Showing papers on "Seedling published in 1986"

Seed size variation in Desmodium paniculatum. II: Effects on seedling growth and physiological performance

Abstract: (1) The effects of different environmental conditions on the growth and physiological performance of seedlings derived from different seed sizes were studied in the perennial herb Desmodium paniculatum. (2) The differences in seed weight are due to differences in the amounts of reserve substances. Seedlings from larger seeds produce longer roots than those from smaller seeds and are able to emerge from greater depths of soil. (3) Seed size is positively correlated with cotyledon area and weight, leaf area, root weight and overall seedling dry weight. Seedlings from different-sized seeds have similar relative growth rates and patterns of dry-matter allocation and do not show a differential response to shading. Seedlings from larger seeds respond to nutrient addition to a greater extent than those from smaller seeds. The contribution of epigeal cotyledons to the early growth of seedlings seems to depend more on their storage capacity than on their photosynthetic capacity. (4) Overall carbon gain and water-uptake capacity are proportional to seedling size. With reduced water availability, the advantage of seedlings from large and small seeds depends on whether they are grown singly or in competition. (4) Field experiments showed that seedlings from larger seeds were favoured over those from smaller seeds during the early stages of growth in a drier, more disturbed, site. Seed size had no effect on relative survival in a forest habitat. (6) Variation in seed size, within the range of that produced by a single plant, results in seedlings differing significantly in size and physiological characteristics. Seedlings from larger seeds may have an advantage over those from smaller seeds if both types are grown in competition.

Physiological controls over seedling growth in primary succession on an Alaskan floodplain

Abstract: Competitive interactions were more important than facilitative processes in controlling seedling growth in primary succession on the Tanana River floodplain in interior Alaska. Low soil and plant nitrogen levels in early succession were ameliorated by stands of alder associated with nitrogen-fixing bacteria. Facilitation was demonstrated in the greenhouse where alder (Alnus tenuifolia) soil enhanced growth of willow (Salix alaxensis) and poplar (Populus balsamifera) seedlings. Similarly, in the field, nutrient addition experiments and plant nutrient analyses demonstrated that all field- grown seedlings were least nutrient limited in alder stands. However, naturally occurring spruce (Picea glauca) seedlings and transplanted seedlings of alder and poplar grew least in alder stands where nitrogen levels were highest. Trenching and clear-cutting experiments demonstrated that alder stands inhibit seedling growth by root competition and shading. Physiological differences among the study species help explain their changing dominance through succession. Seedlings of species that establish in early succession (willow and poplar) grew more rapidly than alder. Late successional spruce seedlings had the slowest growth rates. In addition, spruce seedlings were more tolerant of the shaded conditions in alder stands than were the early successional species. Consequently, only spruce seedlings continued to establish in later stages. We conclude that this floodplain succession is a result of a complex interaction of life history, facilitative, competitive, and stochastic processes. To understand succession in such sites, the relative importance of these interactive processes must be investigated.

The effect of mycorrhizal infection on the response of betula papyrifera to nickel and copper

Abstract: Summary The role of ectomycorrhizas in the metal tolerance of birch seedlings from Sudbury, Ontario was investigated. Betula papyrifera Marsh, is one of the few tree species able to survive in the copper- and nickel-polluted area near Sudbury. Two types of birch seedlings were tested; those inoculated with Laccaria proxima (Boud.) Pat., Lactarius hibbardae Peck, Lactarius rufus (Scop, ex Fr.) Fries, or Scleroderma flavidum E. & E. isolates originating from the Sudbury area, and those which were not inoculated. Once the seedlings were infected, they were grown in sand culture containing 34 or 85 μM Ni, 32 or 63 Cu, or a control solution. At the low nickel concentration, the mycorrhizal plants, especially those infected with S. flavidum, grew significantly better than did non-mycorrhizal plants. At the higher nickel concentration, S. flavidum-infected seedlings weighed 86% of controls without nickel, while the other seedlings weighed only 52 to 61 % of control. The good growth of S. flavidum-infected birch seedlings may have been due to retention of nickel in the mycorrhizas. These seedlings had the highest root nickel contents and the lowest stem nickel contents. At the high concentration of copper, growth of the mycorrhizal seedlings was significantly reduced compared with the non-mycorrhizal seedlings. This reduction in growth of infected seedlings did not relate to an increase in the uptake or translocation of copper. Under the low copper treatment, infection with mycorrhizal fungi did not affect seedling growth. The potential role of iron and phosphorus in affecting host metal tolerance was investigated. Changes in the tissue concentrations of these elements did not relate to the effect of the fungi on metal tolerance.

