Proportion Of Shoots Research Articles

Ultra-brief training in cognitive reappraisal or mindfulness reduces anxiety and improves motor performance efficiency under stress

ABSTRACT Background and Objectives We examined the effects of ultra-brief training in mindfulness and cognitive reappraisal on affective response and performance under stress. We hypothesized that one or both types of training would decrease affective responding and improve performance, and that these effects might be moderated by acute stress induction. Design We manipulated training (mindfulness, cognitive reappraisal, control) between subjects and level of stress (low, high) within subjects in a 3 × 2 mixed factorial design. Method: Participants (N = 112, ages 18–35) completed two sessions on different days. In each session, they received mindfulness or cognitive reappraisal training or listened to a control script prior to a low- or high-stress simulated hostage situation. We measured motor performance efficiency (proportion of shots that hit hostile and hostage targets), affective responding (self-reported anxiety, salivary cortisol and alpha amylase, and autonomic physiology), and physical activity. Results Compared to control instructions, ultra-brief training in cognitive reappraisal or mindfulness reduced subjective anxiety and increased performance efficiency. There were few effects of training on other measures. Conclusion Ultra-brief training in cognitive reappraisal or mindfulness prior to a stressful task may be both helpful and harmful; effects are preliminary and subject to boundary conditions.

Peculiarities of <i>Hypericum perforatum</i> L. reproduction <i>in vitro</i> culture and development of plants in the open field

The possibility of using the method of cell and tissue culture for microclonal reproduction of St. Johns wort is shown. Direct morphogenesis was obtained using seedlings without roots at the age of 12 days. It was found that the introduction of BAP in a low concentration (0,1 mg/l) with IAA 1,0 mg/l into the MS nutrient medium promoted the minimum bud formation with the maximum yield of morphologically normal shoots without the need for an elongation phase. At the stage of rhizogenesis, the process of root formation was observed in all variants of the experiment; the proportion of shoots with roots was high and ranged from 88 to 90%. The maximum height of shoots, the number of pairs of leaves per shoot, and the length of plant roots were reached on the MS nutrient medium with IAA 1,0 mg/l. The period of adaptation to non-sterile conditions was 30 days, while a high yield of regenerant plants was observed. The survival rate of the adapted regenerant plants in field conditions was high (100%). Regenerant plants developed rapidly and bloomed in the first year. It was revealed that before planting in open ground, St. Johns wort plants propagated in vitro culture and passed the stage of adaptation to non-sterile conditions in containers with soil mixture formed a sufficiently developed root system from regenerant plants with a large number of adventitious roots 68 cm long. At the base of the shoot, from 2 to 5 renewal shoots 912 cm in height were formed. On the 65th day after transplanting, the number of renewal shoots more than doubled and averaged 7,8 pcs. per individual with a shoot height of 23 cm. In the third decade of August, the plants entered the budding phase, and on September 20, they entered the flowering phase. It was noted that by the beginning of flowering, the height of the plants increased to 4954 cm, and the diameter of the shoot up to 0,4 cm. From 16 to 24 pairs of oblong-ovoid standard leaves were formed on the plant. The formation of the floral part of the shoot (inflorescence) 2027 cm long began with the axils of 914 leaves and consisted of 710 pairs of lateral axes (paracladia). The average number of flowers was 82. The amplitude of variability of the main morphological traits of the shoot of the studied plants was at low and medium levels. It was found that the development of microclonally propagated plants by the end of the first growing season corresponded to the growth and development of St. Johns wort plants of the second year of life grown by seedlings.

Monitoring deer food and browsing in forests: Coherence and discrepancies between national and local inventories

