Flowering Frequency Research Articles

The role of genetic mechanisms of sex determination in the survival of small populations of Silene littorea: A reintroduction experiment

Loss of genetic variation in populations may have other effects than inbreeding depression and loss of adaptive potential. In the case of the numerous gynodioecious plant species having cytonuclear systems of sex determination with dominant nuclear restorers of the male function, reduced genetic variation and increased inbreeding would increase the proportion of non-restorer recessive genes found in homozygosity, and therefore that of female plants producing pistillate flowers. This could have opposite effects on the extinction risk of the population. Female plants produce no pollen and may cause pollen limitation, but at the same time they may reduce average homozygosity and inbreeding depression because they are forced outcrossers. We observed that inbreeding indeed increased the frequency of female plants and pistillate flowers in the population, and that this effect was accompanied by reductions in population recruitment independent of inbreeding depression and likely due to pollen limitation. These results suggest that dominant nuclear restorers of pollen production speed up the extinction of small populations of Silene littorea, and that sex determination mechanisms might be an important factor to consider in the conservation of many plant species.

Patterns of seagrass (Posidonia oceanica) flowering in the Western Mediterranean

The intensive reconstructive sampling (1957–2004, 39 localities), a systematic direct observation (1992–2004, 1 locality) and particular direct observations (66 localities) of Posidonia oceanica meadows were analysed together with temporal series of flowering available in the literature (19 localities). This allowed the examination of temporal and spatial variability in annual flowering prevalence (FP, the fraction of meadows flowering in a given year) and of annual meadow flowering intensity (FI, number of inflorescences per shoot) for the period 1979–2004 across the Western Mediterranean, as well as spatial variability of flowering frequency (FF, the fraction of years that a given meadow has flowered) and shoot flowering probability (Pf, fraction of flowering stalks appeared per annual segment). Each year, on an average 17% of the investigated meadows flowered, ranging from 3 to 86% of meadows among the years. The highest annual FP and FI values were obtained in 2003 (FP=0.86 and mean FI=0.23±0.03 inflorescences shoot−1). A secondary peak of FP and mean FI occurred 9 years earlier, in 1994 (FP=0.44 and mean FI=0.08±0.02). Both peaks of flowering occurred after hot summers. Flowering synchrony in particular years across the Western Mediterranean and clines of increased meadow flowering frequency towards the North and East, suggests the existence of large-scale environmental mechanisms controlling the floral induction. On the other hand, meadow FF and Pf were highly heterogeneous among and within the meadows, indicating that local factors also may play a significant role in flowering induction. When flowering, the Western Mediterranean meadows showed an average 0.11±0.02 inflorescences shoot−1, but FI greatly varied among and along the series (from 0.002 to 0.54 inflorescences shoot−1) and decreased significantly with depth but was independent of meadow shoot density and meadow latitude or longitude. The shoot flowering probability was quite low (0.007±0.002 inflorescences shoot−1 year−1) and exponentially increased with shoot age.

Floral colour change in Pedicularis monbeigiana (Orobanchaceae)

We examined the effects of the retention of colour-changed flowers on long- and short-distance attractiveness of bumblebees and the likelihood of successive flower visits by bumblebees in Pedicularis monbeigiana. The lower lip changed colour with age from white to purple. Hand geitonogamous pollination significantly reduced seed production. No pollen limitation occurred in this species. Purple-phase flowers contributed minimally to pollinator attractiveness at long distance. The combination of less reproductive flowers with a lower amount of reward and floral colour change enabled plants to direct pollinators to reproductive, highly rewarding white flowers at close range. A high percentage of purple-phase flowers in an inflorescence was associated with a marked reduction in the frequency of successive flower visits to individual plants. We suggest floral colour change in P. monbeigiana may serve as a mechanism for enhancing inter-individual pollen transfer and reducing intra-individual pollen transfer.

(137) Cultivar Comparison of Heliconias for Use in Guam

Cultivars of heliconias were evaluated for use in Guam as a cut flower and in the landscape. Forty-five cultivars were planted at three locations in Guam. Due to insufficient plant material, the evaluation was preliminary. Noteworthy differences were observed among the cultivars. Differences were noted in time to establish, frequency of flowering, and resistance to wind damage. Establishment required large quantities of water. Once established, some cultivars appeared to be drought-tolerant; however, feral pigs and carabao became a problem due to massive mechanical damage. Typhoons also caused severe damage to the foliage. Rhizomes did not suffer obvious damage, resulting in recovery within 1 year. Heliconias as a cut flower does not appear feasible. As a landscape plant, heliconias should be given further consideration.