Effect of seed size on seedling success in three species of sesbania (fabaceae)

Abstract: Variation in seed size may produce variation in seedling fitness, but the relationship is not simple. Differences in seed size within and among species may not have the same effects. We examined effects of differences in seed size within and among three species of Sesbania, S. macrocarpa, S. drummondii, and S. vesicaria, on seedling emergence and growth in the greenhouse and the field. Of the three species, the largest-seeded species, S. vesicaria, produced the largest, longest-lived seedlings in both the greenhouse and the field. Even though plant size differed, annual S. macrocarpa produced the same seed mass as annual S. vesicaria in the greenhouse. Within-species effects were less clear. In the greenhouse, S. vesicaria seedlings grown from large seeds remained largest until maturity, but the other species did not exhibit this effect. Some persistent within-species effects of seed size differences on height were observed in the field in 1981, but not in 1980, suggesting that field conditions increase the importance of seed size differences. Unscarified S. drummondii seeds germinated before seeds of the two annual species. Within species, larger seeds of the annuals and smaller seeds of the perennial germinated first. Differences among the species in the importance of seed size to seedling fitness may allow the species to have different patterns of regulation of reproduction in response to stress. Sesbania vesicaria showed the largest within-species effects of seed size and has the lowest plasticity in seed size, suggesting that patterns of plasticity have been selected such that the most important component of yield varies least. WHILE THEORETICAL CONSIDERATIONS predict that the production of larger seeds will yield larger, more competitive seedlings (Salisbury, 1942; Harper, Lovell, and Moore, 1970; Stebbins, 1971; Smith and Fretwell, 1974), studies of the relationship between seed size and seedling growth and survivorship have given mixed results (e.g., Twamley, 1967; Carelton and Cooper, 1972). Seed size may affect initial seedling growth, but not final seed yield (Black, 1959; but see Gross and Soule, 1981). Furthermore, the effects of seed size may be apparent only under competitive conditions (Black, 1958; Stanton, 1984) and earlier germination of small seeds may compensate for initial differences in seed size (Black and Wilkinson, 1963). Thus, although a number of studies of the effect of seed size on seedling success have been performed, our understanding of this relationship remains incomplete. ' Received for publication 30 July 1985; revision accepted 21 October 1985. David Braun weighed plant parts, Scott Shapiro sorted roots, and Kevin Ford and Mary Jean Hattrup assisted in the germination experiment. Tim Holtsford, Norm Ellstrand, Norma Fowler, and Don Levin provided helpful comments on an earlier draft of this manuscript. Financial support was provided by a research grant and a fellowship awarded to DLM from the graduate school of The University of Texas, Austin. Permission to work at Lake Somerville was provided by the U.S. Army Corps of Engineers, Ft. Worth District. 2 Present address: Department of Biology, Univ. of New Mex., Albuquerque, NM 87131. A number of factors may make the relationship between seed size and seedling fitness complex. First, the relationship between seed size and seedling quality may not be linear (Marshall, Fowler, and Levin, 1985a), so that all differences in seed size may not have uniform effects. For example, growth rates may differ among seedlings of varying size (Stebbins, 1976). Second, differences in seed size among species may represent physiological differences in addition to differences in size and, thus, have different effects than variation in size within species. Third, the nature of the size differences in seedlings-whether differences in leaf area, stem length or root length are involved-may determine the conditions under which increased seed size will have an impact on fitness. Fourth, the most important effect of seed size may be its influence on the kind of microsite in which germination and seedling establishment is possible (e.g., Gross and Werner, 1982; Gross, 1984) rather than its influence on seedling growth. Fifth, field conditions, which may involve microhabitat variation and competition, could either mask or exaggerate seed size effects seen in the greenhouse (Fenner, 1978; Gross, 1984). Finally, even if seed size and seedling size are correlated, plasticity in offspring size, rather than a constant size, may be adaptive in a variable habitat (Bradshaw, 1965; Capinera, 1979). Attempts to understand the importance of

Experimental studies of the evolutionary significance of sexual reproduction. iii. maternal and paternal effects during seedling establishment