Field-based monitoring of deer food availability and browsing on recruiting forest trees is a necessary but labour-intensive task. We explored how such estimates from a low-resolution multipurpose national forest inventory (NFI) (plot density 0.3 km−2) corresponded with estimates from local inventories that specifically and in greater detail monitor the availability of deer food and browsing intensity (LFI) (plot density 2–3 km−2).We used NFI and LFI data from 16 moose Alces alces ranges (mean area 276 ± SE 69 km2) in southern Norway. Only the height segment 30–130 cm of browsable trees could be obtained from the NFI data, while moose can browse trees from 30 to 300 cm in height. According to the LFI, the browse species did not have similar proportions of their browsable stems below 130 cm. Using only the stems from heights of 30–130 cm overestimated the availability of RAS (rowan, aspen and sallow) relative to birch (silver birch and downy birch) and Scots pine.The browsable biomass per stem of each species also varied between ranges, which introduces uncertainty to the food availability estimates that are based on stems only. Nevertheless, the NFI density of stems at 30–130 cm heights can be a useful index for species-specific comparisons of browse availability across ranges, because the variations between ranges in stem densities outweighed the biomass variations per stem. The NFI and LFI estimates of the species-specific densities of stems at 30–130 cm heights were significantly related and close to isometric (1:1), especially for RAS and pine.We did not find strong relationships between NFI and LFI in the browsing intensity (i.e. proportion of shoots that were browsed during the winter). The explained variation was only 11% (R2) for RAS (p = 0.281) and 32% for pine (p = 0.028). This was likely due to the small sample sizes of browsed trees in the NFI and methodological differences between the NFI and LFI in how browsing intensity is estimated. ConclusionsUsing data from national forest inventories can be an efficient but low-resolution way to monitor browse availability for deer, provided that the monitoring includes the full range of tree heights reachable for the deer (e.g., 30–300 cm for moose). It is also a prerequisite that the number of NFI plots is sufficient to cover the spatial variability of the area. Regarding browsing intensities, adjustments in both the NFI and LFI approaches are needed to make the two monitoring schemes more comparable.

Introducing the potential biological control agent Frateuria defendens into pot- and field-grown grapevines

Bois Noir is a major yellows disease in grapevine with no current means of control. The endophyte Frateuria defendens (Frd), isolated from the insect vector of Bois Noir, is a potential biocontrol agent for this disease. The aim of this study was to determine an efficient way to introduce Frd into mature vines under field conditions. Shoots of young and field-grown vines were sprayed with Frd suspension supplemented with either Tween 20, BB5, DX, or Triton X-100 as surfactants. The presence of Frd was confirmed by PCR in sprayed leaves, and in leaves below and above the sprayed site. The results showed that cells of Frd penetrate and move inside the vine shoots under field conditions. Highest penetration rate was achieved when leaves were sprayed with 108 or 109 colony forming units per mL (CFU mL-1) of Frd with addition of 0.1% Tween 20. The addition of a surfactant is essential to increase the proportion of shoots with Frd.

Sexual lability during an individual's life: the case of the sedge Carex secalina

Various environmental and physiological factors that affect sex expression in plants have been identified. We made the presumption that in perennials, age may be a key factor that significantly diversifies sex expression over consecutive years of an individual's life. To test this hypothesis, we chose the sedge Carex secalina, a plant that reproduces only sexually and exhibits different sex expression patterns. These patterns had been previously observed in natural populations. In a four‐year experiment, the sex of spikes formed on reproductive tillers of 100 individuals originating from three populations was monitored. A significant association between individuals’ age and number of female/male spikes was found for each population. In addition, significant differences between the populations in the ratio of shoots with bisexual spikes to shoots with unisexual spikes were revealed. We also showed that the proportion of shoots with bisexual spikes in the individual populations changed significantly with the age of an individual and that in the successive years of the individual's life, the production level of female and male structures changed. Moreover, an age‐dependent decrease in both the number and length of female and male spikes was observed.

The effect of interspecific hybridisation with Trifolium uniflorum on key white clover characteristics

A study was conducted to determine the effects of hybridisation with a wild relative, Trifolium uniflorum, on key morphological characteristics and N fixation of white clover (Trifolium repens). Overall, over 19 months under the conditions of the field environment used, dry matter (DM) production of the backcross 1 (BC1) generation was reduced compared with white clover, and did not increase with a second generation of backcrossing. The general morphological type of BC1 hybrids had a smaller leaf lamina area, shorter internodes and a more prostrate growth habit compared with white clover, which is likely to contribute to reduced DM production. Generally, lateral spread did not differ among BC1, backcross 2 (BC2) and white clover, except in spring when white clover had a wider spread than the hybrids. Hybridisation did not affect the proportion of shoot N derived from fixation, or shoot %N content. Fungal disease and virus symptoms were lower in the T. uniflorum parent than in white clover. This did not affect virus symptoms in the hybrids, and fungal disease scores were higher in BC1 than in the white clover parent. However, some hybrid families were more superior than others at maintaining (or improving) characteristics of their specific white clover parental cultivars, such as DM production, stolon density, growth habit, and resistance to shoot fungal diseases and viruses. This suggests it should be possible to develop elite hybrid breeding populations by recurrent selection of superior hybrid genotypes.