A demographic model explains life‐history variation in Arabis fecunda

Summary The distinction between semelparity and iteroparity is one of the most fundamental in life‐history biology. Despite an abundance of theory proposed to explain the evolution of this dichotomy, few quantitative empirical tests exist. We report here on life‐history variation in the perennial herb Arabis fecunda (Brassicaceae), in which differences in the frequency of iteroparity and terminal flowering (facultative semelparity) are expressed among populations. These differences are consistent over time, and a common garden experiment suggested that they may be at least partly genetically based. An analysis of demographic data over a 5‐year period from three populations indicated that a simple demographic model of life‐history evolution is consistent with life‐history variation in this species. Individuals in populations with greater mean adult survival were more likely to express iteroparity than individuals in populations with lower adult survival.

How does Dryobalanops aromatica supply carbohydrate resources for reproduction in a masting year?

The effect on reproduction of the dynamics of resource allocation was studied in an emergent and masting tree species, Dryobalanops aromatica (Dipterocarpaceae), in a lowland dipterocarp forest in Sarawak, Malaysia. Girdling of the reproductive shoots (5 mm diameter) caused an increase in abortion during the flowering period, but did not affect the fruit set at the middle or final stages of seed maturation. In contrast, 50% defoliation significantly affected fruit setting, but had little effect on flowering. The total leaf area of reproductive shoots was significantly correlated with final fruit set and total fruit mass. Control of the carbohydrate supply to reproductive shoots by girdling and defoliation made no difference to fruit size, but the fruit number was highly sensitive to carbohydrate availability. Total non-structural carbohydrate (TNC) decreased during the flowering period mainly in the branch (P<0.05), but fluctuated little in any organs during fruit maturation. Leaf nitrogen and photosynthetic capacity of the reproductive shoots were not significant variables for reproduction. Our results suggest that D. aromatica uses current photosynthates in the leaves of reproductive shoots as a carbon source during fruit development, but requires stored assimilates in the branch for flowering. However, since TNC was still present in all organs even after flowering, our study also suggests that storage of carbohydrate resources might not be the decisive factor in the occurrence or frequency of flowering in this species.

Plant species response to land use change –Campanula rotundifolia,Primula verisandRhinanthus minor

Land use change is a crucial driver behind species loss at the landscape scale. Hence, from a conservation perspective, species response to habitat degradation or improvement of habitat quality, is important to examine. By using indicator species it may be possible to monitor long‐term survival of local populations associated with land use change. In this study we examined three potential indicator (response) species for species richness and composition in Scandinavian semi‐natural grassland communities:Campanula rotundifolia,Primula verisandRhinanthus minor. With field inventories and experiments we examined their response to present land use, habitat degradation and improvement of local habitat quality. At the time scale examined,C. rotundifoliawas the only species responding to both habitat degradation and improvement of habitat quality. NeitherR. minornorP. verisresponded positively to habitat improvements although both responded rapidly to direct negative changes in habitat quality. Even thoughC. rotundifoliaresponded quickly to habitat degradation, it did not disappear completely from the sites. Instead, the population structure changed in terms of decreased population size and flowering frequency. It also showed an ability to form remnant populations which may increase resilience of local habitats. AlthoughP. verisand especiallyR. minorresponded rapidly to negative environmental changes and may be useful as early indicators of land use change, it is desirable that indicators respond to both degradation and improvement of habitat quality. Thus,C. rotundifoliais a better response species for monitoring effects of land use change and conservation measures, provided that both local and regional population dynamics are monitored over a long time period.

Effect of Temperature on Expression of Gynomonoecy in Selfed-seed Populations of Spinacia oleracea L.