Abstract: To determine whether genetic differences in fitness components exist among seeds and seedlings in a natural population, weighed propagules of six parents of Anthoxanthum odoratum from a reciprocal diallel cross were planted into the parental source population, a mown field. Seed families of maternal genotypes differed in germination success, while paternal families showed no detectable differences. Differential germination success could not be attributed to propagule weight. Seed families ranked differently in germination percentage in different blocks. No survivorship differences among parental seed families could be detected. There were significant cross × block × germination and cross × block × survivorship interactions; different crosses performed better or worse in different blocks. In some cases, crosses sired by different fathers within a maternal seed family differed in germination or survivorship, suggesting that natural selection may be capable of discriminating among juvenile genotypes within a maternal family despite the presence of large overall maternal effects. These results indicate that seedling establishment may differ according to genotype and that microsite heterogeneity may maintain genetic variation in juvenile traits in natural plant populations.

Allelopathic suppression of weed and nitrification by selected cultivars ofSorghum bicolor (L.) moench.

Abstract: Root exudates of 100 cultivars ofSorghum bicolor L. (Moench) were screened for their ability to inhibit seed germination and seedling growth ofAmaranthus retroflexus L. Exudates of some of the test cultivars were found to inhibit significantly seed germination and/or seedling growth ofA. retroflexus, and most of the inhibitory activity was found in neutral and acetone fractions of root exudates. Testing of aqueous extracts and decaying residues of four selectedSorghum cultivars (two toxic and two nontoxic through root exudation) revealed that all four cultivars significantly reducedA. retroflexus growth and nitrification processes with greater inhibition achieved by the toxic cultivars. This study suggests a potential biological control ofAmaranthus and nitrification by someS. bicolor cultivars.

A morphological index of Quercus seedling ontogeny for use in studies of physiology and growth.

Abstract: Summary Attempts to relate plant metabolic activity with developmental stage are often hindered by lack of an appropriate developmental index. Existing indices of morphological development are unsuitable for use with plants having a semideterminate, recurrently flushing pattern of growth as displayed by Quercus seedlings. We propose the following morphological index (QMI) to define the stages of Quercus seedling ontogeny: (1) radicle emergence; (2) epicotyl emergence from the soil; and (for each flush) (3) termination of elongation of the second internode, which corresponds with the period of most rapid stem elongation; (4) completion of elongation by all internodes, which corresponds with the period of most rapid leaf elongation; and (5) completion of elongation of the last leaf but one, which usually precedes closely the pause between one growth flush and another. The relationship between QMI and net photosynthesis by individual leaves of Quercus ruhra L. seedlings was determined. Net photosynthesis increased with QMI during a Hush, but at a particular QMI stage, generally decreased from one Hush to the next.

Moisture Loss as a Prerequisite for Seedling Growth in Soybean Seeds (Glycine max L. Merr.)

Abstract: Rosenberg, L. A. and Rinne, R. W. 1986. Moisture loss as a prerequisite for seedling growth in soybean seeds (Glycine max L. Merr.).—J. exp. Bot. 37: 1663-1674. As soybean seeds [Glycine max (L.) Merr.] develop, they undergo a change in seed moisture. When excised prematurely from the pod and planted, seeds do not exhibit seedling growth until 63 d after flowering (DAF) when the seed moisture has fallen below 60%. In contrast, seed germination (radicle protrusion) can occur when seeds as young as 35 DAF (68-79% moisture) are excised, but this germination does not lead to comparable seedling growth frequencies unless seeds are first given a moisture loss treatment to artificially reduce their moisture below 60%. A moisture loss treatment applied at 35 DAF thus enables seed to undergo the transition from germination (cell expansion) to seedling growth (cell division and expansion) to the extent that treated immature seed have a vigour index comparable to seeds matured on the plant (100%). The pattern of protein synthesis in vivo was examined in 35 DAF seed using [35S]-methionine incorporation. When moisture loss treatment was applied for 24 h to 35 DAF seeds, seeds synthesized several new polypeptides when compared with untreated seeds at the same developmental stage. The same seed samples showed 0% seedling growth in the absence of moisture loss treatment and 80% seedling growth when the treatment had been applied. Moisture loss from soybean seeds appears to be a prerequisite for the synthesis of new proteins which may be part of the metabolic process or processes that allow the soybean seed to undergo the transition from seed germination to seedling growth.

