Showing papers on "Seedling published in 1995"

Effect of Inflorescence‐Feeding Insects on the Demography and Lifetime of a Native Plant

Abstract: The importance of herbivorous insects for plant demography and fitness is still controversial. The fact that their effect has not been fully evaluated within the context of the complete plant life cycle contributes to this controversy. This study is the first to test directly the influence of flower and seed consumption by a guild of inflorescence- feeding insects on the demography and fitness of a native plant over its whole life cycle within its natural environment. First, we discuss the evidence required to assess the effect of inflorescence-feeding insects on sequential stages in the plant life cycle. Then, we present the detailed results of two experiments that quantify the effect of inflorescence-feeding insects on seeds, seedlings, juveniles, and subsequent flowering progeny of Cirsium ca- nescens (Platte thistle), a native, monocarpic perennial species of Sandhills prairie, Ne- braska. Exclusion of inflorescence-feeding insects by insecticide had four main effects. Total seed output increased (P < 0.0005 in both experiments), indicating that resources were not limiting seed production. Flower heads produced later in the season contributed to the seed pool when insects were reduced (P < 0.01), suggesting that insect feeding restricted the phenology of flowering and pollination. The density of seedlings increased around plants protected from inflorescence-feeding insects (P < 0.0005), showing that safe sites were not limiting. Finally, the increase in seedlings led to higher numbers of flowering adults (P < 0.009), demonstrating that inflorescence-feeding insects significantly reduced lifetime fitness. Neither individual compensation for seed loss, nor density-dependent com- pensation for increased plant population densities, was observed when insects were ex- cluded. Thus, we conclude that the inflorescence-feeding insect herbivores limited seed production, seedling recruitment, plant density, and maternal fitness of this plant under natural conditions. This outcome challenges current theoretical models of the effect of insects on plant population dynamics. We predict that our result will be general for short- lived perennial plants with life histories in which persistence is tightly linked to regeneration from current seed, such as for fugitive perennials with transient seed banks.

Alternate bearing, predator satiation and seedling recruitment in Quercus robur L.

Abstract: 1 We investigated the relationship between seed production and seedling recruitment in Quercus robur in order to determine whether oak recruitment was seed-limited, herbivore-limited or microsite-limited. Over a 15-year period, Q. robur showed a pattern of alternate bearing, with significant (but not complete) synchrony between individual trees at several sites in south-east England. 2 Seedling recruitment was assessed in three ways: by annual destructive sampling, by monitoring permanent quadrats, and by ageing destructive samples of saplings using basal ring counts. 3 Seedling recruitment was closely correlated with the size of the acorn crop in some habitats but not others. In Sunningdale, where a competition-free seed bed was available every year and where seed predators were relatively scarce, oak seedlings appeared almost every year, and three peak densities of seedling recruitment followed three peaks of acorn production during the period 1985-92. In Silwood Park, where rabbits were abundant, there was little seedling recruitment except within rabbit exclosures and then only in years of peak acorn production. In Windsor Great Park, rabbit densities were lower and seedling recruitment was higher than at Silwood Park, but the association between seedling recruitment and acorn production could not be established with confidence because of imprecision in ageing the saplings. 4 Rates of acorn loss to invertebrate seed predators were broadly consistent with the hypothesis of predator satiation; low acorn crops suffered a higher percentage mortality than large acorn crops. The two principal acorn-feeding insects (the alien cynipid gall wasp Andricus quercuscalicis and the native weevil Curculio glandium) killed between 30% and 90% of the acorn crop in given years and between 0% and 100% of the acorn crop on individual trees. Vertebrate herbivores (principally rabbits and wood mice) destroyed most of the sound acorns in low years, removing experimentally placed acorns within 24 h. 5 The effectiveness of alternate bearing as a defence against short-lived, specialist insect herbivores and long-lived, generalist vertebrate herbivores is discussed. The evidence presently available does not allow us to discriminate between the competing hypotheses that alternate bearing is an evolved, antipredator strategy on the part of the oaks, or a constraint imposed by limited resource availability within the trees. 6 We conclude that the relationship between seed production and seedling recruitment in Quercus robur is variable from site to site: oak recruitment is seed-limited in open sites where vertebrate herbivores are scarce, microsite-limited beneath a dense forest canopy, but herbivore-limited in other sites, especially those where rabbits are abundant.

Competition vs. Facilitation of Tree Seedling Growth and Survival in Early Successional Communities