For an efficient harvest of self-fertilized seeds in spinach, the effect of temperature on the expression of gynomonoecy was studied by employing selfed-seed populations from three gynomonoecious plants that produced 525, 359 and 186 seeds/plant. These selfed-seed populations were named P-1, P-2, and P-3, respectively. Seeds, sown monthly from December to March in an unheated glasshouse, revealed that the frequency of gynomonoecious plants was highest in P-1 and lowest in P-3 at any sowing time. In December-sown seeds of P-1, the frequency of gynomonoecious plants was 33%; as the sowing time was delayed, the frequency of gynomonoecious plants increased until it reached 100% in the March-sown seeds. Similar results were obtained in a growth chamber kept at 15, 20 and 25°C, and under 16 h photoperiod with 120 μmol · m−2 · s−1 PPFD. However, the frequency of hermaphroditic flowers on gynomonoecious plants was affected by temperature in all three populations; it was lowest at 15°C and highest at 20°C. At 25°C, hermaphroditic flowers occurred near the shoot apex, but the number of nodes with hermaphroditic flowers was equal or less than at 20°C due to the delay in bolting and/or reduced plant height. When seedlings were transferred to 25°C after bolting was induced at 20°C for 18 days, the mean plant height was reduced but the number of nodes with hermaphroditic flowers was unaffected. This cultural manipulation seems to be advantageous for seed production because it suggests that a line with a strong expression of gynomonoecy can be selected to maximize the production of self-fertilized spinach seeds.

A Pilot Scale Long-Term Experimental Study on the Effects of Grazing and Gap Creation on Burren Grassland Dynamics: Implications for Conservation

Burren grassland is an important habitat for biodiversity conservation, but studies to date have not provided sufficient scientific understanding of vegetation dynamics to inform selection of appropriate management prescriptions. This paper reports on a pilot scale study on a small grassland patch on limestone pavement near Mullach More in the Burren National Park. Through experimental manipulation, it examines the effects of grazing and bare soil gap creation on vegetation dynamics and reproductive success over six years, with a focus on temporal changes in cover, species richness, flowering rates, turnover and mobility. Cessation of grazing resulted in very marked frequency reductions for most species, but increases for some grasses and increased flowering frequency in some forb species. Gap creation resulted in vegetation change that persisted for at least two years under ungrazed treatment, but for six years in grazed sward. Soil depth decreased under grazing but increased under ungrazed treatment. The grassland patch had attributes suggestive of both equilibrium and non-equilibrium vegetation dynamics. As the small study area selected may not be fully representative of the markedly heterogeneous Burren landscape, this paper does not arrive at conclusions in relation to all Burren grasslands and their conservation, but rather identifies some attributes important in informing prescription selection that require further testing at larger scale.

Foraging preferences of Swift Parrots on Tasmanian Blue-gum: tree size, flowering frequency and flowering intensity

The Swift Parrot (Lathamus discolor), is a migratory species that forages primarily on Blue-gum (Eucalyptus globulus) during its Tasmanian breeding season. We investigated the foraging preferences of Swift Parrots for Blue-gum trees of different sizes and the effect of tree size on flowering frequency and flowering intensity over three seasons (1998, 1999, 2001). Swift Parrots showed a clear preference for larger Blue-gum trees: Blue-gum trees in which Swift Parrots foraged were ∼40% larger than surrounding (non-forage) trees, while the size-class distribution of forage trees was significantly skewed towards larger tree-size compared with surrounding non-forage trees. The mean flowering intensity of forage trees was also significantly greater than the mean flowering intensity of non-forage trees. Both flowering frequency and flowering intensity increased with tree size, although there was a trend for both flowering frequency and intensity to decline in the largest tree size-classes. Past clearing has resulted in the loss of over 50% of the original (pre-European) grassy Blue-gum forest in Tasmania. Remnant grassy Blue-gum forest as well as artificially planted Blue-gum trees typically occur in small patches of <1 ha, including many solitary and scattered trees in pasture, parkland and gardens. These isolated patches of Blue-gum frequently include trees of large stature, making them an important food resource for the endangered Swift Parrot.