Ant-nest soil and seedling growth in a neotropical ant-dispersed herb.

Abstract: A major hypothesis concerning the benefits of myrmecochory, seed dispersal by ants, to plants is that ant nests are nutrient-enriched microsites that are beneficial to seedling growth. We experimentally test this hypothesis for a neotropical myrmecochore, Calathea ovandensis, asking two questions: 1) is soil of nests of a seed-dispersing ant chemically or structurally distinct from surrounding soils, and 2) do seedlings grow better in soil collected from ant nests than in randomly collected soil? We found that although ant-nest soil was significantly enriched in nitrate-nitrogen, magnesium, iron, manganese, cadmium and percent organic matter compared to randomly collected soil, seedling growth was not significantly improved by ant-nest soil.

Population dynamics of the shrub Acacia suaveolens (Sm.) Willd.: Seed production and predispersal seed predation

Abstract: Seed production and predispersal seed predation in the shrub Acacia suaveolens were examined over 3 consecutive years in eight populations in south-eastern Australia. Seed-crop sizes varied both between and within populations of different ages. Seed production was maximal in the first one to four flowering seasons after establishment, and then declined with plant age. The size of the annual seed-crop was also influenced by rainfall for that year. Predispersal seed predation varies between populations over fruiting seasons with the initial large seed-crops resulting in predator satiation. Within one fruiting season, no significant variation in the extent of predispersal seed predation was found in any of three populations studied. There were two major forms of predispersal seed loss: toss of whole fruits to Melanterius corosus (Coleoptera: Curculionidae) and external insect seed grazers, and loss of individual seeds within fruits to M. corosus. Exclusion experiments showed that seeds lost to these predispersal seed predators would otherwise have been matured by the parent plant. The effects of predispersal seed predation cannot be directly related to seedling recruitment. Indirectly, such predation may influence the dispersion of seeds in the soil profile and hence, subsequent recruitment.

The effects of simulated acid rain on germinative capacity, growth and morphology of forest tree seedlings

Abstract: Summary Acid rain-induced direct injury to forest tree seedlings was investigated in specially designed controlled-environment simulated-rainfall chambers. Seed germinative capacity, seedling survival, seedling growth and morphological responses to simulated rains of pH 5.6, 4.6, 3.6 and 2.6 were examined during the first growth cycle in 11 commercially important north temperate tree species. Germinative capacity was weakly responsive to rain pH, while seedling survival was more sensitive. No evidence of macroscopic foliar injury was observed at rain pH > 2.6. 1 reatment with pH 4.6 rain was sufficient to induce statistically significant growth reductions and morphological changes in coniferous seedlings. Response varied with species, treatment pH and parameter measured. No consistent growth stimulations were observed. Initiation of Primary needles, axillary meristems and shoot apex height were most affected by simulated pH. Deciduous species were considerably more resistant than coniferous species. Treatment with ram of pH 2.6 was generally required to induce significant growth reductions in deciduous seedlings.

THE RESPONSE OF SELECTED SALT-TOLERANT AND NORMAL LINES OF FOUR GRASS SPECIES TO NaCl IN SAND CULTURE

Abstract: Summary After 7 weeks' growth in varying NaCl concentrations in sand culture, dry matter production and tiller number were compared for the progenies of NaCl–tolerant selection lines and the Progenies of unselected control lines of Holcus lanatus L., Lolium perenne L., Dactylis glomerata L. and Festuca rubra L. The tolerant lines had been produced by selection at the seedling stage. In each species, selected lines produced significantly more dry matter and had greater tiller numbers than unselected material, particularly at high levels of NaCl. Shoot/root ratios differed significantly only in L. perenne, unselected material having a higher shoot/root ratio. These data confirm that for these four species, selection based upon differences in seedling root growth is a valid means of selecting for improved NaCl tolerance in adult plants, and that this tolerance does not lead to any reduced performance in the absence of NaCl.

Root growth potential, seedling morphology and bud dormancy correlate with survival of loblolly pine seedlings planted in December in Alabama.

