Showing papers on "Seedling published in 1993"

The role of the monopteros gene in organising the basal body region of the Arabidopsis embryo

Abstract: The monopteros (mp) gene contributes to apical-basal pattern formation in the Arabidopsis embryo. mp mutant seedlings lack basal body structures such as hypocotyl, radicle and root meristem, and this pattern deletion has been traced back to alterations in the octant-stage embryo. Cells of the embryo proper and the uppermost cell of the suspensor fail to establish division patterns that would normally generate the basal body structures. The resulting absence of a morphological axis seems to be responsible for another phenotypic trait of mp seedlings, variable positioning of cotyledons. This relationship is suggested by weak mp seedling phenotypes in which the presence of a short hypocotyl is correlated with normal arrangement of cotyledons. Root formation has been induced in mp seedlings grown in tissue culture. This result supports the notion that the mp gene is required for organising the basal body region, rather than for making the root, in the developing embryo.

Seed Germination in Desert Plants

Abstract: During germination, the most resistant stage of the life cycle - the seed - changes to the most sensitive stage, namely the seedling. Therefore, in desert plant species, seed dispersal and subsequent germination in the optimum place are particularly critical parameters. Discussed here are the ways and means by which desert plants have adapted through the course of evolution to their extreme environment. Two such strategies which have evolved are outlined: plants with relatively large and protected seeds which germinate when the chance of seedling survival is high and the risk relatively low; and those with an opportunistic strategy - minute seeds which germinate after low rainfall. The reader is provided with an understanding of the complex influences acting upon each seed, traced from initial development to germination stage, regarding germination preparation and the subsequent survival.

Control of seedling emergence by ground cover and seed predation in relation to seed size for some old-field species

Abstract: A field experiment was conducted to test whether control of seedling emergence by ground cover and seed predation depended on seed size. Sown seeds of 12 oldfield species with seed masses ranging from 0.06 to 12.2 mg were used for the test. Species response to experimental removal of ground cover and (or) to the addition of a cage to reduce seed predation was recorded. Results were used to determine the relationship between seed mass and effects of ground cover and (or) seed predation on seedling emergence. Adding a cage to reduce seed predation did not increase seedling emergence significantly for each of the four species with the smallest seeds (<0.14 mg). In contrast, seedling emergence increased significantly for each of the eight species with larger seeds (...)

Post-fire litter microsites: Safe for seeds, unsafe for seedlings

Abstract: We explore the effect of post—fire microsites on seed and seedling distribution and hence their potential role in community restoration. A summer wildfire and control burn in a sclerophyll shrubland in mediterranean Australia produced mosaics of physically and chemically contrasting microsites of litter and sand. Most seeds (>75%) of all species released from the burnt canopies fell, or were redispersed by wind, into the litter patches after both fires. Data on microsite characteristics and wind exposure (fire intensity), height of fruits, time of release, and seed properties were required to interpret relative distribution between the litter and sand patches. Seeds remained equally viable (up to 100%) over summer—autumn in the litter and sand and had equally high rates and levels (up to 100%) of subsequent winter germination. However, seedlings were 2—3 times less likely to survive in the litter and survivors were 35% smaller than those in the sand by the end of the first summer. Banksia hookeriana was particularly vulnerable to microsite properties, whereas the needle—leaved Hakea polyathema showed only minor responses. Pre—summer thinning of seedlings in the litter increased survival of the remainder by 2 times and size of the survivors by 31%. The fire—sensitive, small—seeded B. hookeriana had 17 times more seeds in the backburn litter than the resprouting, larger—seeded B. attenuata, which more than compensated for its 3 times greater seedling mortality levels over the dry summer. Recruitment of species prone to density—dependent mortality in the litter was enhanced by the retention of some seeds in the sand where competition for water was minimal, as indicated by the 2.2 times greater stomal conductance of their seedlings in early summer.

