Achene Production Research Articles

Environmental Correlations with Male, Female and Clonal Biomass Allocation in the Forest Herb, Laportea canadensis

-Hypotheses predicting biomass allocation to male reproduction, female reproduction and clonal growth in different environments are tested for Laportea canadensis, a wind-pollinated, rhizomatous, monoecious herb of floodplain and mesic upland forests. Different environments in floodplain forests are associated with Laportea's allocation to male (fast drainage) vs. female (favorable growing conditions late in the season: heavy soil, high light and low density). In upland forests, both male and female allocations increase with productive conditions (high light and intermediate soil texture). Vegetative allocation decreases with stem density in upland forests, corresponding to the strawberry-coral model of Williams. All types of reproduction are size-dependent in Laportea. However, male reproduction requires larger minimum sizes than female reproduction, probably reflecting selection for longer distance wind-pollination. Clonal growth in Laportea allows persistence in dark upland areas with high amounts of litter, where seedling establishment is difficult. Upland plants also devote relatively little biomass to sexual reproduction and achene production. Reproductive specialization between male and female function within floodplains, and between fruit production and clonal spread within floodplains and between habitats, contributes to the competitive success of this species.

Ecological studies on Potamogeton pectinatus L. III. Reproductive strategies and germination ecology

This third paper on the ecology of Potamogeton pectinatus L. deals with the reproductive strategies of different populations of this species. The various ways of propagation and survival, both generative and vegetative, are described. Attention is also given to the germination ecology of achenes and tubers. Flowering and achene production have been observed in most populations studied and the process of fructification is described in detail. Inflorescences of P. pectinatus are surface pollinated and the pollen is hydrophobous. The formation of seed banks by populations appears to be largely dependent on the degree of shelter in the habitats, the number of achenes produced seems to be less important. The results of the germination experiments with achenes support the field observations, indicating that achenes are relatively unimportant in the shory-term survival of populations. The main function of these generative propagules is most likely the dispersal of the species and the long-term survival. Potamogeton pectinatus shows several types of vegetative propagation. Subterranean tubers are the most common and most important propagules. Temperature and stratification appear to be major factors regulating the germination of tubers. The reproduction of P. pectinatus is discussed in relation to the life cycle and survival strategy of the populations.

Ecological studies on Potamogeton pectinatus L. I. General characteristics, biomass production and life cycles under field conditions

In this first part of a series on the ecology of Potamogeton pectinatus L., some general characteristics of the species and its habitats are recorded. The morphological characteristics of this phenoplastic species vary considerably under different environmental conditions. The taxonomy of the species remains unclear and complicated. The biomass allocation between different plant parts in the course of the year varies considerably between populations. In a sheltered brackish habitat in The Netherlands P. pectinatus showed a perennial life cycle and produced a maximum standing crop of 1312.5 g dry weight (DW) m −2 (1062.3 g ash-free dry weight (AFDW) m −2). In a relatively large and wind-exposed freshwater habitat the period of growth was very short and the maximum standing crop reached only 73.2 g DW m −2 (49.0 g AFDW m −2). In the Laiwersmeer (The Netherlands) foraging by waterfowl reduced the maximum shoot standing crop of a P. pectinatus bed to 17% of that of an ungrazed bed. In the Camargue (France) regulation of the water level had a distinct effect on the biomass development of a P. pectinatus population. In the Camargue all populations studied showed a perennial life cycle, although in larger brackish waters the biomass decreased considerably during autumn and winter, probably because of waterfowl grazing. The maximum standing crop varied from 375.7 to 668.0 g DW m −2 (275.2–549.8 g m −2 AFDW) in different habitats in the Camargue. Data on populations in Finland and on populations of running waters in The Netherlands are also presented. All populations studied showed flowering and achene production under field conditions, except for those in running waters. Although sometimes a considerable achene production occurred (20.4 g DW m −2, 18.4 g AFDW, 3707 achenes m −2 in the Baisse Salée, Camargue) all populations reproduced mainly vegetatively. The main function of the achenes appears to be dispersal and long-term survival of the species. The tubers played a very important role in the survival of populations. Populations of brackish waters predominantly produced single tubers and only rarely double tubers (less than 2%). Freshwater populations produced 30–60% double tubers under field conditions. Although reproduction is generally vegetative, it is argued that distinct annual and perennial life cycles can be recognized. Different life cycles can be induced by various environmental conditions. Life-cycle characteristics of several aquatic macrophytes are reviewed and it is concluded that basic information on life cycles and reproductive strategies of many aquatic macrophyte species is still lacking.