Abstract: First-year survival of December-planted loblolly pine seedlings sampled from 20 nurseries ranged from 36 to 86%. Various characteristics of the seedlings including root growth potential (RGP), shoot/root ratio, root weight, and stem length were correlated with survival. A regression model using the number of new roots 2 0.5 cm and the shoot/root ratio accounted for 80% of the variation in firstyear survival. Alone, the number of new roots 2 0.5 cm accounted for 76% of the variation in survival. Foliar nutrients were not correlated with survival. Seedlings with a high proportion of quiescent buds at planting had a higher RGP and better survival than seedlings with dormant (endodormant) buds. The data suggest that seedlings with dormant buds should not be planted on sites where rapid new root growth is needed for survival.

Allelopathic influence ofSorghum bicolor on weeds during germination and early development of seedlings.

Abstract: The allelopathic interaction between sorghum [Sorghum bicolor (L.) Moench] and 10 species of grass and broadleaf weeds was investigated. Germination of weed seeds was slightly inhibited or stimulated, depending on species, when incubated in closed Petri dishes with germinating sorghum. Subsequent radicle and hypocotyl or coleoptile elongation of weeds was significantly inhibited by the germinating sorghum. For weeds interplanted with sorghum and grown under greenhouse conditions. The inhibitory effect on some weed species was still evident after 2 months of growth. Significant differences were found in the dry matter per weed plant grown in pots in proximity to sorghum vs. weeds grown in monoculture. Aqueous leachates from pots planted with sorghum alone or from a system in which sorghum roots protruded into water had strong allelopathic activity. These results indicate that water-soluble allelochemicals are produced by germinating sorghum seeds and that production of these substances continues during seedling growth.

Emergence and survival of bromus setifolius seedlings in different microsites of a patagonian arid steppe

Abstract: In a plant community of the arid steppe, structurally characterized by shrubs encircled by grasses and scattered tussocks with bare soil patches interspersed, the hypothesis of differential seedling survival in differentially protected microsites was tested. Seeds of Bromus setifolius were placed in the soil at two different depths and in two different microhabitats: leeward of a shrub and bare soil patch. No changes were recorded in the germination rate treatments. However, seadling survival under shrub protection was lower than in bare soil patches. Higher soil water potential in bare soil patches—probably due to smaller root biomass of established grasses—appeared to be the major determinant of the higher survival rate observed. A model based on seed density and seedling survival is proposed for seedling recruitment in relation to distance from the mother plant. The promotion of seedling establishment in the best suited microhabitats is visualized as a possible means of enhancing recovery of v...

The Control of Lateral Root Development in Cultured Pea Seedlings. I. The Role of Seedling Organs and Plant Growth Regulators

Abstract: Experiments were conducted to determine the influence of seedling organs on lateral root development in Pisum sativum `Alaska.' The cotyledons, root tip, and epicotyl were excised from seedlings containing roots of less than 3 cm. In some cases, plant growth regulators or nutritional factors were substituted for the excised organs. The number of emerged and initiated lateral roots was counted after 7 days. Cotyledon removal completely inhibited lateral root emergence and reduced the total number of initiated laterals by 40%. Cotyledon removal did not alter the number of laterals initiated per cm of primary root. Epicotyl removal reduced the number of emerged lateral roots but not the total number initiated. Root tip removal slightly increased the total number of lateral roots formed and emerged from the root region remaining after tip excision. Sucrose, nicotinic acid, pyridoxine, and thiamine did not promote lateral root emergence when provided as cotyledon substitutes. Growth regulator substitutions for...

Effect of seed manganese content on the growth of wheat (triticum aestivum) under manganese deficiency

Abstract: The importance of seed manganese (Mn) content for seedling growth of two wheat cultivars under soil Mn deficiency was demonstrated in growth cabinet experiments. Seed was obtained from different field sites (giving a Mn content range of 0.1 to 6.4 μg Mn seed−1), as well as from soaking seed in MnSO4 prior to sowing. Seed soaking greatly increased the seed Mn content, however, only about 15–20% of this additional Mn was recovered in the seedlings after 26 days growth. In these experiments, the seed rather than the soil provided the major source of plant Mn. Manganese critical deficiency levels (CDLs) were also obtained for leaves, shoots and roots. Increased grain yields from seed soaking were also evident in the field.

Isolation, culture and callus regeneration of protoplasts of wild and cultivated Helianthus species.