Abstract: Competition has been widely assumed to be one of the principal mechanisms underlying the resistance of shrub and herbaceous communities to invasion by trees. How- ever, there are potential mechanisms by which low-growing species, particularly in phys- ically stressful sites, could enhance growth or survival of tree seedlings (facilitation). The balance of inhibition and facilitation will determine the net effects of a community on tree seedling growth and survival. We conducted a large-scale field experiment to quantify the net effects of four major physiognomic types (shrub thickets, shrubby grass meadows, grass meadows, and herbaceous meadows) commonly found both in old fields and along utility rights-of-way on the growth and survival of three common tree species: sugar maple (Acer saccharum), red maple (Acer rubrum), and gray birch (Betula populifolia). The eight com- munity types were distributed in 23 sites representative of the range of upland environments present in the Hudson Valley of New York. Growth of planted seedlings of all three tree species was uniformly slow in all of the community types and environments. In all cases, the net effect of intact vegetation was to inhibit the growth of the tree seedlings. The intensity of competition varied substantially among the 23 sites but was not consistently related either to community type or to the biomass of the intact community. Instead, variation in the intensity of competition was related to the underlying favorability of the site for the growth of a particular target tree species. On physically unfavorable sites, tree seedlings grew slowly because of physical stress rather than competition with the intact vegetation. As site quality increased, the intensity of competition increased. Thus, competition and physical stress traded off along a site-quality gradient, with the result that tree seedling growth was uniformly slow. In contrast to the results for growth, there were cases in which the survival of these young tree seedlings was enhanced (facilitated) by the presence of intact vegetation. In particular, survival of the highly shade tolerant but drought intolerant sugar maple seedlings was facilitated by intact vegetation at many sites, especially for the 1988 cohort, which experienced a drought during its first growing season. Since we detected no consistent differences among communities in the intensity of competitive effects on seedling growth, the apparent differences among early successional communities in resis- tance to tree seedling establishment may be caused by variation in the duration of com- petition resulting from differences in height and canopy structure of the low-growing com- munities.

Forest Reorganization: A Case Study in an Old-Growth Forest Catastrophic Blowdown

Abstract: We studied the patterns and mechanisms of regeneration of a 400-ha wind- throw in an old-growth beech-hemlock forest caused by a tornado on 31 May 1985. Starting in 1986, and over a period of six growing seasons, we recorded percent cover and density of woody stems, and monitored seedling demography of nearly 5000 seedlings in the windthrow and adjacent forest. Plant community response to the disturbance was dramatic: by August of 1986, species richness, tree seedling density and total percent cover were significantly greater in the windthrow than in the adjacent forest. Shade-intolerant herbs (e.g., Erechtites hieracifolia) and shrubs (e.g., Rubus allegheniensis) established and rapidly increased in abundance during the first 3 yr, but began declining by the 5th yr of the study. Tree seedlings established in decreasing amounts through the 6 yr of the study, and the young tree canopy was dominated in 1991 by seedlings and sprouts that established prior to 1987. Fagus grandifolia, a shade-tolerant species that established via advanced regeneration, was dominant the first 3 yr, but was surpassed in the 5th yr by Betula alleghaniensis, a species of intermediate tolerance that established from seed germination just before or shortly after the disturbance. Tsuga canadensis seedling densities were initially high, but deer browsing prevented substantial growth and a drought in 1988 caused heavy mortality of browsed seedlings. Regeneration thus differed from the predictions of the gap and Hubbard Brook models of forest regeneration (which predict dominance by shade-intolerant species), and the severity model (which predicts dominance by shade-tolerant species). The differences point out important influences of availability of propagules and the impact of herbivory; and the need for more attention to models that incorporate multiple contingencies.

Evolutionarily Stable Seed Polymorphism and Small-Scale Spatial Variation in Seedling Density

Abstract: Using the evolutionarily stable strategy (ESS) approach in a model for the evolution of seed size, I show that small-scale spatial variation in seedling density favors the evolution of variation in seed size within individual plants if competition among seedlings is sufficiently asymmetric in favor of larger seeds. A single seed size is found to be never evolutionarily stable. I always find at least some continuous adaptive variation in seed size. The model generates the following predictions. At least some continuous variation in seed size is adaptive. Plants with many resources have more variable seeds than plants with few resources. Plants with low juvenile mortality have more variable seeds than plants with high juvenile mortality. Plants with aggregated seed dispersal have seed size distributions that are more biased toward small seeds compared to plants with more even seed dispersal. An explicit formula for the evolutionarily stable seed size distribution was obtained for Poisson-distributed seed nu...

Seedling recruitment patterns in a Belizean mangrove forest: effects of establishment ability and physico-chemical factors

Abstract: A field study was conducted to evaluate the relative importance of factors affecting seedling establishment and survival on a mangrove-dominated island in Belize. An examination of spatial patterns of seedling relative densities in relation to reproductive adults and physico-chemical conditions provided correlative information on factors affecting mangrove regeneration patterns. Distance from reproductive adults explained 89–94% of the variation in relative density of Rhizophora mangle seedlings, whereas availability of resources (light and NH4) explained 73–80% of variation in Avicennia germinans seedling relative density. Just after dispersal (December), 89% of the variation in Laguncularia racemosa seedling relative density was attributable to distance from reproductive adults, but 7 months later (July) 74% of the variation was explained by intensity of flooding- and salinity-related stresses. Survivorship (after 2.5 years) of propagules and seedlings of R. mangle and A. germinans transplanted to zones of contrasting physico-chemical conditions demonstrated that: (1) mortality was highest during the establishment phase and major causes were failure to strand before viability was lost, consumption by predators and desiccation; and (2) after establishment, differences in sensitivity to physicochemical stress factors such as flooding (A. germinans) and initial orientation of the seedling axis (R. mangle) exerted a further influence on seedling survival. The results indicate that seedling recruitment in these neotropical forests is strongly influenced by dispersal patterns, differential establishment abilities and effects of physico-chemical factors that vary with elevation and distance from the shoreline.