A new species of Stenodiplosis (Diptera: Cecidomyiidae) on florets of the invasive common reed (Phragmites australis) and its effects on seed production

AbstractA new species of gall midge, Stenodiplosis phragmicola Sinclair and Ahee (Diptera: Cecidomyiidae), is described. The host plant, Phragmites australis (Cavanilles) Trinius ex Steudel (Poaceae), is a tall, widely distributed emergent aquatic macrophyte. An introduced subspecies of the plant is considered invasive in North America (although a native subspecies also occurs). Insect specimens were collected during September 2010 and 2011 from the florets of common reed at 12 sites around Peterborough, Ontario, Canada. Preliminary data on ecological interactions between the plant and the insect are presented. Out of 2400 florets sampled, 9.5% were host to larvae of S. phragmicola. Three sites had much higher rates of infestation, with between 20% and 30% florets, and up to 100% of sampled shoots containing fly larvae. The largest stands in the sample all hosted fly populations and there was a positive association between the reproductive output of P. australis stands (measured as the average inflorescence mass per stand) and the proportion of shoots per stand containing larvae. The occurrence of S. phragmicola on the native subspecies of P. australis is also documented. Insects that consume reproductive structures of the common reed have not previously been reported from the plant's introduced range in North America.

Changes in the vegetative growth of the low-chill peach tree in response to reproductive shoot pruning after harvesting

The effect of reproductive shoot pruning (after harvesting) on the vegetative growth of peach trees was studied. After the harvest period, one group of plants was left unpruned; however, a second group of plants was pruned by heading back or thinning out their bearing shoots. Summer pruning improved the rejuvenation of wood and enhanced the growth of basal shoots thus increasing the proportion of shoots that arose on older wood or directly from the scaffold (+15%). Summer pruning was shown to affect branch regrowth, leaf restoration and radial expansion of the trunk; the leaf area removed was completely restored in 80 days by the increase of new branches (+108%) in the remaining shoots; however, the annual expansion of the trunk cross-sectional area was significantly reduced (−37.4%). Summer pruning also reduced the plant size from −7% to −26% and delayed autumn leaf fall (+10 days).

Exploitation of the sex pheromone of apple leaf midge Dasineura mali Kieffer (Diptera: Cecidomyiidae): Part 2. Use of sex pheromone traps for pest monitoring

Catches of apple leaf midge, Dasineura mali, in sex pheromone traps and subsequent galling damage to shoots over four successive midge generations per season were investigated during 2004 and 2005 in apple orchards in Kent, south eastern England, Trentino, northern Italy and South Island, New Zealand. The orchards were newly planted or established, had widely varying apple leaf midge populations and were subjected to different pesticide management regimes. The Julian date of the peak catch of midges in the sex pheromone traps increased approximately linearly with increasing generation number. There was also a strong increasing relationship between the Julian date of peak catch and increasing absolute value of latitude. A linear relationship was fitted within the range of 41 –51 degrees latitude included. Strong linear relationships on log-log transformed scales were found between the total and peak numbers of midges caught per generation and the populations of galls that developed subsequently. The best fit of log 10(total galls/ha) = 2.138 + log 10(total no. midges caught/generation) was obtained for the first and second generations. The relationship indicates that each male midge caught in a trap for a particular generation corresponds to approximately 137 galls being formed per hectare subsequently for that generation, providing that there are sufficient shoots and tender young leaves present to accommodate them. Clearly the proportion of shoots and leaves galled per hectare will depend on the numbers of shoots and leaves present in the particular orchard but knowledge of these parameters should allow simple estimates to be made. The regressions were significantly weakened when the third and especially the fourth generations were included, largely because of gall saturation or because tree growth had ceased. The relationships were not significantly affected by pesticide management regime, orchard age or country of location. In a further study, a good correspondence was found between pheromone trap catches and the percentage of shoots infested with eggs of D. mali for the first and second generation in an experimental orchard in Kent during 2006. The results indicate that the sex pheromone traps are effective for monitoring the flight activity of successive generations of D. mali, can be used to predict the severity of galling attacks to shoots and are likely to be useful for timing insecticide sprays.

FURTHER ANALYSIS OF THE MATCHING LAW TO DESCRIBE TWO‐ AND THREE‐POINT SHOT ALLOCATION BY PROFESSIONAL BASKETBALL PLAYERS

The matching law was used to analyze whether the proportion of shots taken from two- or three-point range would match the proportional reinforcement rates produced by those shots when the reinforcement rate of three-point shooting was changed. Rule changes in 1994 and 1997 altered the distance of the three-point line in the National Basketball Association, which created a quasiexperimental reversal design, thereby naturally changing three-point reinforcement rates. The present data partially confirmed predictions made by the matching law, in that increases in the relative rate of three-point shots attempted corresponded to increases in the relative rate of three-point shots made.