Seedlings from Large Seeds Tolerated Defoliation Better: A Test Using Phylogeneticaly Independent Contrasts

Abstract: The characteristic seed size of a plant species may reflect evolution toward an optimal compromise between size and number of seeds produced. The extent to which large seed size conveys an advantage to a seedling probably varies according to circum- stances, and this may explain at least some ofthe great variation in seed size among species. Here we test whether large-seeded species are better able than small-seeded species to withstand defoliation at the seedling stage. We compared growth and survival of seedlings of 40 species of Australian angiosperms after removing 95% of their photosynthetic tissue shortly after emergence. We accounted for effects of phylogeny by selecting pairs of species that were "phylogenetically independent contrasts." That is, the phylogenetic path con- necting the two species of any pair was independent ofthe path connecting the two species of any other pair we used. We also selected the species so that the two members of each pair differed at least 10-fold in seed mass. Therefore, each pair provided an independent case for examining the consequences of evolutionary divergence in seed size. We found that the larger seeded species survived loss of photosynthetic tissue better than the smaller seeded species in 14 ofthe 16 pairs for which there was a significant difference in survival. The extent to which growth of survivors was reduced by loss of photosynthetic tissue also differed in 8 pairs, with the large-seeded species being less affected in 6 of these cases. We conclude that large seed size is generally associated with greater ability of seedlings to cope with loss of photosynthetic tissue. Consequently, large seed size may be favored in any circumstances in which seedlings are likely to experience carbon deficit early in develop? ment.

Seedling recruitment and the maintenance of clonal diversity in plant populations-a computer simulation of Ranunculus repens

Abstract: 1 A computer simulation model is developed to examine the effects of varying levels of seedling recruitment, mortality and rates of clonal growth on genet diversity in populations of the clonal perennial herb, Ranunculus repens. 2 It is shown, following an initial colonization event, that there is a rapid loss of genets from populations in which there is no further seedling recruitment, and that such populations become dominated by a few large clones. Nevertheless coexistence of a high density of genets is possible in the short term in the nonequilibrium situation occurring immediately after a large scale disturbance. 3 The input of only a few seedlings each year into a population of ramets accelerates the loss of founder genets but acts as a powerful mechanism for maintaining genet diversity in populations. Varying the level of density-dependent mortality and the rate of clonal growth also influences genet diversity. 4 Taking the results of all the simulations together it is demonstrated that it is the ratio of seedling to ramet recruits that is crucial in determining the genetic architecture of clonal plant populations both in terms of the number and size hierarchy of genets. Significant variation in the relationship between population structure and the ratio of seedling to ramet recruits was related primarily to low initial population densities and subsequent low seedling inputs. 5 The low ratio of seedling to ramet recruits observed in many plant populations where seedling recruitment occurs within established populations is shown to be sufficient to maintain quite high genet densities relative to the total number of ramets, unless there is strong competition between genets. 6 Inequality in the genet size of clonal plants increases with time and also with a decrease in the ratio of seedling to ramet recruits, except at very low values where there is again a decrease in inequality. The development of genet size hierarchies in clonal plants is compared with that of aclonal plants.

Successional Status, Seed Size, and Responses of Tree Seedlings to CO^2, Light, and Nutrients

Abstract: We studied how an enriched CO2 atmosphere, in a fully crossed design of light and nutrients, influenced 1 st-yr seedling growth in six New England deciduous forest tree species. The species, in the order of increasing shade tolerance, were gray birch (Betula populifolia), ash (Fraxinus americana L.), red maple (Acer rubrum L.), red oak (Quercus rubra L.), yellow birch (Betula alleghaniensis Britton), and striped maple (Acer pensylvan- icum). Elevated CO2 environments significantly stimulated the seedling growth of all six species. Generally this was more pronounced in low light. The greatest stimulation was found under the condition of low light and high nutrients. However, individual species responded differently to elevated CO2 levels. Among the three early-successional species, gray birch, ash, and red maple, a significant increase in seedling growth under elevated CO2 conditions was found only with high nutrients. The three late-successional species grown under elevated CO2 conditions (red oak, yellow birch, and striped maple) showed a greater percentage increase in seedling growth in low light than in high light. Thus, for the early-successional species, the degree of enhancement of seedling growth by elevated CO2 levels was more sensitive to nutrient levels, while in the late-successional species the enhancement was more sensitive to the level of light. Moreover, species with large seeds (e.g., red oak) exhibited a greater response to elevated CO2 levels under low light than species with small seeds (e.g., gray birch). The results emphasize the importance of plant species as well as other environmental resources in modifying the response of plants to elevated CO,. Considering the light and nutrient environment observed in forest gaps of various sizes, the results of the present experiment suggest seedling regeneration in New England deciduous forests may be altered in a future high CO2 environment.