Flowering frequency in a small population of Gymnadenia conopsea‐a five year study

This investigation evaluates the usage of genetic markers, microsatellites, to distinguish and re‐identify individual plants in a population of the orchid Gymnadenia conopsea. The study also illustrates the problem in estimating the size of a population from single year sampling as individuals can rest underground or occur in vegetative states; information extremely important for the understanding of population dynamics as well as providing information for conservation management. The total population size was, based on information from microsatellite loci, estimated to 84 individuals and vastly larger than the annual number of flowering plants (mean 31.4 individuals/year). Flowering frequency varied from 24–49%, 53 individuals flowered once, five individuals were flowering four years and a single individual was flowering five years. A common pattern was one or two flowering periods followed by a non‐flowering period. The observed number of alleles and the observed and expected heterozygosity varied among loci, although allele frequencies and genotype frequencies did not vary significantly among years.

Climate change effects on species interactions in an alpine plant community

Summary I examined the role of species interactions on the population dynamics of the herb Thalictrum alpinum and the sedge Carex vaginata by removing the dwarf shrub Dryas octopetala over four growing seasons at Finse, in the alpine region of south Norway, Furthermore, by increasing temperature (open top chambers) and nutrient availability (nutrient addition), I assessed the effects of climate warming on biotic interactions. Dryas removal increased the number of Thalictrum and Carex leaves, and flowering frequency of Carex. Flower stems and leaf stalks of Thalictrum, and the leaves of Carex, became significantly shorter following Dryas removal. Warming and nutrient addition increased vegetative plant growth, whereas warming alone had positive effects on sexual reproductive effort of the target species. My results suggest that there is both competition for nutrients, and a facilitative shelter effect of Dryas on its neighbours. Species interactions affected population dynamics of Thalictrum and Carex. Interactions between the impacts of Dryas removal and abiotic factors on leaf production, suggested that interactions between Dryas and neighbouring species might be modified if temperature and, in particular, nutrient availability increase under global warming. This study shows that both biotic interactions and abiotic environmental conditions may affect alpine plant population dynamics. Furthermore, it shows that climate change may modify species interactions. Species interaction effects should be included in climate change experiments and in future models predicting plant community changes under global warming.

Flowering phenology of tropical-alpine dwarf trees on Mount Kinabalu, Borneo

The flowering phenology of five alpine dwarf-tree species was observed in the summit region (3900–3950 m elevation) of Mt. Kinabalu on Borneo Island from March 1998 to November 2001. For each target species, 20–50 individual plants were numbered in two observation plots and the number of inflorescences was monitored at 2–3-mo intervals. The flowering patterns varied among species. Rhododendron buxifolium bloomed extensively every March–May at the main plot but the flowering pattern at the subplot was less predictable. Mass flowering occurred in March 1998 when drought stress was very severe due to an El Niño event. Rhododendron ericoides showed continuous flowering throughout the year and high synchrony between the plots. Extensive flowering of Leptospermum recurvum occurred synchronously within and between plots in the early half of 1999, then flowering activity decreased greatly. Photinia davidiana showed an annual flowering cycle but the timing of the peak flowering differed between the plots. Vaccinium stapfianum showed synchronous flowering between the plots and the flowering peak appeared at longer than 1-y intervals. Plant size was positively correlated with mean flower production in all species, and with the flowering frequency of R. ericoides, R. buxifolium, and V. stapfianum at one of the plots at least. Two fleshy-fruited species, P. davidiana and V. stapfianum, had high selfing ability for fruit production and showed relatively low flowering synchrony among individuals in comparison with the other species. These results indicate that the trigger for initiation of flowering may differ among sympatric species in a tropical-alpine ecosystem at least in normal years.

Patterns of size and fate relationships of contiguous organs in the apple (Malus domestica) crown.

• In apple (Malus domestica), the size of a shoot and the vegetative or reproductive fate of the terminal bud on that shoot are considered to be related phenomena but with contrasted results depending on studies. Our hypothesis was that these relationships would be partly cultivar-dependent. • Over a 3-yr period, the size relationships between shoots and fruit on two architecturally contrasted apple cultivars were assessed. For shoots, flowering frequency (dependent variable) was related to subtending shoot size (independent variable). • Linear correlations were adjusted for size relationships between contiguous shoots in the same year (inflorescence vs bourse-shoot), and between years with differences in slopes and intercepts between the two cultivars. The relationships between the size of a shoot and flowering frequency differed between the two cultivars, with high flowering whatever shoot size vs parabolic relationships between the two variables, respectively. • It is concluded that the relationships between shoot size and fate are cultivar-dependent. It is speculated that the flowering pattern not only depends on the property of the shoot alone, but also on the structural proportions of the parent branch and branching density.