The Ecology of Seed Heteromorphism in Heterosperma Pinnatum in Central Mexico

Heterosperman pinnatum is an annual composite that produces heteromorphic achenes, with the proportion of achene morphs varying geographically. Field, greenhouse, and laboratory experiments were used to examine the ecological consequences of the heteromorphism. Achenes were classified into three types based on morphology. Central, intermediate, and peripheral morphs, named for the positions occupied within the fruiting head, range in shape from long, thin—beaked achene with barbed awns (central) to short wide achenes without beaks or awns (peripheral). Considerable within— and between—population phenotypic variation in achene and head characteristics was documented. Field experiments using artificial dispersal agents showed that central achenes are the most likely to adhere to animals and that the proportion of a population's achenes presented for dispersal that adhere depends on the proportion of central achenes produced in the population and on the proportion of achenes with adhesive awns. Once achenes had reached the ground, mean and median secondary dispersal distances were short (@<20 cm). Central achenes lose innate dormancy earlier than peripheral achenes during the period between autumn achene production and the onset of the summer rainy season. Germination is inhibited by darkness, though darkness becomes less inhibitive at the onset of the germination season (earlier for central achenes). In the laboratory, peripheral achenes germinated over a slightly narrower range of temperatures than central achenes. Percent germination was greater for central than intermediate achenes, and for intermediate than peripheral achenes, in two natural germination events in the field. Seed bank samples indicated that few if any achenes remain dormant between years. No significant differences in the growth rates of young seedlings were found in the greenhouse. A demographic experiment documented trade—offs resulting from the dormancy differences: central achenes tended to germinate earlier than intermediate and peripheral ones, and early germination resulted in greater mortality, but survivors that had germinated earlier attained greater size and produced more seeds. Intermediate achenes, while intermediate in all components of fitness, had the highest total fitness. This was because they resembled peripheral achenes in germinating late and having high survival, but they resembled central achenes in having higher percent germination. The results of these experiments suggest that a achene behavior ranges from "low—risk" (peripheral achenes) to "high—risk" (central achenes) within the progeny of a single individual, while individuals and populations vary in the proportion of offspring exhibiting each type of behavior.

Clonal variation in the effects of nitrogen application on growth and propagule production of arrowhead, Sagittaria trifolia L.

This study was conducted to determine the variation of growth and propagule production in the response of 19 clones of Sagittaria trifolia L., collected from six locations in southern Kyoto Prefecture, to four levels of nitrogen application (0, 8, 16 and 32kg/10a). Clonal variation was found in the nitrogen response to plant growth. Both sexual reproduction by achenes and vegetative reproduction by tubers increased with the increase in plant growth. The pattern of increase differed among the clones. The nitrogen response pattern differed according to the characteristics mentioned above. The increasing extent of sexual reproduction was higher than that of the vegetative one.The relationship between dry weight of the heaviest tuber and the number of tubers per ramet differed extensively among the clones. The nitrogen response of this relationship also differed. Of the 19 clones, 7 increased only in number, while 12 increased in both number and dry weight of the heaviest tuber. Although the heaviest tuber weight differed among the nitrogen levels, except in the case of two clones showing poor growth at 32N, the different nitrogen levels scarcely affected the frequency distribution of tuber weight.Based on the four characteristics of plant length, achene production, tuber production and the relationship between dry weight of the heaviest tuber and the number of tubers per ramet, the 19 clones were divided into four patterns. Intra-locational variation of these patterns was recognized in three of the six locations examined.

Effects of Temperature and Photoperiod on Common Crupina (Crupina vulgaris)

Achene germination of common crupina (Crupina vulgarisCass. ♯ CJNVU) was 86% or greater at day/night temperatures ranging from 15/4 to 29/25 C. Germination was greatly reduced at a day temperature of 36 C, regardless of the night temperature. The time required for maximum germination (9 to 19 days) increased with decreasing night temperature. Maximum leaf area, rosette diameter, and dry-matter accumulation during vegetative growth occurred at 22/18 to 29/25 C, 22/18 C, and 22/18 C, respectively. The plants attained 50% or more of maximum dry-matter accumulation at day/night temperatures ranging from as low as 22/4 and 15/11 C to as high as 36/25 C. Net assimilation rate was relatively insensitive to growth temperature. Rosettes of common crupina grown at 22/11 or 29/18 C exhibited almost complete photosynthetic and respiratory temperature acclimation. Increasing the photoperiod from 10 to 12, 14, or 16 h accelerated flowering. Maximum achene production occurred in the 16-h photoperiod, but viable achenes were produced in all photoperiods. Temperature during vegetative growth influenced subsequent responses to photoperiod. Plants grown for 83 days in a 14-h photoperiod at 15/4 or 22/11 C and transferred to 26/20 C flowered and produced seed in photoperiods of 8 or 16 h. Plants grown at 29/18 or 36/25 C subsequently flowered only in the 16-h photoperiod at 26/20 C. Common crupina has a wide tolerance of variations in temperature and photoperiod. Its range in the United States can be expected to continue to increase.