Influences of neighbouring plants on seedling establishment in limestone grassland

Abstract: . Influences of neighbouring plants on seedling establishment of six dicotyledonous species was investigated in a nutrient-poor limestone grassland (Mesobrometum) in northern Switzerland. Microsites with different vegetational structure were created and seeds sown in them. The fate of emerging seedlings was followed for one or two years. A plant surviving its first growing season was regarded as established. Shelter by neighbouring plants appeared to be necessary for the establishment of Arabis hirsuta and Primula veris. Because of drought and frost heave, hardly any seedlings of these species established in gaps (4 - 21 %). In microsites with vegetation, their survival was significantly higher (40–57 %). Neighbouring plants slightly reduced the survival of Plantago lanceolata and Sanguisorba minor, but these species established well both in gaps (74 - 81 %) and in vegetated microsites (54 - 67 %). Medicago lupulina established well in all microsites in one year (71 - 79 %), but poorly in the next year (18–32 %). Linum catharticum emerged poorly in one year and was completely extinguished by a fungal pathogen the following year. The overall conclusion is, that gaps are of minor importance for recruitment of these species in this grassland. Physical hazards and pathogens control seedling establishment to a greater extent than competition by neighbouring plants. Some species are hardly able to establish without shelter of vegetation. Seed size is an important factor for success of establishment, especially in gaps. It is suggested, that the relatively low productivity and the absence of litter accumulation (due to mowing and biomass removal) are important conditions for the observed behaviour of the seedlings and juvenile plants in this community.

Effects of Meadow Vole Population Density on Tree Seedling Survival in Oil Fields

Abstract: Voles (Mammalia: Arvicolidae) are reported to be key consumers of tree seedlings in some habitats, but their importance in old—field succession is not known. Natural populations of voles fluctuate widely in density, and we sought to determine the effects of vole density on seedling predation. We used a randomized block design, with meadow voles maintained at three density levels (low, medium, high; three replicates of each) in field enclosures of 17 mo. We introduced young seedlings of five tree species into the enclosures. Three cohorts of seedlings were planted under intact vegetation, and one was planted in small areas from which we had cleared all vegetation. Overall predation rates were high for all cohorts planted under intact vegetation. There was a significant effect of vole density on seedling predation rate for two of these three cohorts; nearly all seedlings were destroyed in enclosures with high vole density. Predation rates by voles were highest for white ash and red maple, intermediate for white pine, and lowest for eastern hemlock and red oak. For the cohort planted in small clearings, mean predation rates were low and there was no density effect. Spatial variation in seedling predation rates was higher in enclosures with low and medium densities of voles than in high—density enclosures. In three of the cohorts there was a significant block effect, with the same block consistently having the highest predation rates. Evidence suggests that the block effect was caused by genetic differences among voles. Seedling predation by voles can: (1) delay old—field succession by reducing the number of tree invaders; (2) create patchiness by concentrating surviving seedling in certain microsites; and (3) alter relative abundances of invading species via differences in palatability or apparency. We suggest that the population dynamics of voles be viewed as a keystone process in old—field succession.

Seed and seedling ecology of neotropical melastomataceae

Abstract: Models of gap-phase regeneration in tropical wet forests are based primarily on studies of canopy trees. These paradigms are derived from studies of a small number of species whose life history traits place them easily into "pioneer" or "climax" species. Woody plants of the forest understory, subcanopy trees and shrubs, are known to affect significantly regeneration dynamics in treefall gaps, yet we lack fundamental information on life history characteristics of understory plants that could permit their incorporation into gap regeneration models. We investigated intra- and interspecific variability in early life history characteristics of understory Melastomataceae species of different growth forms and adult distributions from the lowland tropical rain forest at La Selva Biological Station, Costa Rica. We examined germination patterns in vitro (22 species), effects on germination of passage through birds (5 species), seedling establishment in the field (3 species), and growth in different light environments (8 species). Established seedlings were significantly more abundant in gaps than in nearby under- story sites. This pattern was generally applicable to all melastomes studied, regardless of the habitat where adults were normally most abundant. Seedlings were more common in the root pits and on the root mounds of uprooted trees, even though there was less light available to the seedlings in these microsites than elsewhere in the gaps. In a series of germination trials in vitro, most seeds germinated readily within 1-2 wk. Comparisons of germination rates between seeds collected from bird droppings and seeds extracted from fruits by hand gave varied results. With one exception, seeds of shade-tolerant species germinated more slowly following passage through birds, while seeds from high-light- demanding species germinated more rapidly after passing through birds. Seeds of three common species were sown directly into different microsites within gaps and understory control sites. In contrast to the germination trials, emergence percentages in the field ranged from 4% in understory sites to 21 % in gap centers. Survival after 1 yr was low (0.1%- /0.4%). After 1 yr, these seedlings were small (<2 cm tall) and produced few leaves. In similar light environments in the shade-house, melastome seedling survival was between 80% and 100%, and growth increased with increasing light levels from 2% (corresponding to understory sites) to 20% (small gap centers) of full sun. With the exception of two species common to abandoned pastures and river banks, the species used in the shade-house growth experiments did not show significant increases in growth with increases in light from 20% to 40%. Suites of early life history traits described for tropical tree species are not consistent with the variation in pattern seen within this one family of understory species.

