Size-Dependent Effects in the Analysis of Reproductive Effort in Plants

1986 ◽  
Vol 127 (5) ◽  
pp. 667-680 ◽  
Author(s):  
Douglas A. Samson ◽  
Kenneth S. Werk
Keyword(s):  
Reproductive Effort ◽  
Size Dependent

Comparison of size-dependent reproductive effort in two dandelion (Taraxacum officinale) populations

1998 ◽  
Vol 76 (1) ◽  
pp. 166-173 ◽  
Author(s):  
Clive VJ Welham ◽  
Robert A Setter
Keyword(s):  
Life History ◽  
Reproductive Effort ◽  
Seed Mass ◽  
Taraxacum Officinale ◽  
Reproductive Morphology ◽  
Size Dependent ◽  
Alfalfa Field ◽  
History Approach ◽  
Total Seed ◽  
Lower Ratio

Reproductive effort in dandelions (Taraxacum officinale Weber) from two different habitats was compared. One dandelion population occupied a 5-year-old alfalfa (Medicago spp.) field, an environment subject to regular disturbance but with a relatively low density of neighbours. Individuals from the second population were derived from a number of undisturbed sites where the density of neighbouring grasses was high. Three hypotheses were evaluated with respect to the observed patterns of reproductive effort. One hypothesis, that reproductive effort was a function of differences between habitats in resource availability, did not provide an explanation for our results. A second hypothesis considered patterns of reproductive effort when mortality rates varied with degree of disturbance and neighbour density, which was a consequence of each habitat representing a different successional environment. A third hypothesis used a life-history approach to predict reproductive effort when mortality schedules were size dependent. Both of these hypotheses received support for their predictions. There was more than a sixfold variation in reproductive effort among individuals from the alfalfa field and a fourfold variation on the undisturbed sites. Much of this variation, however, was attributable to a size-dependent relationship between reproductive effort and vegetative mass. Total reproductive effort (total seed plus scape mass) in both populations increased linearly with vegetative mass, but the slope for the population from the alfalfa field was significantly higher. In contrast, proportional reproductive effort (total seed plus scape mass per vegetative mass) showed a curvilinear increase for the alfalfa field population but was linear and negative for the undisturbed population. There were also important differences between the populations in reproductive morphology. Larger plants on the alfalfa field had longer average scape lengths, produced more flower heads (capitula) per plant, had greater seed production, and had a lower ratio of seed mass per pappus area; only mean scape and mean seed mass did not differ significantly. We suggest that dandelions on the alfalfa field have a different reproductive morphology to facilitate colonization of open areas on the field.Key words: Taraxacum, dandelion, reproductive effort, biomass, life history, neighbour density, agriculture, weed.

Size-dependent reproductive effort in Amaranthus retroflexus: the influence of planting density and sowing date

2006 ◽  
Vol 84 (3) ◽  
pp. 485-492 ◽  
Author(s):  
Tianhui Wang ◽  
Daowei Zhou ◽  
Ping Wang ◽  
Hongxiang Zhang
Keyword(s):  
Reproductive Effort ◽  
Branch Length ◽  
Sowing Date ◽  
Amaranthus Retroflexus ◽  
Planting Density ◽  
Size Dependent ◽  
Sowing Dates ◽  
Wide Range ◽  
Total Branch Length ◽  
Reproductive Biomass

Size-dependent reproductive effort is an important component of plant fitness. The responses of reproductive effort to environmental factors in Amaranthus retroflexus L. were measured in two experiments. A wide range of selection pressures were generated by manipulating the sowing date (29 April, 23 May, 18 June, and 14 July) and planting density (13.4, 36, 121, and 441 plants·m–2). Allometric analysis between reproductive biomass and vegetative biomass across treatments showed that reproductive effort increased with size in response to different planting densities but decreased with size in sowing dates experiment. The allometric exponent between treatments was not influenced by planting densities but had significant variation with sowing date. Total branch length could explain most of the variation of reproductive accumulation and allocation in planting density experiments. For the plants with different sowing dates, total branch length was the main determinant of reproductive biomass, while reproductive effort mainly depended on the number of primary branches per unit stem mass. Architectural constraints with size result in size-dependent reproduction. Size-dependent reproduction in A. retroflexus was influenced by available resources and environmental conditions through the mechanisms of self-regulation of architectural traits.

scholarly journals Effects of fertility, weed density and crop competition on biomass partitioning in Centaurea cyanus L.