From controlled environments to field simulations: leaf area dynamics and photosynthesis of kiwifruit vines (Actinidia deliciosa).

Canopy leaf area development and daily rates of carbon acquisition of kiwifruit [Actinidia deliciosa (A.Chev.) C.F. Liang et A.R. Ferguson] vines growing in orchard conditions were modelled from mathematically-based physiological descriptions of leaf area expansion and photosynthesis of individual leaves Model drivers were temperatures and photon flux densities (PFD) measured in the orchard at 30-min intervals over the growing season. A modelling framework of shoot leaf area expansion, developed from controlled environment studies, was extended to whole vines by including canopy architectural components, such as shoot numbers, percentage budbreak and proportions of shoots in different length classes. Daily photosynthesis was modelled from rectangular hyperbolic functions determined for both sun and shade leaves and simulated from calculated light interception. Canopy leaf area, photosynthesis and PFDs within the canopy, obtained from measurements from vines grown in the orchard, were used to test the model. Close agreement occurred between the simulated and measured canopy leaf area development, and also between simulated and measured rates of photosynthesis. Total carbon acquisition over the growing season, estimated at 11 kg vine-1, compared closely with measured increments in vine biomass over the growing season. Results thus confirm the physiologically based model to be readily scalable to whole vines growing in orchard conditions.

Gibberellin-induced flowering in small tubers of Zantedeschia ‘Black Magic’

Small tubers (1.5 cm diameter) of Zantedeschia ‘Black Magic’ were used to study the induction of flowering by gibberellic acid (GA 3) and gibberellins 4+7 (GA 4+7). When planted these tubers remained vegetative unless treated with gibberellin. To control gibberellin dose, tubers were dipped into treatment solution (0–1000 mg l −1) for defined periods (0–16 h) and then rinsed with water to remove gibberellin from the tuber surface. The tubers were then planted and grown in a greenhouse. Flower emergence was recorded and plants were then dissected to determine whether initiation had occurred on non-flowering plants and whether axillary buds were vegetative or floral. No differences were found between responses to GA 3 or GA 4+7 treatments. The proportion of shoots that initiated inflorescences increased with an increase in both gibberellin concentration and/or treatment duration. Increased gibberellin dose also increased in the proportion of initiated flowers that subsequently emerged and the proportion of axillary buds that initiated flowers. Plants treated with high gibberellin doses also flowered earlier and with a lower leaf number. Our results indicate that high gibberellin doses induce more rapid floral initiation than lower doses. In addition to their role in floral initiation, gibberellins play a role in floral development. Uptake of gibberellin is shown to be primarily through the buds on the upper surface of the tuber.

Effect of time of cane initiation on subsequent fruitfulness in kiwifruit

The effects of time of cane initiation and the presence of fruit during cane development on production the following season was studied in kiwifruit (Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson ‘Hayward'). Canes initiated early in the season (before 1 December) were compared with those initiated late in the season (after 1 December). Early initiated canes (separated into those that carried/did not carry fruit during development), and late initiated canes were compared to separate the effects of time of initiation and the presence of fruit. There was no effect of time of cane initiation on budbreak or the proportion of shoots that flowered in the following season. Shoots that developed on early initiated canes were larger and more fruitful than those that developed on late initiated canes. Though late initiated canes produced a greater number of shoots than early initiated canes, the productivity of these shoots was lower, and so cane productivity (per unit length) was similar. Early initiated canes that carried fruit during their development were shorter and produced less fruit the following season than those canes that did not carry fruit during their development, but productivity per unit cane length was similar. Consequently kiwifruit growers should retain early initiated canes during winter pruning and optimise the number of buds laid down per square metre, ignoring their fruiting history.

Influence of soil mulching on winter chilling of kiwifruit

The influence of soil temperature during winter and early spring on subsequent budbreak and flowering of kiwifruit vines (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson ‘Hayward') was studied at three sites during a 2‐year period. Soil under kiwifruit vines was mulched for 28‐day periods by laying sheets of clear polythene under vines. Mulching in June or July increased soil temperatures at 0.1 m depth by 1–2°C compared to control vines, whereas mulching in August and September elevated soil temperatures by 3–6°C. Increases in soil temperature were directly proportional to the amount of solar radiation incident on the orchard (r 2=0.97). Mulching did not substantially alter the time of budbreak, the amount of budbreak, the rate of shoot growth, the number of flowers per shoot, or the number of flowers per winter bud. However, in one season the proportion of shoots that produced flowers was reduced when vines at the warmest site were mulched during late winter (August), but increased when vines at another warm site were mulched during early spring (September). These data suggest that the performance of kiwifruit vines is not very sensitive to soil temperature.