Seed banks as a neglected area of biogeographic research: a review of literature and sampling techniques

Abstract: The article highlights a comparatively neglected area of biogeographical research - seed banks and the distribution of seeds in the soil. The article reviews some of the relevant literature on seed banks and the methods for their study. Attention is focused on aspects of seed banks of particular relevance to biogeographers, with detailed examples drawn from seed bank studies in both temperate and tropical environments. In the review of the seed bank literature, the topics covered include the seed banks of successional communities and the size of seed banks in different vegetation types. The species composition of seed banks in different plant communities is discussed, particularly the degree of correlation between the species composition of seed banks and associated ground flora. The relationships between seed persistence, depth of burial in the soil and soil properties, such as moisture and pH, are explored. Seed bank heterogeneity is examined and a number of studies which have attempted to describe and measure the spatial variability of seed banks are summarized. Ways of classifying seed banks in terms of seed bank strategies are explained. The role of seed banks in conservation is discussed, for example in restoration projects, where preferred species have been lost from the vegetation but survive in the seed bank. The relevance of seed banks for the conservation of rare species and in landscape management is considered. Lastly, the contribution of seed banks to the recovery of vegetation following disturbance in various plant communities is discussed. In the review of seed bank sampling techniques, the subjects considered include methods of sample collection, the sampling intensity required for reliable estimates of seed density, a consideration of the relative merits of random and systematic sample distribution, as well as the importance of the timing of sampling. Various methods for the estimation of seed numbers in samples are appraised; these either involve extraction of seeds from the soil, followed by seed identification or enumeration by germination and seedling identification. Problems of analysing seed bank data are considered and several useful techniques for data analysis are suggested. Finally, the article draws attention to areas of future seed bank research for biogeographers and plant ecologists.

Effects of salicylic acid on plant-water relationships.

Abstract: Soybean seedlings [Glycine max (L.) Merr.] were used as the test species to study the allelopathic influence of salicylic acid (SA) on short- and long-term plant water status. Plants were grown in greenhouse conditions in nutrient culture medium amended with SA. Treatments were initiated 10 days after germination and continued for either 14 or 28 days. The threshold for inhibition of seedling growth over a 28-day treatment was 0.15 mM SA. Seedlings grown with 0.3 mM SA consistently had higher leaf diffusive resistance and lower transpiration and water potentials than control plants. The stable carbon isotope ratio (13C:12C) in tissue from both the 0.15 and 0.30 mM SA-treated plants was significantly higher than control seedlings, indicating SA caused a chronic water stress during the 28-day treatment. These data show that an interference with plant-water relationships is one mechanism whereby this allelochemical inhibits plant growth.

A life-history based study of population genetic structure: seed bank to adults in plantago lanceolata.

Abstract: We explored the extent to which the soil seed bank differed genetically and spatially in comparison to two actively growing stages in a natural population of Plantago lanceolata. All seed-bank seeds, seedlings, and adults of P. lanceolata within eight subunits in a larger population were mapped, subjected to starch gel electrophoresis, and allozyme analysis in 1988. Gel electrophoresis was also used to estimate the mating system in two years, 1986 and 1988. The spatial distributions of seeds, seedlings, and adults were highly coincident. Allele frequencies of the dormant seeds differed significantly from those of the adults for four of the five polymorphic loci. In addition, a comparison of the genotype frequencies of the three life-history stages indicated that the seed bank had an excess of homozygotes. Homozygosity, relative to Hardy-Weinberg expectations, decreased during the life cycle (for seed bank, seedlings, and adults respectively: Fit = 0.19, 0.09, 0.01; Fis = 0.14, 0.04, -0.12). Spatial genetic differentiation increased sixfold during the life cycle: (for seed bank, seedling and adults: Fs1 ∗∗∗ = 0.02, 0.05, 0.12). The apparent selfing rate was 0.01 in 1986 and 0.09 in 1988. These selfing rates are not large enough to account for the elevated homozygosity of the seed bank. Inbreeding depression, overdominance for fitness, and a "temporal Wahlund's effect" are discussed as possible mechanisms that could generate high homozygosity in the seed bank, relative to later life-history stages. In Plantago lanceolata, the influence of the mating system and the "genetic memory" of the seed bank are obscured by the time plants reach the reproductive stage.

