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Young Seedlings (young + seedling)
Selected AbstractsAllocation of above-ground growth is related to light in temperate deciduous saplingsFUNCTIONAL ECOLOGY, Issue 4 2003D. A. King Summary 1Allocational shifts in response to light may be an important factor in allowing plants to survive in shade, while increasing their extension rates and competitive ability in sun. To investigate this response, the allocation of above-ground growth between leaves, branches and stems was studied in saplings of Acer pensylvanicum L. and Castenea dentata (Marsh.) Borkh. in the Appalachian mountains of western Virginia, USA. Measurements of current leaf biomass, current and past year leaf numbers and the growth ring widths of branches and stem were used to estimate biomass partitioning for saplings growing in locations ranging from forest understorey to large openings. 2Both species showed higher leaf area per unit leaf biomass (SLA) and higher allocation of above-ground growth to leaves in shade than in sun. 3There were no differences between species in the slopes of the relationships of allocation and SLA vs estimated irradiance, but SLA was significantly greater in A. pensylvanicum than in C. dentata at a given light level. Hence, somewhat lower production per unit leaf area is required to maintain the canopy in A. pensylvanicum, consistent with foresters' ratings of greater shade tolerance for this species. 4Greater foliar allocation in shade than sun has also been observed in broad-leaved evergreen saplings, but generally not in seedlings. This difference is probably related to differences in size and age between seedlings and saplings. Young seedlings typically show exponential growth with no immediate foliar losses, while shaded saplings lie closer to the steady state where new leaves replace old ones with little additional stem growth. 5Thus trees shift their allocation patterns in an acclimatory fashion, depending on their size and light environment, with the costs of replacing senesced leaves becoming of consequence as juveniles age. [source] Responses of gas exchange and growth in Merkus pine seedlings to expected climatic changes in ThailandGLOBAL CHANGE BIOLOGY, Issue 6 2001Jarkko Koskela Abstract Responses of gas exchange and growth in Merkus pine (Pinus merkusii Jungh. et de Vriese) seedlings to changing climate were analysed for high- and low-altitude sites in Thailand. A gas exchange model, based on the optimality approach, derived the effect of drought from the probability of rains. A carbon-and nitrogen-balance growth model applied structural regularities of a tree and a modification of functional balance between foliage and fine roots as growth- guiding rules. Adaptation to local climates was incorporated in the models. The simulations yielded physiologically reasonable behaviour for annual photosynthesis (A) and transpiration (E) in relation to the distributions of precipitation over the course of a year. An annual temperature increase of 2 °C and a prolonged dry season (scenario 2) reduced A by 5,11% and E by 5,8% as compared to present climate (scenario 1). Doubled CO2 concentration and the increased temperature (scenario 3) enhanced A by 56,59% and E by 14%. Simultaneously these changes (scenario 4) increased A by 41,53% and E by 1,5%. Simulated growth in scenario 1 fitted reasonably well to field data. By the age of five years, simulated total biomass (TB) and height (h) were reduced by 31,67% and 12,42%, respectively, in scenario 2 compared to scenario 1. In scenario 3, TB and h increased by 279,330% and 94,191%, and in scenario 4, by 83,241% and 55,69%, respectively. Large increases in TB and h are explained by the exponential growth phase of the young seedlings. These results suggest that climatic changes enhance growth and thus shorten the duration of the grass stage in these seedlings. However, the effects of climatic changes on growth depend strongly on how rainfall seasonality is altered in SE Asia because prolonged drought episodes may retard the fertilizing effects of the increasing CO2 concentration. [source] Phenotypic Plasticity of Life History Characteristics: Quantitative Analysis of Delayed Reproduction of Green Foxtail (Setaria viridis) in the Songnen Plain of ChinaJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 6 2008Hai-Yan Li Abstract Green foxtail (Setaria viridis L.) is a common weed species in temperate regions. Research on the effect of delayed reproduction on the phenotypic plasticity and regularity of the vegetative and reproductive growth is of vital significance for understanding population regulation and control of the weed in the growing season. Green foxtail seeds were sown every 10 days from 25 June to 24 August of 2004. The growth and production metrics were measured via harvesting tufts and statistical analysis was carried out. The results showed that the reproductive tillers, seed number, seed biomass and one thousand-seed weight of plants at the first sowing (25 June) approximately increased 28.8, 7 827.0, 1 104.0 and 12.3 times compared with that at the last sowing (24 August), respectively. Total tillers, reproductive tillers and height increased linearly as the reproductive period delayed, however, biomass increased exponentially. Quadratic equations best explained the relationships between the delayed reproductive period and seed number, inflorescence length, one thousand-seed weight, seed biomass. Based on the quantity and quality of seed production, weeding young seedlings emerging before July can be the most effective weed-control strategy in the Songnen Plain. [source] Defence Responses of Calli and Seeds of Hevea brasiliensis to Zoospores and the Elicitin of Phytophthora palmivoraJOURNAL OF PHYTOPATHOLOGY, Issue 11-12 2008Nion Chirapongsatonkul Abstract The defence responses of calli and seeds of two cultivars (resistant; BPM-24 and susceptible; RRIM600) of the rubber tree, Hevea brasiliensis, against zoospores and elicitin purified from its pathogen, Phytophthora palmivora, were investigated. Both zoospores and elicitin induced the biosynthesis of the phytoalexin, scopoletin (Scp), in Hevea calli ranging from 5 × 105 to 4.5 × 106 zoospores/ml and 0.5 to 2 ,g elicitin/g fresh weight of calli. At the highest concentration of zoospores (4.5 × 106 zoospores/ml) or elicitin (2 ,g/g fresh weight of calli), the rate of Scp production