Thidiazuron-induced somatic embryogenesis in intact seedlings of peanut (Arachis hypogaea): Endogenous growth regulator levels and significance of cotyledons

Abstract: The regulatory role of thidiazuron (TDZ) and explant factors in imparting somatic embryogenic potential was assessed in relation to endogenous growth regulator levels in peanut (Arachis hypogaea L. cv. Tango). TDZ induced somatic embryogenesis over a range of concentrations (0.5 to 10 μM. Culture of seedlings for just 2 days on TDZ-supplemented medium was sufficient to induce somatic embryogenesis. Seedling age and retention or removal of cotyledons during culture influenced morphogenic potential significantly. The younger the seedlings, the better was the embryogenic response to TDZ treatment. The embryogenic potential of seedlings was limited for explants with no cotyledons and they did not respond to increasing levels of TDZ. In contrast, retention of at least one or both the cotyledons resulted in increased response to TDZ. Endogenous levels of cytokinins, auxins and abscisic acid were influenced by TDZ treatment, while TDZ itself was detected only in the cotyledons. The cytokinin N 6 -(2-iso-pentenyl)adenine (2iP) fluctuated on a 10-day cycle in the cotyledons ; TDZ treatment suppressed this change and caused an overall decrease in the pool of available 2iP in the tissue. It appeared that TDZ induced somatic embryogenesis in peanut by influencing endogenous levels of both auxin and cytokinins.

Salt tolerance of Hordeum and Brassica species during germination and early seedling growth

Abstract: Germination response and early seedling growth of barley (Hordeum vulgare L. 'Franklin', 'Harrington' and 'Abee'), wild barley (H. jubatum L.), canola (Brassica napus L. 'Excel') and wild mustard (B. kaber L. C. Wheeler) were investigated in iso-osmotic solutions of salts (NaCl, Na2SO4 + MgSO4) and polyethylene glycol (PEG) with osmotic potentials close to −0.9 MPa. Germination of Harrington and wild barley was reduced most by the non-penetrating solute PEG, suggesting that ion penetration might have reduced osmotic stress in the salt treatments. Wild barley was more salt tolerant than Harrington based on seedling growth relative to control plants. Of the three barley cultivars, Franklin was similar in salt tolerance to Harrington, while Abee was the most sensitive to all osmotica tested. Barley varieties had the lowest germination rate and poorest seedling growth in the PEG treatment. Compared with canola, wild mustard showed consistently greater tolerance to all osmotica during germination and early see...

A regulatory role for the ABI3 gene in the establishment of embryo maturation in Arabidopsis thaliana

Abstract: The ABI3 gene product of Arabidopsis is essential for correct completion of seed maturation. A severe mutant allele at this locus results in seed that remain green, fail to establish desiccation tolerance, and that germinate at a developmental stage when wild-type seed will not. Moreover, the formation of leaf primordia and xylem differentiation, both characteristic of germinating wild-type seedlings, can be observed in embryos harvested 12 days after flowering. Thus, mature abi3 embryos reach a developmental state that more closely resembles the character of a developing seedling rather than that of a dormant embryo. Previous studies of this gene have resulted in the suggestion that ABI3 is a transducer of abscisic acid induced seed dormancy. Our results demonstrate that the ABI3 gene product can be most accurately described as one of the major regulators of the transition between embryo maturation and early seedling development, rather than simply a transducer of the abscisic acid signal.

Acacia karroo invasion of grassland: environmental and biotic effects influencing seedling emergence and establishment.

Abstract: Acacia karroo Hayne is the most important woody invader of grassland in South Africa, and can greatly reduce the productivity of grassland A field experiment was conducted to test the hypotheses that emergence, growth and the 1st year's survival of Acacia karroo would be enhanced by (1) defoliation of the grass sward, (2) increased irradiance, (3) increased moisture availability and (4) its germination within cattle dung pats The study was conducted on one site above and one below the natural altitudinal treeline of this species in grassland of the eastern Cape, South Africa Not one seedling emerged from dung pats Neither location nor the other treatments affected the density of emerging seedlings, although only 404 seedlings m−2 emerged of the 200 seeds m−2 planted Shading dramatically increased the density of surviving seedlings In the open, only 3 and 15 seedlings m−2 remained respectively at the end of the growing season or the beginning of the next, compared to 233 and 195 seedlings m−2 under shading for these respective times This was attributed to the effect of shade on moisture availability in a season which received only 54% of average rainfall Seedling survival until the end of the growing season was enhanced (30%) by shade at both sites, but also by supplemental water (24%) and defoliation of the sward (7%) at the site above the treeline Across sites and treatments, seedling survival was related to moisture availability, with no or poor survival for < 500 mm rainfall, indicating this species can only establish in certain rainfall years Seedling survival over winter was not influenced by treatment, but was greater for larger seedlings Treatments affected seedling size, in particular seedlings growing under shade and within a dense grass canopy were etiolated A karroo seedlings are capable of establishing and surviving within a dense grass sward for at least a year, tolerant of low irradiance and of interference, which, because most seeds do not persist for much longer than a year, suggests this species forms predominantly a seedling bank This has implications for the invasion of grassland by woody species

Effects of mercury and cadmium on the activities of antioxidative enzymes in the seedlings of Phaseolus aureus