Volatile monoterpenes as potential parent structures for new herbicides

Abstract: Eighteen volatile monoterpenes, which are among the major constituents of essential oils from plants, were screened for phytotoxicity to several crop and weed species. Several monoterpenes containing an oxygen function severely inhibited germination of four different annual weeds while concurrently displaying little effect on soybean germination. Soybeans varied in their sensitivity to various monoterpenes (measured by seedling growth), with a-terpineol and geraniol selectivity inhibiting weed seed germination while having little or no effect on soybeans. All of the monoterpenes tested exhibited relatively high germination and growth inhibition to corn and wheat. Nomenclature: Cinmethylin, exo-l-methyl­ 4-(I-methylethyl)-2-((2-methylphenyl)methoxy).7-oxabicy. clo (2.2.1) heptane; Italian ryegrass, Lolium multiflorum Lam. #3 LOLMU; large crabgrass, Digitaria sanguinalis (L.) Scop. #DIGSA; redroot pigweed, Amaranthus retroflexus L. #AMARE; velvetleaf, Abutilon theophrasti Medik. #ABUTH; alfalfa, Medicago sativa (L.) 'Vernal'; corn, Zea mays (L.) 'Pioneer 3377'; cucumber, Cucumis sativus (L.) 'Edmonson'; soybeans, Glycine rna;\: (L.) Merr. 'Williams 82'; wheat, Triticum aestivum (L.) 'Coker 68-19'.

The regeneration niche of the grey mangrove (Avicennia marina): effects of salinity, light and sediment factors on establishment, growth and survival in the field

Abstract: Field observations of seedlings and saplings of Avicennia marina showed patterns that correlated with salinity, light and sediment. Models that account for these observations were subsequently tested in a series of field experiments. Establishment varied within an estuary under controlled conditions but was not related to salinity or sediment type. Seedling survival was uniform over 3 years regardless of position in estuary and sediment type. Seedling densities and survival under canopies or in canopy gaps were not significantly different. However, seedling growth and density of saplings were greater in canopy gaps. Experiments involving manipulations of canopies showed no differences in seedling survival under canopies or in light gaps, but addition of slow-release fertilizer enhanced growth and survival in canopy gaps and under canopies. Long-term comparison of areas denuded of a canopy and with sediment disturbance showed enhanced establishment and survival when compared with areas with canopy gaps but with undisturbed sediments. Overall there appears to be no restriction to establishment of propagules within mangrove stands other than the supply of propagules and tidal or wave action. In contrast, recruitment to the sapling stage appears to be restricted by light and sediment resources. We suggest that propagules need to establish in a regeneration niche for seedling recruitment to the sapling stage. This differs from the view that seedlings in the under-storey are analogous to a seed pool in the soil.

Seed development in relation to desiccation tolerance: A comparison between desiccation-sensitive (recalcitrant) seeds of Avicennia marina and desiccation-tolerant types

Abstract: Development of the highly desiccation-sensitive (recalcitrant) seeds of primarily one species, Avicennia marina, is reviewed and compared with the ontogeny of desiccation-tolerant (orthodox) seeds. A. marina seeds undergo no maturation drying and remain metabolically active throughout development, which grades almost imperceptibly into germination. While PGR control of histodifferentiation is essentially similar to that characterizing desiccation-tolerant seeds, the phase of growth and reserve deposition is characterized by exceedingly high cytokinin levels which, it is proposed, promote a sink for assimilate import. While some starch accumulation does occur, the predominant reserves are soluble sugars which are readily available for the immediate onset of seedling establishment upon shedding. ABA levels are negligible in the embryo tissues during seed maturation, but increase in the pericarp, which imposes a constraint upon germination until these outer coverings are sloughed or otherwise removed. The pattern of proteins synthesized remains qualitatively similar throughout seed development in A. marina, and no LEA proteins are produced. This suggests both that seedling establishment is independent of maturation proteins and that the absence of LEAs and desiccation sensitivity might be causally related. The study on A. marina reveals that for this recalcitrant seed-type, germination per se cannot be defined: rather, it is considered as the continuation of development temporarily constrained by the pericarp ABA levels. This leads to a reexamination of the role of rehydration as key event sensu stricto, in the germination processes in desiccation-tolerant (orthodox) seeds.