The consequences of predation in the population biology of the monocarpic species Cirsium palustre and Cirsium vulgare.

Predation by rabbits, Cheilosia grossa and especially Epiblema scutulana considerably reduces achene production in Cirsium palustre and Cirsium vulgare. In both species larger plants in a population are more frequently attacked, however the effect of predation is greater in medium sized plants. As a result the contribution of larger plants to the total achene production of the population is increased.In Cirsium vulgare larger populations are more susceptible to attack. The pattern and consequences of predation are discussed in relation to the occurrence in temporary habitats and to selectional processes. Predation intensifies existing developments in the population biology of these species. To compare the effect of predation for both species, detailed information of their population biology is necessary. At the moment the outcome of the comparison can only be indicated.

The role of pollination in the population biology of the monocarpic species Cirsium palustre and Cirsium vulgare.

The absence of cross-pollination in Cirsium palustre and Cirsium vulgare resulted in reduced achene production while the achenes produced were heavier than those produced after cross-pollimation. Establishment of plants from non-cross-pollinated achenes is comparatively higher, facilitating the founding of a population from isolated individuals in these wind-dispersed species.If achene weight is the result of a balance between cross-pollination and self-pollination (and/or apomixis), the first causing more and thereby lighter achenes to develop, increasing density of flowering individuals in a population may lower achene weight and consequently seedling survival. This may account for the frequently observed decline of populations of fugitive monocarpic perennials.

INTERGENERIC HYBRIDIZATION, INDUCED POLYPLOIDY, AND THE ORIGIN OF THE HAWAIIAN ENDEMIC LIPOCHAETA FROM WEDELIA (COMPOSITAE)

The genetic relationships of the Hawaiian endemic genus Lipochaeta and the nearly cosmopolitan but extra‐Hawaiian genus Wedelia were assessed by way of experimental hybridization. Hybrids between Wedelia biflora and diploid species of Lipochaeta consistently exhibited 15 pairs of chromosomes at meiosis, whereas the modal and maximum configuration seen in hybrids between W. biflora and tetraploid species of Lipochaeta was 15II + 11I. Meiotic pairing in microsporocytes of the intergeneric hybrid combinations involving Wedelia trilobata and both sections of Lipochaeta is lower than in intergeneric hybrids involving W. biflora. All of the intergeneric F, hybrids produced had relatively low pollen stainabilities ranging from less than 1–16% and, although they were vegetatively vigorous, they failed to produce viable achenes. The effects of chromosome doubling by colchicine in one species and several hybrids in Lipochaeta and in one intergeneric hybrid between Lipochaeta and Wedelia were studied. Chromosome doubling of the diploid species caused a decrease in pollen stainability and resulted in lack of achene production, whereas doubling the chromosomes of sterile intersectional and intergeneric hybrids restored female fertility and effected a dramatic increase in pollen stainability. Cytological analysis of the microsporocytes at diakinesis and metaphase I revealed pairs and quadrivalents in the induced polyploids. Pollen measurements indicated that pollen size in Lipochaeta is correlated with doubling of the chromosomes. Statistical analyses revealed that there is no significant difference in pollen size between the diploids and natural tetraploids, whereas both groups have pollen grains that are significantly smaller than the induced autotetraploid, the intergeneric allotetraploid, and the intersectional allohexaploid. The cytogenetic evidence indicates a relatively close genetic relationship between Wedelia and Lipochaeta and supports the view that the ancestry of the diploid section Aphanopappus of Lipochaeta (n = 15) is to be found in a species akin to Wedelia biflora (n = 15) and that this or a similar 15‐paired wedelioid species and an unknown 11‐paired wedelioid taxon are involved in the alloploid hybrid origin of the tetraploid section Lipochaeta (n = 26) of Lipochaeta.

Germination, establishment, and spread ofSoliva valdiviana(Compositae)

Abstract Achene production in So/iva occurs from mid November until the end of January but germination in the field is usually delayed until the first heavy rain in autumn. Two species of Soliva, S. valdiviana and S. pterosperma, occupy very similar ecological niches. Both species have a prostrate growth form which enables them to compete successfully with perennial lawn grasses in close-cut turf. Laboratory studies showed that whereas achenes produced early in the season take a long time to germinate, those produced later germinate rapidly. This feature is particularly marked in S. valdiviana. Germination is also greatly stimulated by light. About 40 days elapse from the first readily observable signs of capitulum formation to mature achene production in S. valdiviana. A central capitulum is produced first and under favourable circumstances capitula will subsequently develop on the laterals. Achenes will mature on detached capitula if given sufficient moisture and light. Presumably summer conditions in A...