Abstract: Phaseolus aureus Roxb. was exposed to HgCl2 and Cd(NO3)2 either at the germination stage in concentration 0.5, 5 and 25 μM for 48 and 96 h, or at the seedling stage (5th day of germination) in concentration 0.5, 5 and 20 μM for 6, 24 and 48 h. The germination and the growth of roots (germination stage treatment) were less in Hg than in Cd treatment. The seedlings (seedling stage treatment) were, however, more susceptible to Cd than Hg. Both root and leaf tissues of the plant treated at the germination stage showed enhanced lipid peroxidation and activities of the antioxidative enzymes (catalase, guaiacol peroxidase and ascorbate peroxidase), except the catalase in leaf in 25 μM Cd treatment. At seedling stage the content of malondialdehyde increased significantly only in the leaf tissue, during 6 h exposure. The activities of all the enzymes exhibited an increasing trend in both the tissue of the seedlings, particularly the leaf, at least after 24 and 48 h, except the catalase whose activity declined in response to Cd. Active involvement of the guaiacol and ascorbate peroxidases, rather than catalase, in scavenging cellular H2O2 was indicated. It was concluded that the two metals had little primary damaging effect on membranes.

Seed Dispersal, Germination and Seedling Growth of six Helophyte Species in Relation to Water-Level Zonation

Abstract: SUMMARY 1. Seed dispersal, germination, and seedling growth characteristics of six helophyte species. Iris pseudacorus, Phalaris arundinacea, Phragmites australis, Typha angustifolia, T. latifolia and Scirpus lacustris, were investigated in relation to their water-level zonation. 2. The experiments demonstrated a large variation in these characteristics between the species. 3. Propagule floating capacities range from 1000 h (I. pseudacorus). 4. Seed germination in a water-level gradient revealed two groups with respect to germination percentage - exposed soil species (I. pseudacorus, Phalaris arundinacea, Phragmites australis) and submerged soil species (T. angustifolia, T. latifolia). 5. There were two contrasting types of seedling growth response to submergence and exposure: one group of species formed longest leaves under exposed conditions (Phalaris arundinacea, Phragmites australis, I. pseudacorus), and the other under submerged conditions (S. lacustris, T. latifolia, T. angustifolia). 6. The results suggest that early life-history characteristics of the species relate to their locations in the riparian zonation: Phalaris arundinacea and Iris pseudacorus at the higher end, Phragmites australis intermediate, and Typha spp. and Scirpus lacustris at the lower end. Species occurring at lower locations show adaptations to (periodical) flooding of the soil (submersed germination and growth), while those from higher locations require prolonged exposed soil conditions to germinate and to survive the establishment stage.

Mechanisms underlying the suppression of forb seedling emergence by grass (Poa pratensis) litter

Abstract: We investigated the mechanism by which grass litter (dead Poa pratensis L. shoots) suppressed the emergence of seedlings of four old-field forbs (Centaurea nigra L., Dipsacus sylvestris Huds., Hypericum perfioratum L., Verbascum thapsus L.) by determining the effect of litter on their seed germination and shoot extension. When seeds were placed beneath litter (715 g m -2 ) that had been collected from an old-field, the germination of all species except Verbascum was reduced significantly by 26% to 41% compared to a no-litter control. When seeds were placed in plastic dishes containing a leachate solution made from litter (7 g dish -1 ), the germination of two species (i.e. Centaurea and Dipsacus) was reduced significantly by 10% to 34% compared to the distilled water control. When germinated seeds were placed beneath litter, the emergence of seedlings of all species was reduced significantly by 95% to 100% compared to a no-litter control. These results indicate that grass litter may suppress forb seedling emergence by reducing seed germination and (or) by preventing shoot extension and that these effects are species dependent.

Spatial and temporal patterns in the emergence and survival of seedlings in arid Karoo shrubland

Abstract: 1. The influence of seed availability, weather and microsite on natural emergence and survival of seedlings was investigated over 38 months in arid shrubland in the southern Karoo, South Africa, developed under < 200 mm annual precipitation. 2. Small-scale clearing and herbivore exclusion experiments were conducted to test the hypotheses that seedling survival and growth were unaffected by competition and herbivory. 3. In undisturbed vegetation 20-800 seedlings m −2 emerged in the relatively cool and humid austral autumn. Densities of emerging seedlings were greater in microsites influenced by grazing, termitaria and plant litter than in undisturbed or exposed sites. The species composition of seedling assemblages resembled that of the vegetation. Survival varied from 5% in 1989 and 1990 to 25% in 1991, and appeared to be limited by the quantity of rain in winter and spring. 4. Vegetation clearing increased the amplitude of soil moisture oscillations at 50 mm below the soil surface, but reduced the rate of soil-moisture depletion at 150 mm below the surface. 5. The species composition of perennial seedlings in cleared vegetation was influenced by the original plant cover and the presence of plant litter on the soil surface. 6. Established plants had more influence on seedling survival than did grazing by wild animals or sheep. Proximity to mature perennials reduced both survival and growth of Karoo annuals and perennials. 7. Grazing by sheep and wild animals reduced the size, but not the survival, of perennial seedlings palatable to mammalian herbivores. Annual plants were larger and more abundant in clearings than in undisturbed shrubland