Effects of harvesting and deer browsing on attributes of understory plants in northern hardwood forests, Upper Michigan, USA

Both forest harvesting and browsing by white-tailed deer ( Odocoileus virginianus Zimmerman) affect the composition and structure of forest vegetation throughout the eastern deciduous forest in the United States. We studied their affect and their interaction by measuring the composition, richness, cover, physical stature, and reproductive potential of vascular plants in the understory of three thinned (uneven-aged, even-aged, managing for old-growth characteristics) and two unthinned (second-growth, old-growth) forests dominated by sugar maple ( Acer saccharum Marsh.) in western Upper Michigan. Based on measurements taken five years after deer exclosures were established, we found consistent and strong statistical differences in species richness and percent cover related to forest harvest but not to deer browse. Percent cover of the understory vegetation showed weakly significant interactions between deer browse and forest harvest. Thinned forests had a greater average richness and cover of graminoid species, average cover of wild red raspberry ( Rubus strigosus L.) and sugar maple compared to unthinned forests. Measurements of plant morphology and the frequency of flowering and fruiting were more sensitive indicators of deer browse than community measurements such as richness and cover. Based on measures of physical stature and reproductive potential, sugar maple, red-berried elder ( Sambucus racemosa L.), bluebead-lily ( Clintonia borealis (Aiton) Raf.), small Solomon-seal ( Polygonatum pubescens (Willd.) Pursh.), false Solomon-seal ( Smilacina racemosa (L.) Desf.), rosy twisted stalk ( Streptopus roseus Michaux), and trillium species ( Trillium grandiflorum (Michaux) Salisb. and T. cernuum L.) all experienced significant browse damage. A better understanding of the interaction between forest harvest and deer browse and their effect on community composition and structure is critical to maintaining and enhancing biodiversity in managed northern hardwood forests.

Effects of simulated climate change on phenology and life history traits in Carex bigelowii

Climate change may have large effects on plants, especially in the Arctic. At two different sites, we studied the effects of enhanced temperature by using open‐top chambers (OTCs) on the clonal sedge Carex bigelowii, a common plant in arctic and alpine tundra. At the subarctic‐alpine site Latnjajaure, northern Sweden, overall flowering phenology was accelerated by open‐top chambers (OTCs) during the five years of treatment. For this protogynous population, male flower phenology accelerated more than female flower phenology, which resulted in an increased gender phase overlap. Sexual reproductive effort at the ramet‐level increased, both in male and female functions. Smut fungus incidence was not different among treatments, but a Dipteran seed predator attacked more ramets in the OTCs in one of five years. However, neither the fungus nor the seed predators affected plant growth or seed set measurably. Ramet‐level growth increased in the OTCs at Latnjajaure, but decreased in the OTCs at the maritime subarctic site Thingvellir, Iceland after three years of treatment. At Latnjajaure, the initial ramet‐ level responses were still evident after five years, while responses at the ramet population level disappeared: there was no difference in flowering frequency of ramets in the fifth year of the warming treatment. This is interpreted as either meristem limitation or internal resource depletion. At Thingvellir flowering frequency was unaffected by warming treatment, while ramet production decreased. Ramet production was unaffected by the treatment at Latnjajaure. These site differences in responses could be the consequences of differences in climate or site specific conditions. The trade‐off (negative correlation) between the number and size of vegetative offspring at Latnjajaure disappeared under enhanced temperatures (within the OTCs). This trade‐off was not apparent under the warmer conditions at Thingvellir.

Relationships among time, frequency, and duration of flowering in tropical rain forest trees

Flowering patterns are defined by the timing, duration, and frequency of flowering. Plants, particularly in the tropics, vary enormously with respect to these main variables of flowering. We used data from 302 tree species in a wet tropical forest to test a series of predictions regarding timing, duration, and frequency of flowering and examined the effect of each variable on the other two. Because timing, duration, and frequency of flowering can be constrained by phylogeny, we analyzed the data before and after considering phylogenetic effects at the level of family. Flowering activity peaked in the first wet season from May to July, refuting our prediction of peak flowering during the dry season. Our prediction that most species should flower several times a year was supported when species flowering more or less continually throughout the year were included in this category. Our prediction that supra-annually flowering species should be the least frequent was also supported with some qualifications. As we predicted, species flowering several times a year bloomed relatively briefly per flowering episode. Our prediction of shorter flowering duration for species flowering in the dry season and for those with a temporal separation between flowering and vegetative growth was also supported. Furthermore, supra-annually flowering species flowered for a shorter duration than annually flowering species and had a higher probability of flowering in the dry season compared to episodically or annually flowering species. Phylogeny significantly constrained variation in flowering frequency, but not in flowering time or duration, among confamilial species.