Abstract: Protoplasts were isolated from seedling roots, hypocotyls, and cotyledons of four cultivars of Helianthus annuus and from leaves of axenic shoot cultures of the wild species H. praecox, H. scaberimus and H. rigidus. Optimal culture conditions were established for the respective protoplast systems, using the agarose bead method of culture. Protoplast division was induced for all the species examined. In the case of the cultivars of H. annuus, hypocotyl and cotyledon protoplast division was sustained leading to callus formation, which in turn, could be induced to produce roots and organised meristematic regions in the presence of NAA and 6-BAP.

Seasonal patterns of net photosynthesis of loblolly pine from diverse origins

Abstract: Growth and photosynthesis were examined in seedlings of Pinustaeda L. (loblolly pine) from six widely separated provenances. The seasonal patterns of net photosynthesis were similar for each. Seedling net photosynthesis peaked in late October and net photosynthesis per unit leaf area peaked before midsummer and again in late October. When averaged over the entire season, seedling photosynthesis was greatest for Florida seedlings and least for Arkansas–Oklahoma and Texas seedlings. Seedling photosynthesis was strongly correlated with final size on all sampling dates and when averaged over the entire season. Both leaf area and net photosynthesis per unit leaf area contributed to the differences among provenances. Late season growth and photosynthesis, observed in the Florida provenance, increased provenance differences established early in the growing season.

Effects of laboratory germination, soil temperature and moisture content on the emergence of spring wheat

Abstract: In field investigations in a sandy-loam soil, probit percentage seedling emergence of commercial and aged seed lots of spring wheat (Triticum aestivum L., cv. Timmo) was a positive linear function of probit percentage laboratory germination and mean soil temperature and a negative linear function of percentage soil moisture content over the ranges 12·1–15·5% moisture content and 7·0–11·0 °C. In a laboratory investigation using the same soil a similar form of relationship was observed in six lots over a range of constant soil moisture contents between 10 and 18% and at constant soil temperatures of 8 and 20 °C. In all cases there was no interaction between any of these determinants of seedling emergence.Linear relationships between the mean rate of seedling emergence in the field (i.e. reciprocal of mean emergence time) and probit percentage laboratory germination and mean soil temperature were shown, but there was no obvious effect of mean scil moisture content between 12·1 and 15·5% on rate of field emergence. Seed lots of different percentage laboratory germination had the same base tsmperature for emergence (1·9 °C): differences between seed lots in mean emergence rate were due to different thermal time (day-degree) requirements for emergence; the thermal times required were a function of probit percentage germination in a standard laboratory test. The implications of these results in providing better advice on sowing rates are discussed.

Topographic Variation in the Abundance of Hieracium Floribundum: Relative Importance of Differential Seed Dispersal, Seedling Establishment, Plant Survival and Reproduction

Abstract: (1) The perennial herb Hieracium floribundum was found less often at the bottoms of small depressions (1-4 m diameter and 0-5-1 m deep) than at the tops in an abandoned pasture in Ontario, Canada. This study was to determine whether this variation was due to differential seed dispersal, seedling establishment, plant survival or reproduction. (2) More wind-dispersed seeds landed at the top of depressions (9300 m-2) than at the bottom (4100 m-2). (3) Topographic position had little effect on seedling establishment within a particular habitat type (i.e. vegetated or canopy removed or bare soil). However, the best habitat type for seedling establishment (bare soil) was more abundant at the top of depressions (6.7-26.4%) than at the bottom (0.4%). Consequently, seedling establishment would be more likely to occur at the top of depressions. (4) Seedlings planted at the top and bottom of depressions died at about the same rate during a 4-year period. The percentage of the transplants reproducing during this period was greater at the bottom of depressions. (5) Differential seed dispersal and seedling establishment were more likely responsible for the greater frequency of occurrence of H. floribundum at the tops of depressions than either differential survival or differential reproduction. This supports the view that critical factors determining plant distribution and abundance are those operating early in the life cycle.

Density-dependence in Salvia lyrata, a herbaceous perennial: the effects of experimental alteration of seed densities.