Ten-year seed bank and vegetation dynamics of a tidal freshwater marsh

Abstract: A decade-long examination was made of recruitment and establishment in a tidal freshwater high marsh along the Delaware River. Over the 10 yr of the study, seed bank, field seedlings, and vegetation showed variable patterns and significant year-to-year fluctuations. Patterns of each species were unique, perhaps the result of specific germination and/or establishment requirements and seedling morphology. For a given species there was little correlation among seed bank, seedling, and vegetation patterns, and germination success did not guarantee establishment. Species diversity showed significant year-to-year fluctuation, but there was no trend, and perennials did not change in importance during the 10-yr period. Because four annual species (Bidens laevis, Cuscuta gronovii, Impatiens capensis, and Polygonum arifolium) composed over 90% of the seed bank and field seedlings, and 58-89% (x = 70 ? 4) of the cover, community dynamics were dependent on seedling recruitment. For a given species life history stages (seed bank, field seedlings, and vegetation) were not predictable over the temporal scale of a decade. It is predicted, however, that if hydrology remains unchanged, the same suite of species will persist. The importance of the parasite Cuscuta gronovii is noteworthy.

The effect of seedling age on the likelihood of herbivory by the slug Deroceras reticulatum

Abstract: 1. The effect of seedling age on the risk of predation by molluscs was investigated for three common grassland species by exposing uneven-aged seedling assemblages (monoculture and mixed species) to grazing by the slug Derocerus reticulatum in experimental trays in greenhouse conditions. 2. In monoculture, seedling age was found to influence significantly the risk of mollusc attack on both Senecio jacobaea and Taraxacum offficinale. By contrast, the risk of attack on Veronica persica seedlings was unrelated to seedling age. 3. In a mixture of Taraxacum and Senecio seedlings, Taraxacum seedlings were not selected by slugs on the basis of age as they were in monoculture. Senecio seedlings in mixture with Taraxacum were generally grazed upon less than conspecifics in monoculture, although the effect of seedling age upon relative susceptibility to herbivory was broadly the same as in monoculture. 4. The results demonstrate that the timing of herbivory by molluscs can be crucial in determining the survivorship of a cohort of seedlings. The effects which seedling morphology, changes in seedling palatability with age, relative growth rates and pattern of association with neighbours have upon mollusc feeding behaviour are discussed, highlighting the role molluscs play as an important selective force in plant communities.

Disturbance, life history strategies, and seed fates in alpine herbfield communities.

Abstract: Species responses to disturbance are governed primarily by their life history and physiological traits and by the characteristics of the disturbance. Species reproductive traits are especially important in determining the potential of species to establish and to persist following disturbance. Herein, I review available literature on relationships among disturbance, species life histories, and seed fates in tundra environments. Research conducted on these relationships in alpine herbfield vegetation on the Beartooth Plateau, Montana, over the past 9 yr by my colleagues and myself is synthesized. In tundra environments, species reproductive capacities are often similar to those in more temperate environments, but short, cool growing seasons constrain seed production and reduce seedling growth and survival. Highly variable growing season conditions result in large differences in seed production and seedling establishment among years. On disturbed sites, disturbance characteristics determine the seed and seedling environment and influence rates of establishment. In these windy environments, relationships among soil surface characteristics and seed morphological attributes determine both the horizontal and vertical movement of seeds on exposed soils. Once seeds are incorporated into the soil, soil physical and chemical properties determine temperature and nutrient regimes and have the greatest effects on seed germination and seedling growth and survival. Examining the seed fates of herbfield species with varying life histories illustrates that the identities of species that establish following disturbance are largely predictable from their reproductive traits. Disturbance characteristics determine the success of different reproductive strategies and significantly influence community structure.

Natural Herbicide Potential of Alfalfa Residue on Selected Weed Species

Abstract: Alfalfa (Medicago sativa L.) contains water-soluble substances that are toxic to itself (autotoxicity) and to other species (allelopathy). Experiments were conducted to determine the potential of using alfalfa residue as a natural herbicide for inhibition of weed seed germination, seedling growth, and development. Various weed species were germinated in aqueous extracts from dried alfalfa using cold (5°C), warm (24°C), and hot (80°C) treatments. Results indicated that inhibition of weed seed germination was dependent on the aqueous extraction method, residue application rate (w/v or w/w), and weed species. The greatest inhibition of germination was 44%, when 60% (w/v) warm aqueous extract was applied to lambsquarters (Chenopodium album L.). Seedling growth was also inhibited by residue application at various rates. Root length was more inhibited than increase in shoot length. In terms of total seedling length, giant foxtail (Setaria faberii Herrm.) was the most resistant species and lambsquarters was the most susceptible among the weed species studied to alfalfa aqueous extracts. Weed seed germination percentage decreased as incubation time increased from 8, 16, 24, and 48 h. An alfalfa aqueous extract incubated for 48 h caused the greatest inhibition of velvetleaf (Abutilon theophrasti Medic.) seed germination (25%). When alfalfa residue was incorporated with silica sand, the growth and development of lambsquarters, pigweed (Amaranthus retroflexus L.), velvetleaf, and crabgrass [Digitaria sanguinalis (L.) Scop.], as measured by plant height, leaf area, and total, shoot, leaf, and root dry weight, were significantly inhibited as the rate increased from 0.0 to 2.0 g kg -1 . Dried alfalfa residue significantly stimulated plant height, leaf area, and total dry weight including shoot, leaf, and root of giant foxtail and cheatgrass (Bromus secalinus L.). Results suggest that alfalfa residue has a contrasting effect on weed growth and development due to water-soluble allelochemicals present in the residue.