Ants in your plants: effects of nectar‐thieves on pollen fertility and seed‐siring capacity in the alpine wildflower, Polemonium viscosum

Flowers of the alpine skypilot, Polemonium viscosum, are attacked by nectar thieving ants of Formica neorufibarbus gelida. Ants exert selection on flower scent, size and shape in skypilots by damaging the pistils. Here, I report on the frequency and nature of contact between ants and pollen‐bearing anthers and determine the consequences of such contact for pollen performance and pollen donor paternity. In laboratory trials, ants entered flowers with full intact anthers and emasculated (female) flowers equivalently. Similarly, flower visitation rates of ants foraging naturally were not affected by the frequency of male phase flowers per plant. Ants actively interacted with the pollen‐bearing anthers during 21% of flower visits, on average. The rate at which such interactions occurred was predicted by the proportion of flowers in the male phase, under a random foraging model. The effect of ants on pollen fertility was tested experimentally by enclosing ants in male‐phase flowers on intact inflorescences. Adjacent control flowers were left un‐occupied. Pollen from flowers with a history of ant occupancy had significantly lower germination on virgin recipient stigmas than pollen from unoccupied control flowers. With hand‐pollination, sufficient pollen was transferred from ant‐occupied flowers to saturate seed set. However, a model based on the relationship between seed set and compatible pollen delivery by natural pollinators indicated that ant damage to pollen should reduce paternity accruing per flower visit by 20–26% on average, in nature. Results support the hypothesis that in P. viscosum, selection on floral traits by nectar‐thieving ants operates through male as well as female function.

Rain-forest fragmentation and the phenology of Amazonian tree communities

Habitat fragmentation affects the ecology of tropical rain forests in many ways, such as reducing species diversity of many taxa (Laurance et al. 2002, Lovejoy et al. 1986) and increasing rates of tree mortality and canopy-gap formation near forest edges (Laurance et al. 1997, 1998, 2001). Such obvious alterations have been documented in many fragmented forests, but more subtle changes, such as those affecting plant phenology (the timing and frequency of flower, fruit and leaf production), have received far less attention. Adler &amp; Kiepinski (2000) showed that different populations of the successional tree Spondias mombin on small man-made islands in Panama had highly synchronous flowering and fruiting. In montane forests in Colombia, Restrepo et al. (1999) demonstrated that under-storey fruit abundance was consistently increased over time near forest edges relative to forest interiors. Beyond these and a few other studies (Ackerly et al. 1990, Nason &amp; Hamrick 1997), however, the effects of fragmentation on plant phenology have been inadequately assessed, especially in the tropics.

Differential and reversible responses of common fen meadow species to abandonment

Abstract. We studied the effects of abandonment on two common fen plant species. In mown and a chronosequence of abandoned fen meadows spanning 35 yr, we measured fitness traits of the sedge Carex davalliana and the forb Succisa pratensis. Cessation of mowing had little effect on fitness traits and seed production of C. davalliana, but seedling density decreased more than threefold. Population density of S. pratensis decreased with increasing community biomass, but was not affected by the cessation of mowing. However, flowering frequency increased threefold and seed production was 20% higher in fallow meadows. Consequently, seedling density of S. pratensis increased nearly threefold after abandonment. However, these changes were not dependent on the age of the fallow. In a common garden and germination experiment, we found no differences in either species between plants from fallows and mown fen meadows, except for the height of the flowering stalk of S. pratensis. The combined results from the common garden experiment and the field studies indicate that changes in fitness traits observed in fallows were mostly phenotypic and likely to be reversible. If other species react in similar ways, there is a high potential for re‐establishing traditional fen meadow communities from fallows by mowing.