Rhizobium as a factor in the re-establishment of legume-based pastures on clay soils of the wheat belt of north-western New South Wales

Summary. Populations of Rhizobium meliloti in self-mulching clay soils (Vertisols) at 48 sites on 27 properties in north-western New South Wales were classified according to number and ability to fix nitrogen with several species of Medicago. Rhizobia were counted using serial dilution, nodulation frequency, plant infection tests. Abilities of the soil populations to fix nitrogen were determined in the laboratory with whole-soil inoculation of Medicago seedlings in test tubes with shoots exposed to the atmosphere and roots within the tubes under bacteriological control, and in the field using a technique based on the natural abundance of 15N in the soil. The majority of soils contained >1000 cells of R. meliloti per gram. The major component of those populations fixed nitrogen with lucerne (Medicago sativa) and some components of some soils also fixed nitrogen with M. polymorpha, M. scutellata, M. littoralis, M. tornata, M. laciniata and Trigonella suavissima. However, a number of soils were located which contained few if any rhizobia effective in nitrogen fixation with M. polymorpha. Overall, the effectiveness of nitrogen fixation of the naturally occurring populations of R. meliloti in association with M. polymorpha, M. scutellata, M. littoralis and M. tornata was only 46% of the effectiveness of standard strains. At one particular site, where 10 lines of annual Medicago spp. were growing experimentally, fixed nitrogen as a proportion of shoot nitrogen averaged only 28%. At that site, there were no effective rhizobia for M. scutellata and it was wholly dependent on the soil as the source of its nitrogen. The results are discussed in relation to the need for a substantial input of legume nitrogen for restoring the natural fertility of self-mulching clay soils in degraded wheat lands of north-western New South Wales. It is suggested that lucerne, or perhaps other perennial Medicago spp., might fill this role better than annual medics such as M. polymorpha and M. scutellata that are more dependent than lucerne on specific strains of R. meliloti to meet their requirements for symbiotic nitrogen fixation.

Settlement Rate of Lead Shot in Tundra Wetlands

Several species of breeding waterfowl have been shown to be exposed to lead shot on the Yukon-Kuskokwim (Y-K) Delta, Alaska. I seeded experimental plots with number 4 lead shot to determine the settlement rate of shot in wetland types commonly used by foraging waterfowl. I resampled plots for 3 years, using a suction dredge to remove sediment in 4-cm layers. There was no consistent change in the proportion of shot recovered in the 0-4-cm layer among years or habitat types. My results suggest lead shot is available to feeding waterfowl for many years, and that exposure of waterfowl to lead poisoning will likely occur for >3 years after the use of lead shot is curtailed.

Carbohydrate and Nitrogen Partitioning within One-year Shoots of Young Peach Trees Grown with Grass Competition

Carbohydrate and nitrogen were measured during 1992 and 1993 in shoots of peach [Prunus persica (L.) Batsch.] trees that were planted in 1989 and grown in three vegetation-free areas contained within plots planted to tall fescue (Festuca arundinacea Schreber), orchardgrass (Dactylis glomerata L.), or a mixture of Lolium perenne L. and Festuca rubra L. Trees grown in 9.3-, 3.3-, and 1.5-m2 vegetation-free areas had the greatest to the least fruit yield, respectively. Fruit number and mass were negatively correlated with stem mass. Grass type had little effect on mass, carbohydrate, or N partitioning within the tree. Individual sugars and carbohydrate partitioning were not affected by grass competition. In contrast, the proportion of shoot N partitioning into stem and leaves declined markedly as the size of the vegetation-free area increased. Proximity of peach trees to grass may have limited N uptake, which, in turn, reduced fruit yield but not stem and leaf growth.