Interactions oftrans-cinnamic acid, its related phenolic allelochemicals, and abscisic acid in seedling growth and seed germination of lettuce.

Abstract: Phenolic compounds have been identified as the most common allelochemicals produced by higher plants. Inhibitions of cinnamic acid, its related phenolic derivatives, and abscisic acid (ABA) on seedling growth and seed germination of lettuce were studied.trans-Cinnamic acid, ando-,m-, andp-coumaric acids inhibited the growth of etiolated seedlings of lettuce at concentrations higher than 10−4 M and seed germination above 10−3 M. Coumarin inhibited seedling growth and seed germination at 10−5 M or above. Chlorogenic acid inhibited seedling growth above 10−4 M, but did not inhibit seed germination at 10−5−5×10−3 M. Low concentrations (below 10−3 M) of caffeic and ferulic acids promoted the elongation of hypocotyls, but higher concentrations (over 10−3 M) inhibited seedling growth and seed germination. These phenolic compounds and abscisic acid had additive inhibitory effects both on seedling growth and seed germination. The inhibition on lettuce was reversed by caffeic and ferulic acids at concentrations lower than 10−3 M except for the inhibition of germination by coumarin. These results suggest that in naturetrans-cinnamic acid,o-, m-, p-coumaric acids, coumarin, and chlorogenic acid inhibit plant growth regardless of their concentration. However, caffeic and ferulic acids can either promote or inhibit plant growth according to their concentration.

Seedling establishment in adult neighbourhoods-intraspecific constraints in the regeneration of the bunchgrass Bouteloua gracilis.

Abstract: In order to determine the effect of conspecific adult neighbours and opening size on the process of seedling establishment in Bouteloua gracilis, seeds were added to naturally occurring openings of bare soil, and water was provided up to and beyond the time of adventitious root development of seedlings. Exclusion of roots of neighbours was accomplished using steel tubes sunk in the soil of openings. Adult neighbours affected emergence, survival and performance of seedlings in the whole observed range of opening sizes (10, 20 and 30 cm in diameter). With neighbours present (no root exclusion), seedlings produced few tillers regardless of opening size, and had higher survival only in the 30-cm-diameter openings (...)

Onion (Allium cepa L.) Seedling Emergence Patterns can be Explained by the Influence of Soil Temperature and Water Potential on Seed Germination

Abstract: A theory is outlined that seedling emergence patterns in the field are largely generated by the influence of soil water potential on a critical event (i.e. the initiation of radicle growth) that determines the base water potential for germination. Above this base the mean rate and distribution of seedling emergence are largely determined by temperature. This proposal was expressed as a parsimonious stochastic model to test whether patterns of seedling emergence recorded in field experiments could be explained. The model applies current understanding of the influence of water potential and thermal time on germination under controlled conditions to the variable environment of horticultural seed beds. Where possible, parameter values were taken from the literature, others were inferred from laboratory experiments on seed germination and seedling emergence. The model accurately predicts the onset of seedling emergence and the occurrence and timing of subsequent seedling flushes in a wide range of seed bed conditions. The study indicates that a co-ordinated use of existing seed-bed preparation techniques to retain soil moisture for initial seed imbibition and limited irrigation, timed to coincide with the critical period when radicle growth is initiated in the seed population, may provide an approach to improving crop uniformity that is simple and practical.

A Comparative Study of Plasticity in Seedling Rooting Depth in Drying Soil

Abstract: Maximum depth of vertical root penetration into the soil (i.e. rooting depth) and shoot growth were measured for seedlings of 42 species of vascular plants in both unwatered and watered soil columns. The ratio of rooting depth in unwatered soil to watered soil was calculated to quantify plasticity in rooting depth. The objectives were to determine whether all species show equal plasticity in rooting depth and to measure the extent to which plasticity in seedling rooting depth influences the ability of seedlings to sustain growth in drying soil. Seedlings were allowed to initiate growth in continuously moist sand during a 21-day pretreatment. Two watering treatments (unwatered vs. watered daily) were then applied for an additional 21 days (...)

Seed rain and advanced regeneration in a tropical rain forest

Abstract: By comparing seed rain, seedling and sapling community structures we assessed the possible role played by vertebrate seed dispersal as a structuring factor in advanced regeneration of closed-canopied sites in the tropical rain forest of Los Tuxtlas, Mexico. Seed weight, initial morphology of seedlings and species abundance were also analyzed to determine if these traits influenced the probability of establishment in the shade.