2014 ◽  
Vol 68 (1) ◽  
pp. 69-77 ◽  
Author(s):  
Łukasz Chachulski ◽  
Sławomir Janakowski ◽  
Władysław Golinowski
Keyword(s):  
Reproductive Effort ◽  
Reproductive Investment ◽  
Plant Size ◽  
Biomass Partitioning ◽  
Winter Rye ◽  
Fertility Level ◽  
Size Dependent ◽  
Reproductive Structures ◽  
Centaurea Cyanus ◽  
Arable Weed

The influence of environmental factors on biomass partitioning of annual arable weed <em>Centaurea cyanus</em> was analysed. We investigated the effect of fertilisation, density and competition with the winter rye crop on the reproductive investment. Three fertiliser treatments and three density levels were applied. In <em>Centaurea cyanus</em> differences in the pattern of biomass allocation to reproduction are related to plant size. The relationship between reproductive and vegetative mass is close to linear. It is consistent with the model of linear size-dependent reproductive output. In <em>Centaurea cyanus</em> this model worked well for size differences that have been generated by interspecific competition, nutrients supply and density. Our data support the hypothesis that plastic changes in relationship between vegetative and generative biomass are environmentally-induced. Significantly different relationship between vegetative and reproductive biomass were detected among populations growing at different density and fertility levels. The fertilisation with mineral fertiliser and manure resulted in an increase of generative biomass allocated to flowerheads and a decrease of reproductive effort. Generative dry weight increased more rapidly with plant size in higher densities of population and at lower fertility levels. The experiment showed that the rate of weight allocated to reproductive structures was bigger under the pressure of competition with cereal crop. At low fertility level and high density, when the individuals were small, generative biomass increased faster with plant size. The production of seeds was not directly dependent on biomass allocated into total reproductive structures. At low level, of nutrient supply <em>C. cyanus</em> gave more offspring per gram of its biomass. We discuss the results in context of life-history theory. From the strategic point of view, size-dependent variation in reproductive effort and in efficiency of reproduction can be interpreted as good tactics to favour high reproductive investment in small individuals, thus ensuring some offspring. Such a strategy is due to developmental constraints like short vegetation, the small amount of resources available and strong competition with crop.

Production and STEM examination of controlled-size silver clusters

1983 ◽  
Vol 41 ◽  
pp. 338-339
Author(s):  
M. A. Listvan ◽  
R. P. Andres
Keyword(s):  
Cluster Size ◽  
Metal Clusters ◽  
Experimental Parameter ◽  
Carbon Films ◽  
Metal Species ◽  
Silver Clusters ◽  
Free Jet ◽  
Size Dependent ◽  
Cluster Properties ◽  
Controllable Size

Knowledge of the function and structure of small metal clusters is one goal of research in catalysis. One important experimental parameter is cluster size. Ideally, one would like to produce metal clusters of regulated size in order to characterize size-dependent cluster properties.A source has been developed which is capable of producing microscopic metal clusters of controllable size (in the range 5-500 atoms) This source, the Multiple Expansion Cluster Source, with a Free Jet Deceleration Filter (MECS/FJDF) operates as follows. The bulk metal is heated in an oven to give controlled concentrations of monomer and dimer which were expanded sonically. These metal species were quenched and condensed in He and filtered to produce areosol particles of a controlled size as verified by mass spectrometer measurements. The clusters were caught on pre-mounted, clean carbon films. The grids were then transferred in air for microscopic examination. MECS/FJDF was used to produce two different sizes of silver clusters for this study: nominally Ag6 and Ag50.

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