Abstract: (1) A demographic study of seedling populations of the perennial herb, Salvia lyrata L., was conducted from June 1979 to May 1983. The number of seedlings establishing varied widely from year to year. The half-life of the seedling population was about 10 months and seedling mortality rate declined with time. Correlation of seedling mortality with population density was low. (2) Field experiments showed that established S. lyrata individuals significantly reduced the proportion of seedlings emerging and surviving. Seed density had no demonstrable effect on the proportion of seedlings emerging over a range of densities (0-1440 seeds dm-2). There was thus no evidence of regulation by limitation of 'safe sites' in this species in nature. (3) Seedling mortality depended strongly on seed and seedling density. Fewer individuals survived in densities above 720 seeds dm-2 compared with densities of 240 and 480 seeds dm2. (4) Seedling growth was negatively density-dependent. Growth reduction, suffered at initially high densities, persisted after a large fraction of individuals had died. (5) Regulation of numbers of S. lyrata seedlings occurs primarily through the negative effects of adults. The densities of seedlings and year-old individuals are sufficient to reduce survival and growth only in infrequent clumps.

Establishment, suppression and growth of eucalyptus delegatensis R.T. Baker in multiaged forests. III: Intraspecific allelopathy, competition between adult and juvenile for moisture and nutrients, and frost damage to seedlings

Abstract: Field and pot experiments were designed to test the relative roles of allelopathy, competition for moisture and competition for nutrients in the suppression and growth of Eucalyptus delegatensis. In pot experiments litter cover was associated with slightly slower growth rates than in other treatments. A fertilization treatment was associated with increased growth rates in both trenched and untrenched situations in a field experiment, but the effect of fertilization was subdued in comparison with the effects of trenching or of total tree removal in the clear-felling treatment. Saplings and seedlings in the forest were under significantly greater moisture stress, as indicated by xylem pressure potential and stomata1 resistance, than those growing in the adjacent clear-felled areas. Surface soils in clear-felled areas had moisture contents above the level which caused seedling stress while surface soils within the forest were often below this level. These findings suggest that adult trees suppress seedling and sapling regrowth largely through their effect on soil moisture. However, another form of seedling growth suppression also occurs in the open as a result of frost damage.

Carbohydrate reserves in Pinus sylvestris seedling needles as an attribute of seedling vigor

Abstract: The carbohydrate reserve of bareroot Scots pine (Pinus sylvestris L.) seedlings was evaluated as means of describing seedling quality and capacity to withstand stress during nursery lifting, outplanting and acclimatization at the planting site. Carbohydrate concentrations in needles were followed through four spring storage treatments and the postplanting success and growth of seedlings monitored at two sites. The reduction in total glucose concentration in needles was affected by storage time and temperature. Depletion of carbohydrate reserves decreased needle growth, reduced the number of terminal buds, disturbed leader shoot formation, and consequently reduced shoot length. The depletion of reserves below a threshold concentration of ∼2 % total glucose during storage resulted in significant seedling mortality. A simple model for estimating the depletion of carbohydrate reserves based on dark respiration was evaluated as a measure of the accumulated strain during the storage. The application of carbohyd...

Reproductive ecology of jeffersonia diphylla (berberidaceae)

Abstract: The reproductive ecology of Jeffersonia diphylla (L.) Pers. (Berberidaceae) was investigated by studying its breeding system, ovule production, seed set, seed dispersal by ants and seed predation by rodents. This species flowers early in the spring and is facultatively autogamous. In a typical year fruit and seed set is high (90%), however, freezing temperatures from late spring frosts in 1983 and 1985 resulted in low fruit set (7% and 20%, respectively), and reduced seed set in those flowers that produced fruit. No differences in seed set between selfed and outcrossed flowers were observed over a two-yr period (1983-84). Ovule number per capsule increased with plant size as measured by leaf number. Seed set and seed wt were unaffected by leaf number unless leaves were removed after flowering was initiated. Jeffersonia diphylla is myrmecochorous. Ants removed seeds faster when seeds were placed in areas where J. diphylla plants were absent, suggesting that dispersal within J. diphylla populations is ant limited. Moreover, fresh (1 day old) seeds were removed by ants faster than 3 day old seeds. Seed predation by rodents prior to dehiscence from capsules is heavy in large populations (85-90%), and apparently negligible in small populations. Predation of seeds that are released from capsules is heavy (approx. 66%), particularly at night. Overall, seed predators consume about 96% of the seed crop in well established populations, but probably much less in small young populations. Hence, seedling recruitment is likely to be higher in small populations, whereas ramet production from rhizomes is the primary mode of propagation in large ones. The evolution of autogamy, early flowering, and myrmecochory are discussed in light of the results of this study.