Application of Weed Seedbank Ecology to Low-Input Crop Management

Abstract: Pesticide use in the United States is concentrated in the Corn Belt, mainly in the form of herbicides on corn (Zea mays) and soybean (Glycine max). If this chemical load to the environment is to be reduced, without appreciably affecting crop yields, an intimate understanding of weed ecology is necessary. For annual weeds in the U.S. Corn Belt, critical ecological information includes seedbank density, seed dormancy, seedling emergence, and environmental variables that regulate these factors. For three weeds (Setaria spp., Amaranthus retroflexus, and Chenopodium album) in Minnesota, this information is summarized, and its application to weed management is illustrated. If weed seedbank densities (0-10 cm depth) are 1000 seeds/M2 typically result in such high seedling populations that nonchemical control mea- sures alone cannot prevent large crop yield losses. About one-half of all arable fields harbor seedbanks with densities > 1000 seeds/M2. The proportion of buried seeds giving rise to seedlings is controlled by seed dormancy, which in turn is governed partially by April temperatures (in Minnesota), whereas the timing of subsequent seedling emergence is determined by soil temperature and soil water. EMERG models simulate daily percentages of emerging weed seedlings for April through June, when most Corn Belt crops are sown. If seedbeds of fields with potential seedling densities of 100 seedlings/M2 are prepared and sown when simulated emergence exceeds -80% for C. album, 85% for A. retroflexus, and 99% for Setaria spp., then mechanical weed control sufficiently reduces weed populations and crop yield losses are negligible. Accordingly, mechanical weed control may be substituted economically for chemical con- trol, but only when accompanied by adequate understanding of the ecology of pertinent weed species.

Factors related to seedling growth in a boreal Scots pine stand: a spatial analysis of a vegetation-soil system

Abstract: The spatial structure of vegetation and soil properties of a patchy Scots pine (Pinussylvestris L.) forest of 1 ha was described and examined in relation to the height growth of pine seedlings in t...

Allelopathy in agroforestry systems: the effects of leaf extracts of Cupressus lusitanica and three Eucalyptus spp. on four Ethiopian crops

Abstract: The potential allelopathic effect ofCupressus lusitanica, Eucalyptus globulus, E. camaldulensis andE. saligna on seed germination, radicle and seedling growth was investigated with four crops:Cicer arietinum (chickpea),Zea mays (maize),Pisum sativum (pea) andEragrostis tef (teff). Aqueous leaf extracts of all the tree species significantly reduced both germination and radicle growth of the majority of the crops mostly starting from concentrations of 1% or 2.5%. The shoot and root dry weight increase of the crops was significantly reduced after 10 weeks treatment with leaf extracts. Among the four crops, chickpea and teff were most susceptible with respect to germination, and teff with respect to growth. From the overall data the leaf extracts of the four tree species can be arranged according to increasing allelopathic potential:C. lusitanica, E. globulus, E. saligna andE. camaldulensis. It is suggested that the planting ofE. camaldulensis andE. saligna in integrated land use systems should be minimized, whereas the use ofC. lusitanica andE. globulus seems less environmentally damaging in this respect.

Effects of nitrogen supply and elevated carbon dioxide on construction cost in leaves of Pinus taeda (L.) seedlings

Abstract: Seedlings of loblolly pine (Pinus taeda L) were grown under varying conditions of soil nitrogen and atmospheric carbon dioxide availability to investigate the interactive effects of these resources on the energetic requirements for leaf growth Increasing the ambient CO2 partial pressure from 35 to 65 Pa increased seedling growth only when soil nitrogen was high Biomass increased by 55% and photosynthesis increased by 13% after 100 days of CO2 enrichment Leaves from seedlings grown in high soil nitrogen were 70% more expensive on a g glucose g−1 dry mass basis to produce than those grown in low nitrogen, while elevated CO2 decreased leaf cost by 35% Nitrogen and CO2 availability had an interactive effect on leaf construction cost expressed on an area basis, reflecting source-sink interactions When both resources were abundant, leaf construction cost on an area basis was relatively high (818±30 g glucose m−2) compared to leaves from high nitrogen, low CO2 seedlings (563±30 g glucose m−2) and low nitrogen, low CO2 seedlings (671±27 g glucose m−2) Leaf construction cost appears to respond to alterations in the utilization of photoassimilates mediated by resource availability