Bud Respiration and Dormancy of Kiwifruit (Actinidia deliciosa)

Kiwifruit (Actinidia deliciosa(A. Chev.) C. F. Liang & A. R. Ferguson) is a perennial vine which requires winter chilling during the dormant period before it will flower and crop adequately. Quantifying the impact of winter temperatures is difficult because the first detectable responses of the vine are floral initiation and bud break which do not occur until spring. We believed that the respiration rate (RD) of buds of kiwifruit during the dormant period might provide an early indication of the changes in bud state associated with chilling. RDwas measured during autumn, winter and spring on buds collected from three contrasting regions of New Zealand.The RDof buds collected from these regions during the autumn were consistently different. Buds from the coolest region had the highest RD. These differences which were small, but consistent, were apparent by the time measurements started at the beginning of May. The autumn RDwas correlated with the proportion of floral shoots and numbers of flowers per winter bud, and to a lesser extent, the amount and spread of bud break. These correlations focus attention on the importance of this period in determining ‘winter’ chilling responses. It raises the possibility of RDbeing used as a predictor of vine performance as early as 17 weeks before bud break.A rapid increase in RDwas detected during spring. This occurred 3–6 weeks prior to bud break and coincided with developmental changes within the buds. Changes in RDin early spring were correlated with the timing and spread of bud break and the proportion of shoots that bore flowers, but not flower numbers. To provide a comparison of the potential use of RDas an index of vine response to chilling, bud break and flowering parameters were regressed against mean air temperature during the period from May to July. The correlations with air temperature were as useful as those based on the autumn or spring RDbut were available only 6–9 weeks before bud break. The autumn RDcan be obtained at least 8 weeks earlier than mean winter temperature data and this may be an important advantage if this information can be used for forecasting vine responses to chilling.

Temperature and Light Influence Growth and Flower Production in Heliconia `Golden Torch'

Flowering responses of Heliconia psittacorum L.f. × H. spathocircinata Aristeguieta `Golden Torch' to temperature and photosynthetic photon flux (PPF) were determined in controlled-environment conditions using a 2 × 2 factorial combination of temperature (32C day/20C night and 24C day/20C night) and PPF (475 and 710 μmol·m–2·s–1). Temperature had no significant effect on new shoot production, with an average of 9.3 shoots per plant being produced over the 248 days of treatment. More shoots, however, were produced at the higher PPF level (10.1 compared with 8.3 shoots). The proportion of shoots that initiated flowers (85%) was similar in all treatments. The duration from shoot until inflorescence emergence was significantly less at 32C day/20C night than at 24C day/20C night (140 and 146 days, respectively) and was unaffected by PPF. This duration also was significantly affected by the interacting effects of order of shoot appearance and the number of leaves subtending the inflorescence. The second shoots to emerge had the shortest duration from shoot emergence to inflorescence emergence. The number of leaves subtending the inflorescence increased at the higher temperature and decreased as shoot order increased but was unaffected by PPF. Temperature and PPF levels influenced total leaf area at flowering, with highest areas being achieved in the high temperature–low PPF combination. Acceptable flower quality with at least two, opened, well-formed, well-colored bracts was obtained in all treatments, although flower stems were taller and thicker at 32C day/20C night and these dimensions increased further with increasing order of shoot appearance. Stem diameters tended to be thinner at the lower PPF level. Overall, temperature was more dominant than light in influencing production and quality of flowers, but developmental factors associated with the order of shoot appearance also played a significant role. Flower production of `Golden Torch' should be feasible in temperature-controlled glasshouses in temperate regions where mean air temperatures can be maintained at ≈20C.

Seed production, germination rate, and seedling establishment ofScirpus pungens in tidal brackish marshes

We examined three components of sexual reproduction inScirpus pungens in order to explain the scarcity of seedlings in tidal brackish marshes of the St. Lawrence River estuary in Quebec. Six transects were established in three plant communities within two marshes. Seed production varied between 1 and 621/m2 among transects and increased with shoot density and the proportion of shoots with flowers. The number of seeds per fertile shoot did not vary among communities and averaged 1.8±0.1 (SE). The variation in seed production was related to the interacting effects of goose herbivory, soil type, and vegetative growth. The seed bank yielded 20–200 seedlings/m2 at different sites. Germination rates obtainedin situ under experimental conditions averaged 28% overall and reached 62% in one community with sandy substrate. Both the collection and seeding sites affected levels of germination. Seedlings varied between 0 and 25/m2 among sites and represented 0–3% of the total number of shoots. Low seedling survival was attributed to sediment accretion. Seedlings established themselves successfully only on bare patches created by erosion of the micro-bluff separating the lower and the upper marsh. We conclude that seeding ofS. pungens is not an effective technique to create or restore tidal marshes where sediment accretion is important.