Seed and Seedling Demography of Four Co‐Occurring Carpinus Species in a Temperate Deciduous Forest

Abstract: In order to clarify regeneration traits and their fitness, we compared seed fall, seedling emergence, and first-year seedling survival of four co-occurring species, Carpinus tschonoskii, C. japonica, C. laxifiora, and C. cordata, in an old-growth temperate deciduous forest in Ogawa Forest Reserve, central Japan. Seedling emergence ratio of C. cordata (5.5%), whose seeds mostly germinated 1.5 yr after seed fall, was lower than the other species (8.5-11.2%). First-year seedlings of Carpinus tschonoskii and C. japonica had much lower survival rates (2.7%, both species) than C. laxifiora and C. cordata (7.5- 8.5%) under closed canopy, suggesting that the former two are more disturbance dependent than the latter two. They are characterized by their seed and seedling performances as seed rain type fundamentally; however, C. cordata and C. laxiflora are able to establish a seedling bank, and C. cordata has a seed bank too. These regenerative strategies partly explain the abundance and population structure of the four species in this old-growth forest. Multiple regression analyses showed that topography was important for survival of all species but C. cordata. This result was consistent with the adult distribution of these species in this forest. Wind dispersal of Carpinus is effective, both to escape from density- or distance- dependent high mortality and to increase the chance of arriving at canopy gaps, where seedling survival rate is high. However, escaping high mortality seems relatively more important for C. laxifiora and C. cordata (seedling bank strategy), and arriving at a canopy gap is relatively more important for C. tschonoskii and C. japonica (seed rain strategy).

Seed stratification and germination strategy in the Mediterranean pines Pinus brutia and P. halepensis.

Abstract: The ecophysiology of germination in Pinus brutia and P. halepensis was studied in seeds collected from different areas of Greece. In regard to the temperature range of germination, both P. halepensis and the southern provenance (Lasithi, Crete) of the East Mediterranean pine, P. brutia, follow a typical Mediterranean pattern. In the latter species, dramatic differences in the degree of dormancy were noted among the three provenances investigated; in all seed lots however, 20°C was clearly the optimal temperature for germination. Stratification resulted in a considerable promotion of P. brutia seed germination. Nevertheless, the inductive effect of stratification was shown to differ among the three provenances used, escalating from a simple increase of germination rate (in the southern seed lot from Lasithi, Crete) through a broadening of the temperature range of germination (in the intermediate lot from Thasos Island) to, finally, a dramatic release from a particularly deep dormancy (in the northern lot from Soufli). These deeply dormant seeds of the latter provenance displayed an absolute stratification requirement; prolonged illumination or seed coat scarification could not substitute for the promotive effect of prechilling. A considerable interaction between far-red light and stratification was revealed in the dormant seeds of P. brutia (Soufli provenance); far-red pulses during stratification could either cancel or diminish the germination promotion induced by low temperatures. The differences observed in the germination behaviour among the various P. brutia provenances may be attributed to a variable ecophysiological strategy in regard to the temporal pattern of seedling emergence and establishment. According to the variants of this strategy, seed germination is timed to occur during either spring (in regions with relatively cold and moist climates), or autumn and early winter (in southern, mild and dry areas) or both (in intermediate conditions).

External and internal root colonization of lodgepole pine seedlings by two growth-promoting Bacillus strains originated from different root microsites

Abstract: Root colonization and in vitro carbon substrate utilization by two seedling growth-promoting Bacillus strains that originated from different root microsites were studied in greenhouse and growth chamber experiments. Strain L6, identified as Bacillus polymyxa, was previously isolated from rhizosphere soil containing roots of pasture plants, and Pw-2, tentatively identified also as B. polymyxa, was isolated from within surface-sterilized lodgepole pine (Pinus contorta var. latifolia (Dougl.) Engelm.) roots. Rifamycin-resistant strains derived spontaneously from wild-type strains L6 and Pw-2, designated strain L6-16R and Pw-2R, respectively, were used to monitor lodgepole pine root colonization in a closed tube assay system. Three-week-old pine seedlings were inoculated with 105 colony-forming units (cfu) of strain Pw-2R or 106 cfu of strain L6-16R, and external and internal root colonization was assessed 2 and 4 weeks later. Strains L6-16R and Pw-2R were both recovered from pine rhizosphere samples with > 5...

