERM EFFECTS1, 2

Growth rates, accumulation dynamics, and species succession of periphytic diatom communities were examined in the presence and absence of natural ultraviolet (UV) radiation using a series of outdoor, continuous-flow experimental flumes located on the South Thompson River, British Columbia. In a short-term experiment (2–3 wk), log-phase growth rates of naturally seeded diatom communities comprised of Tabellaria fenestrata (Lyngb.) Kütz., T. flocculosa (Roth) Kütz., Fragilaria crotonesis Kitton, and F. vaucheriae (Ehr.) Peter. exposed to 90% ambient photosynthetically active radiation (PAR) + UV were 30–40% lower than growth rates under 90% PAR alone. UV inhibition of growth rate was independent of the degree of P limitation within the range of relative specific growth rates (μ:μ_max-P) of 0.5–1.0. In a long-term trial, inhibition of attached diatom accumulation under 90% PAR + UV during the first 2–3 wk was corroborated. Reduction of full sunlight to 50% PAR + UV prevented the initial inhibition phase. The initial inihibitory effect of 90% PAR + UV on algal accumulation was reversed after 3–4 wk, and by 5 wk total diatom abundance (chlorophyll a, cell numbers and cell biovolumes) in communities exposed to PAR + UV were 2–4-old greater than in communities protected from UV. Under 90% PAR + UV and 50% PAR + UV, a succession to stalked diatom genera (Cymbella and Gomphoneis) occurred. Species succession under UV radiation doubled the mean cell size of the diatom communities. The shift from inhibition to a long-term increase in the autotrophic community under PAR + UV compared to PAR alone provides further evidence against the use of short-term incubation experiments to define the long-term implications of increases in UVB. These results suggest that the ecological effects of present-day levels of UVB and UVB:UVA ratios on autotrophic communities are not well understood and might be mediated through complex trophic level interactions.     

Allozyme variation in stable flies (Diptera: Muscidae)

Polyacrylamide gel electrophoresis was used to resolve allozymes in the cosmopolitan blood-feeding stable fly,Stomoxys calcitrans (L.). Nineteen of 38 loci were polymorphic (53%). Mean heterozygosities among all loci and among only polymorphic loci were 0.096 and 0.182, respectively. These gene diversity measures are about half those among other muscid Diptera. Variation in gene frequencies was examined in 10 natural stable fly populations from Iowa and Minnesota. Gene frequencies were homogeneous at five of eight loci among six populations in 1990 and eight of eight loci among four populations in 1992. Wright'sF statistics showed no significant departure from random mating among stable flies. It was concluded that gene flow compensates for any local differentiation in stable fly populations.     

Stress and disturbance in the phytoplankton community of a shallow,hypertrophic lake

The validity of Connell's intermediate disturbance hypothesis in phytoplankton communities was tested on data from a hypertrophic, shallow lake, Hjarbæk Fjord, Denmark.The present data from Hjarbæk Fjord demonstrate the difficulties in distinguishing stress from disturbance in a phytoplankton community, and show that great changes in the phytoplankton community can take place within few days.A collapse of blue-green algae in late June 1986 caused remineralization of nutrients and resulted in a rapid increase of fast-growing small chlorococcal green algae and phytoplankton species diversity, without any external disturbances acting on the lake. External disturbances in the form of wind action and brackish water intrusion occurred several days after the onset of these events. Carbon depletion and pH 11.0 were severe stress factors on the phytoplankton community. They were induced by calm, warm weather, but eventually acted as a kind of disturbance to the normally well circulated lake.     

Seasonal fluctuations in the diversity and compositional stability of phytoplankton communities in small lakes in upper Bavaria

A study of diversity and compositional stability of phytoplankton communities during one vegetation period was carried out in small lakes in upper Bavaria. Shannon-Weaver diversity index was calculated on the base of number of individuals and on the base of biomass. On average, the diversity (annual mean) was highest in mesotrophic lakes. A comparison of three morphologically different (esp. exposure to wind, surface area and mean depth) lakes (Pelhamer See, Thalersee and Kautsee) sought to find out how the phytoplankton community structure reacts to events of intermediate disturbance, in terms of diversity- or biomass changes. Principal Component Analysis was used to measure the persistence of the phytoplankton association. The examples given in this paper led to these conclusions: High diversity or increase in diversity occur in compositionally instable communities, in high wind-stress events, with small algae and with high grazing. Low diversity or decrease in diversity occur in compositionally stable periods, when conditions select few species, as large forms dominate and as grazing by zooplankton takes effect. Gradual seasonal changes are observed in structurally stable lakes. In lakes exposed to frequent disturbances, seasonal changes may be dominated by intermediate responses.     

Seasonal succession of phytoplankton in a lake of the Paraná river floodplain,Argentina

Phytoplankton biomass, morphological and taxonomic composition, species diversity and productivity were analyzed in a shallow lake of the Middle Paraná River floodplain (El Tigre, 31 ° 41 S and 60° 42 W), between November 1986 and July 1988. Lake inundation (filling and through-flow phases) constituted an intense long-term perturbation in the physical and chemical environment. As the lake filled with river water, K-selected species (netplanktonic filamentous bluegreens, > 37 µm, with low surface area/volume (SA/V) ratios) that had existed prior to filling (late spring 1986) were replaced in summer-fall by r-selected species (nannoplanktonic chlorophytes and cryptophytes, < 37 µm, mainly stout forms with high SA/V ratios). During the through-flow phase, lentic phytoplankton was replaced by lotic flagellate populations due to the direct flushing by river water. During the period of falling water (drainage and isolation phases), nanoplanktonic algae with similar characteristics to those of the filling phase dominated in late winter-spring. Later in the isolation phase, these were succeeded by K-selected species (netplanktonic algae, mainly motile spherical dinoflagellates and filamentous bluegreens with low SA/V ratios). Simultaneously, primary production per unit biomass decreased and total biomass and specific diversity increased. Seasonal changes of phytoplankton in floodplain lakes can be interpreted as the interaction between true successional development (as observed in the drainage and isolation phases) and intermediate disturbance. Using Reynolds' terminology, short-term disturbance (slight inflow of nutrient-rich river water) caused reversion to an earlier stage in the former succession, and long-term disturbance (lake inundation) truncated the successional progression and a new (or shifted) succession was initiated.     

Effects of stripe rust on the evolution of genetically diverse wheat populations

Summary Eighteen populations, composed of four wheat (Triticum aestivum) varieties that were originally mixed together at equal frequencies, were grown for one-to-three generations at two locations. In addition, pure stands of the four varieties were grown in each year. Populations were either exposed to two stripe rust (Puccinia striiformis) races, protected from stripe rust, or exposed to alternating years of diseased and disease-free conditions. Regression of the logit of a variety's frequency versus generation number was used to calculate the relative fitness of each variety in each population. These analyses suggest that the relative fitnesses of the wheat varieties were affected by disease and geographic location and were constant over time. However, frequency-changes of varieties in the mixtures were negatively correlated with their planting frequencies (0.0001 < P < 0.085 in 14 out of 16 cases), suggesting that fitnesses were frequency-dependent in both the presence and absence of disease. We hypothesize that failure to detect frequency-dependence of fitness in the logit analyses was due to a limited number of generations and a limited range of initial variety frequencies. This is supported by data from longer-term studies in the literature that provide evidence for frequency-dependence of fitness in plant mixtures. Analyses of currently available field data suggest that stable equilibria may be a more likely outcome for mixtures of varieties that are more closely related and/or more uniformly adapted to the environment in which they are grown.Paper No. 9820 of the journal series of the Oregon Agricultural Experiment Station.