Aspects of variation in a neotropical seed dispersal system

Abstract: This paper explores the causes and consequences of seed and seedling mortality of the tree Virola nobilis (Myristicaceae) Central Panama in order to understand the advantage to local seed dispersal by birds and monkeys. Post-dispersal mortality due to insects (primarily Conotrachelus spp., Curculionidae) accounts for 30–35% of seed and seedling death during the first 12 weeks after seed fall. Because more seeds and seedlings are killed under and near fruiting trees than 15–45 m away, seed dispersal confers a 20–40 fold advantage on seeds carried 45 m from fruiting adults. In contrast, >60% of seed and seedling death during the first year is due to seed predation by mammals, with >90% due to mammals among the <2% seeds that survive until maternal endosperm is exhausted ±12 weeks after seed fall. Mortaliy due to mammals is independent of distance from parent trees, confering no advantage to seed dispersal. Insects account for variation in mortality attributable to distance effects, mammals to between site effects.

Seedling emergence model for velvetleaf

Abstract: Consistent postemergence weed control requires information on the timing of weed emergence. Information is especially important for velvetleaf (Abutilon theophrasti Medikus), which interferes with many crops over a broad geographic range. The objective of this study was to develop a model that predicts the timing and proportional extent of velvetleaf seedling emergence. Environmental effects on seed germination and seedling emergence, used to construct the model, were determined in growth chambers or from published sources. Two variables drive the model: average daily soil temperature of the seed zone (5-cm soil depth) and daily rainfall. The model requires initialization by four seed zone parameters: (i) soil water content at the start of the simulation period, (ii) soil water holding capacity, (iii) soil bulk density, and (iv) a water retention curve relating percent soil water to soil water potential. The model was validated using field data collected in Illinois in 1967 and 1969 and in Minnesota in 1990. Regressions of predicted and observed seedling emergence resulted in r² values of 0.91, 0.97, and 0.98 for 1967, 1969, and 1990, respectively. Correspondence (regression coefficients) between predicted and observed seedling emergence was 0.83, 1.01, and 1.01 for 1967, 1969, and 1990, respectively. Both sets of statistics indicate the model predicts velvetleaf seedling emergence reliably. Joint contribution from USDA-ARS and Dep. of Agronomy and Plant Genetics, Univ. of Minnesota. Minnesota Agric. Exp. Stn. Sci. J. Ser. no. 18,644.

Survival of Acer pseudoplatanus L. (sycamore) seedlings on metalliferous soils

Abstract: SUMMARY Seeds and seedlings of Acer pseudoplatanus L. (sycamore) were collected at sites contaminated by metals, originating either from mining spoil or from aerial deposition from metal processing industry, and at a number of relatively uncontaminated sites. Seedling growth was examined in relation to site of origin, both in nutrient solutions with elevated metal concentrations and in reciprocal transplant experiments in soils from the sites. Metal tolerance was not detected and there was no significant difference between plants from the different sites of origin. It was found, however, that roots could proliferate in uncontaminated zones of the soil and that, even in contaminated soils, most seedlings used in growth tests survived for at least three years despite impaired growth. Seedlings growing at the contaminated sites showed phytotoxic symptoms associated with high metal levels, but apparently healthy seedlings and saplings of different ages were also found. Some form of low level innate tolerance may be involved but it is suggested that phenotypic plasticity is more important than previously thought, potentially allowing survival until favourable conditions are encountered either temporally or spatially.

Effect of Inoculation with Azospirillum brasilense Strains on the Germination and Seedlings Growth of the Giant Columnar Cardon Cactus (Pachycereus pringlei)

Abstract: Wild Cardon cactus seeds were inoculated with Azospirillum brasilense strains Cd and Sp-245 to improve seed germination and seedling growth parameters. Differential germination responses were related to the bacterial strain. A. brasilense Cd (the type strain for the species A. brasilense) significantly decreased seed germination. A. brasilense Sp245 (a known beneficial bacteria for cereal plants) significantly increased the germination of the seedlings at the same inoculum concentration. Both bacterial strains improved several plant growth parameters related to seedling survivability (height, diameter, volume and the volume/surface ratio) and decreased the aging process of the seedling spines. Both strains of A. brasilense survived in the cactus rhizosphere for about 300 days after seed inoculation. This study adds further evidence that A. brasilense should be considered as a non-specific beneficial bacteria and we propose the inoculation of Cardon cactus seeds as a possible means of enhancing seedling growth in nurseries.