Ecophysiology of germination in the aromatic plants thyme, savory and oregano (Labiatae)

Abstract: Ecophysiological aspects of seed germination were investigated in the widely distributed Mediterranean-endemic, aromatic plants thyme (Coridothymus capitatus), savory (Satureja thymbra) and oregano {Origanum vulgare subsp. hirtum). Thyme seed germination is light indifferent, whereas oregano seeds have an absolute light requirement; their germination can be promoted even by green safelight or far-red light. In savory, a portion of the seeds germinates in the dark and germination can be either increased or decreased by the appropriate illumination. All three species show more germination at a relatively low temperature range, a Mediterranean characteristic, with an optimum around 15-20°C. The rate of germination is considerably higher in the tiny seeds of thyme and oregano than in the larger seeds of savory. In the latter species, germination is also dependent upon the age of the seeds; old seeds germinate to a higher percentage than fresh ones, as already observed by Theophrastus, possibly as a result of the volatilization of the essential oils present on the nutlet coat. Seeds of thyme, savory and oregano are dispersed within the persistent fruiting calyces and the seeds eventually germinate within it. Essential oils in the calyx strongly inhibit germination of the enclosed seeds; germination is much suppressed in thyme and to a lesser extent in savory and oregano. This diaspore dormancy caused by essential oils apparently is overcome under natural conditions by leaching of the inhibitors with rainwater. It is suggested that this dormancy operates as an adaptation strategy that delays germination by acting as a rain gauge. In this way, seed germination and subsequent seedling

Soil protozoa and forest tree growth: non-nutritional effects and interaction with mycorrhizae

Abstract: Mycorrhizal (Lactarius rufus Fr.) and non-mycorrhizal Norway spruce seedlings (Picea abies Karst.) were grown in a sand culture and inoculated with protozoa (naked amoebae and flagellates) extracted from native forest soil or with protozoa grown on agar cultures. A soil suspension from which the protozoa were eliminated by filtration or chloroform fumigation was used as a control. After 19 weeks of growth in a climate chamber at 20–22°C, the seedlings were harvested. Protozoa reduced the number of bacterial colony-forming units extracted from the rhizoplane of both non-mycorrhizal and mycorrhizal seedlings and significantly increased seedling growth. However, concentrations of mineral nutrients in needles were not increased in seedlings with protozoan treatment. It is concluded that the increased growth of seedling was not caused by nutrients released during amoebal grazing on rhizosphere micro-organisms. The protozoa presumably affected plant physiological processes, either directly, via production of phytohormones, or indirectly, via modification of the structure and performance of the rhizosphere microflora and their impact on plant growth. Mycorrhizal colonization significantly increased the abundance of naked amoebae at the rhizoplane. Our observations indicate that protozoa in the rhizosphere interact significantly with mycorrhizae.

Relationships between Seed Fates and Seedling Establishment in an Alpine Ecosystem

Abstract: On exposed soils relationships between soil surface characteristics and seed morphological attributes often determine the microsites of seed entrapment and influence patterns of seedling establishment. I examined seed and seedling fates of alpine species with varying morphology over a range of uniform- and mixed-particle-size soils on the Beartooth Plateau, Montana. Physical relationships between seeds and surface soils deter- mined entrapment and retention within the zone of potential emergence (0-1 cm depth). Seed size (length or mass), the presence or absence of specialized appendages or seed coats, and the nature of the appendage or seed coat influenced numbers of seeds trapped and seed distributions among the particle sizes. Antrorse hairs, hygroscopic awns, pappuses, and mucilaginous seed coats all resulted in higher entrapment over the range of particle sizes. The effectiveness of different seed morphologies was decreased by prolonged exposure (1 yr) to the environment. In contrast to seed entrapment and retention, seedling emergence and survival depended on the ability of the different particle-size soils to meet the biological requirements of the species. Although some seedling emergence occurred in particle sizes that ranged from <0.5 to 4-8 mm, almost no seedlings survived in particle sizes larger than 1-2 mm. In particle sizes in which emergence occurred, a higher percentage of the total seeds trapped survived the first growing season as seedlings for large-seeded than for small-seeded species. For most species, the highest entrapment and retention occurred in particle sizes in which there was little or no emergence. Seedling emergence and survival were related to seed entrapment only for species with reasonably high emergence, and the R2 values were often low. Understanding seedling establishment patterns in different-par- ticle-size soils requires knowledge of how relationships between seed morphology and soil characteristics affect entrapment patterns, and knowledge of soil particle size thresholds for seedling establishment.

Seed fate in a tropical mistletoe : the importance of host twig size

Abstract: 1. In a bird-dispersed neotropical mistletoe two aspects of seed deposition are hypothesized to influence seedling establishment on host trees: the size of the host stem on which seeds are deposited and whether seeds are deposited singly or in small groups. 2. In Monteverde, Costa Rica, seeds of Phoradendron robustissimum (Viscaceae) were planted on 10 host trees (Sapium oligoneuron; Euphorbiaceae) and seedling establishment was followed for 3 years. 3. Seed clumping (groups of five vs single seeds) had no effect but stem size had a strong effect on seed persistence and seedling establishment. 4. Seedling establishment was most frequent on twigs in the 10-14mm diameter class; however, at least one seedling established on all but the largest (>80 mm diameter) of seven size classes of stems used in the experiment. 5. Causes of seed loss and seedling mortality showed directional patterns across the range of stem sizes; small twigs died frequently, leading to death of seedlings on them, whereas germinated seeds often died in situ on large branches, apparently unable to penetrate the thick bark of the host tree. 6. In the smallest two size classes of host stems (<10 mm diameter), twigs with mistletoe seeds died more frequently than those without mistletoe seeds, suggesting that mistletoe seeds can induce death of small host twigs. 7. Many seeds disappeared shortly after being planted and an exclusion experiment suggested that missing seeds may have been eaten by arboreal seed predators. 8. Thus, the size of twigs on which mistletoe seeds were deposited strongly influenced seed fate

Seedling distribution and potential persistence of the exotic shrub Lonicera maackii in fragmented forests.