Germination, reproduction and interference in the amphicarpic annual Emex spinosa (L.) Campd.

A comparison was made of the dimorphic subterranean and aerial achenes of the annual Emex spinosa (L.) Campd. Subterranean achenes were less dormant, had a higher percentage of viability, germinated at a faster rate, were less temperature-dependent in germination and produced larger seedlings than aerial achenes. Subterranean achenes germinated, equally well in light or dark but aerial achenes had a strong light requirement. There was a linear relationship between numbers of weight of aerial achenes and plant size in the field. More resources were allocated to reproduction in plants restricted in size because of environmental conditions. Subterranean achene production was less affected than aerial by density, nitrogen levels, varying field conditions and interference between plants grown, from subterranean and aerial achenes. In mixtures of such plants, those from subterranean achenes had larger leaf area and stems and more aerial achenes. These differences were not apparent in monocultures by the time of harvest. Seed dimorphism is more likely in short-lived fugitive species and the different roles associated with dimorphism (persistence in situ versus dispersal in E. spinosa) are seen as an ecological advantage in such species.

The effects of vegetation development upon achene production in the woody weed, groundsel bush (Baccharis halimifolia L.)

An examination of the achene production of groundsel bush (Baccharis halimifolia L.) populations growing within two exotic softwood stands of differing ages revealed that substantial reductions in this variable occurred following canopy closure. Mean reproductive efficiency, estimated as the number of achenes per gram dry weight of understorey bushes within the older stand, was only 31% of the corresponding value for bushes growing within a stand prior to the occurrence of canopy closure. Only small differences were found in both cumulative germination percentage and germination rate of achenes collected from each population. Female bushes, when shaded to a level of 14% open sky radiation, demonstrated a 30% reduction in the number of flowers initiated per head and a 25% reduction in percentage achene fill. Floral initiation was found to be independent of the production of oil reserves. Whilst dramatic reductions in the achene production of understorey individuals occur with plantation development, it is suggested that the density of unmanipulated populations of B. halimifolia may prevent the invasion and development of dominance by native tree species.

Achene production, dispersal, seed germination, and seedling establishment of Hieracium aurantiacum in an abandoned field community

Achene dispersal, seed germination, and seedling establishment of Hieracium aurantiacum L. were studied in an 18-year-old abandoned field community. Sexual reproductive output from selected patches declined rapidly after anthesis early in the season. The decrease in the number of achenes produced per head indicated a decline in reproductive output as the season progressed. Most of the achenes collected were deposited within 1 m of the source path. Achenes deposited near the source were larger and had a higher percentage viability than those deposited up to 3 m from the source. Seedling survival was higher within the parent patch compared with that at 5 dm in the adjacent herbaceous vegetation. Germination of the seeds gathered earlier in the season was higher than that of seeds gathered at monthly intervals as the season progressed. Cold treatment enhanced germination of seed produced late in the season but had little effect on seed produced early in the season.

Population Dynamics of Green Rabbitbrush in Disturbed Big Sagebrush Communities

Highlight: We investigated the dynamics of green rabbitbrush populations in relation to burning, livestock grazing, and chemical shrub-control as a range-improvement practice in big sagebrush communities. Green rabbitbrush plants sprout from roots, and density increases by seedling establishment after a fire. Achene production and seedling establishment are paramount to dominance by rabbitbrush after burning of big sagebrush communities. Rabbitbrush continues to dominate and periodically reestablishes itself for at least 15 years. Reduced populations of rabbitbrush persist in communities where dominant big sagebrush plants are 40 to 50 years old. Partial reduction in big sagebrush or rabbitbrush populations by applications of 2,4-D results in a large increase in seedling establishment of both species. When these communities are not disturbed or when all shrubs are removed, no shrub seedlings are established.

Control and Ecological Studies of Scotch Thistle

The range weed, Scotch thistle (Onopordum acanthium L.), is an increasing problem in the western United States. It competes with desirable forage plants and the flower stalks are a barrier to livestock movement. Prolific production of viable but dormant achenes makes this species a persistent pest. Applications of 4-amino-3,5,6-trichloropicolinic acid (picloram) in the spring or fall, at rates as low as 0.03 lb/A, gave control of Scotch thistle.