Abstract: -Successful invasion of eastern deciduous forests by the exotic shrub Lonicera maackii (Rupr.) Maxim. is well-documented, but little is known about seed germination or seedling establishment in this species. Our research suggested that most seeds are dispersed in a nondormant condition. After 88 days, mean cumulative germination percentages of untreated seeds ranged from 54-81% in light and from 31-55% in dark. Seedling density and light availability declined in parallel along transects extending from forest edges to forest interiors. Mean seedling densities ranged from 5-328 seedlings/mi2. Gap formation in forest interiors was not as conducive to seedling establishment as was the presence of edges. Still, this invasive shrub can establish seedlings throughout a wide range of light environments in

Restoring Caribbean Dry Forests: Evaluation of Tree Propagation Techniques

Abstract: Survival and height growth of tree seedlings and rooted cuttings introduced into artificially shaded and unshaded plots in a degraded dry forest were measured at intervals for nine months. Ten tree species were selected to represent a range of ecological characteristics of the dry–forest plant community on St. John, U.S. Virgin Islands. Of three propagule types – seeds, seedlings, and rooted cuttings – introduced to field plots, seedlings survived best (52%) over the initial nine-month period. Cuttings of six species rooted successfully in a shadehouse, but only two of these species survived the nine–month field experiment. Seed germination was low, under 11% for eight of ten species tested, and four species did not germinate. Subsequent mortality of seedling recruits was moderately high. Plumeria alba was the only species for which seedling height growth was not significantly greater than cutting height growth. Shading treatment (25% of full sun) significantly increased seedling survivorship (p= 0.03) but suppressed growth slightly for some species. Shading enhanced survival of seedlings produced from broadcast seeds, but not seed germination. Mortality occurred during dry periods, apparently from drought stress. Results suggest (1) that seedling introductions are the preferred propagule type (over seeding or rooted cuttings) for ecological restoration of degraded tropical dry forests, and (2) that some level of shading is required to increase the survivorship of many dry-forest species or to avert complete mortality of some species. This study suggests that early secondary dry forest may be best restored by underplanting within the existing vegetation. Sufficient shading suitable for growth of native dry-forest trees may be attained using a nurse crop of fast-growing leguminous trees.

Seed size, establishment sites and species coexistence in a Chilean rain forest

Abstract: . Seedling densities on the forest floor and on elevated microsites (logs and stumps) were compared for eight woody species in a temperate rain forest in southern Chile. Degree of association with elevated microsites varied significantly between species, showed no systematic relationship with reported shade tolerance, but was significantly negatively correlated with seed mass. Large-seeded Podocarpus nubigena established preferentially on undisturbed forest floor sites, whereas seedlings of small-seeded species such as Nothofagus nitida and Laurelia philippiana were found mainly on fallen logs and stumps. The abundance of large seedlings and saplings of N. nitida on logs/stumps, and the growth forms of canopy trees, confirm that recruitment of this species occurs mainly on decaying wood. The relationship between seed size and microsite preferences may be caused by effects of seed size on (1) ability to establish in forest floor litter and (2) retention of seeds on logs. Seedling occupancy of logs and stumps varied with state of decay. Few seedlings of any species were present on logs in the early stages of decay. N. nitida established earlier than the other species, attaining maximum abundance on wood in the middle decay classes. Species richness and overall seedling abundance were highest on wood in advanced stages of decay. Seed size differences are suggested as a determinant of differential utilization of forest floor heterogeneity, and hence of plant species coexistence.

Ficus stupenda germination and seedling establishment in a bornean rain forest canopy

Abstract: Factors limiting seed germination and seedling establishment of the hem- iepiphyte Ficus stupenda were investigated with two field experiments conducted in a Bornean rain forest canopy. In Experiment 1, seeds of F. stupenda were planted in potential establishment sites averaging 31 m above the ground in each of 45 dipterocarp trees. Twenty seeds each were planted in a total of 336 sites. Germination, survivorship, and growth were monitored over 1 yr, and examined in relation to microsite and host tree characteristics. The presence of substrate with good moisture retention (soil, rotting wood, or moss) was the most important factor for germination. Such substrates were most frequently associated with knothole sites in the canopy, which had the highest level of establishment success. Seedling survival to 12 mo was low (1.3% of planted seeds), especially considering that the best available sites in each tree were selected. Only 0.04% of seedlings showed vigorous growth after 12 mo. A seed-harvesting ant in the genus Pheidole significantly reduced germination success, and herbivory and desiccation killed many seedlings at later stages. In Experiment 2, seedling growth in natural canopy sites was compared with growth of seedlings in artificial planter boxes raised into the canopy in order to assess the relative quality of canopy sites. Planters were superior to natural sites for seedling survivorship and supported much more rapid seedling growth with a positive response to light level. Higher growth rates in planters compared with natural sites showed that water stress ap- peared to be the critical factor limiting seedling growth in the canopy, even in this very wet climate. Sites in the canopy with the optimal combination of conditions for fig seedling establishment appear to be very scarce. Ficus population densities may be limited by both biotic and abiotic factors reducing early recruitment success.