was fastest but then it rapidly decreased and produced lower peak value than detected at the optimum concentration. The decline of Scp level at the highest zoospore/elicitin concentration was correlated to the amount of cell death measured by Evans Blue method. Peroxidase (POD) activities in Hevea calli were also measured using the optimum level of zoospores or elicitin. Induction of Scp preceded the production of Scp POD and o -dianisidine POD then followed by the guaiacol POD. The Scp and POD accumulations were approximately two to three times higher in the resistance cultivar than those in the susceptible one. As the responses of the calli to elicitin were faster than those to the zoospores, it demonstrates that zoospores require more time to act on the host cells. The pattern of Scp and POD activities monitored in elicitin-treated Hevea seeds was similar to that of Hevea calli after treating with zoospores or elicitin. Therefore, the callus cultures could be used as a tool for studying other defence mechanisms in H. brasiliensis. The achieved knowledge will be applied to enhance resistance and led to the protection of Hevea young seedlings from the pathogen in the plantation. [source] Plant ontogeny and chemical defence: older seedlings are better defendedOIKOS, Issue 5 2009Arnaud Elger Although patterns of seedling selection by herbivores are strongly influenced by plant age and the expression of anti-herbivore defence, it is unclear how these characteristics interact to influence seedling susceptibility to herbivory. We tracked ontogenetic changes in a range of secondary metabolites (total phenolics, alkaloids and cyanogenic glycosides) commonly associated with seedling defence for nine sympatric British grassland species. Although there was marked variation in concentrations of secondary metabolites between different species, we found a consistent increase in the deployment of phenolics, alkaloids and cyanogenics with seedling age for six of the seven dicotyledonous species examined. The two grass species by contrast exhibited low levels of secondary metabolites across all developmental stages, possibly due to an investment in structural (silica phytoliths) defence. Our results corroborate species-specific patterns of seedling herbivory observed in field studies, and offer some explanation for the relatively high sensitivity to herbivore attack frequently observed for relatively young seedlings compared with their older conspecifics. Our results also support predictions made by the growth,differentiation balance hypothesis regarding ontogenetic changes in resource allocation to anti-herbivore defence for a range of potential chemical defences and across a range of sympatric plant species presumably subject to broadly similar selective pressures at the regeneration stage. [source] A comparison of ammonium, nitrate and proton net fluxes along seedling roots of Douglas-fir and lodgepole pine grown and measured with different inorganic nitrogen sourcesPLANT CELL & ENVIRONMENT, Issue 3 2008B. J. HAWKINS ABSTRACT Significant spatial variability in NH4+, NO3, and H+ net fluxes was measured in roots of young seedlings of Douglas-fir (Pseudotsuga menziesii) and lodgepole pine (Pinus contorta) with ion-selective microelectrodes. Seedlings were grown with NH4+, NO3,, NH4NO3 or no nitrogen (N), and were measured in solutions containing one or both N ions, or no N in a full factorial design. Net NO3, and NH4+ uptake and H+ efflux were greater in Douglas-fir than lodgepole pine and in roots not exposed to N in pretreatment. In general, the rates of net NH4+ uptake were the same in the presence or absence of NO3,, and vice versa. The highest NO3, influx occurred 0,30 mm from the root apex in Douglas-fir and 0,10 mm from the apex in lodgepole pine. Net NH4+ flux was zero or negative (efflux) at Douglas-fir root tips, and the highest NH4+ influx occurred 5,20 mm from the root tip. Lodgepole pine had some NH4+ influx at the root tips, and the maximum net uptake 5 mm from the root tip. Net H+ efflux was greatest in the first 10 mm of roots of both species. This study demonstrates that nutrient uptake by conifer roots can vary significantly across different regions of the root, and indicates that ion flux profiles along the roots may be influenced by rates of root growth and maturation. [source] Genetic modification of the fatty acid unsaturation of phosphatidylglycerol in chloroplasts alters the sensitivity of tobacco plants to cold stressPLANT CELL & ENVIRONMENT, Issue 1 2004A. SAKAMOTO ABSTRACT The cis -unsaturated molecular species of phosphatidylglycerol (PG) in chloroplasts have been implicated in the chilling sensitivity of plants. Homozygous lines of transgenic tobacco (Nicotiana tabacum) that overexpressed the cDNA for glycerol-3-phosphate acyltransferase, a key enzyme in the determination of the extent of cis -unsaturation of PG, were established from a chilling-sensitive squash (Cucurbita moschata). In transgenic plants, the proportion of saturated plus trans -monounsaturated molecular species of PG increased from 24 to 65%. However, this change did not affect the architecture of the chloroplasts. Chilling stress decreased the growth and biomass production of young seedlings of transgenic plants more severely than those of wild-type plants, and this observation suggests that the changes in the proportion of cis -unsaturated PG affected not only leaves but also developing plants. Chilling stress also damaged inflorescences. In particular, the abscission of flower buds and inflorescence meristems from transgenic plants occurred more frequently than that from wild-type plants. Thus, it is likely that decreases in the proportion of cis -unsaturated PG enhanced the sensitivity to chilling of reproductive organs. [source] Memories of winter: vernalization and the competence to flowerPLANT CELL & ENVIRONMENT, Issue 11 2000S. D. Michaels ABSTRACT The promotion of flowering in response to a prolonged exposure to cold temperatures (i.e. winter) is a useful adaptation for plant species that flower in the spring. This promotion is known as vernalization and results in a permanent memory of cold exposure. While the physiology of vernalization has been extensively studied in many species, the molecular mechanism of vernalization remains largely unknown. Recent studies, however, have revealed some of the molecular events that create the requirement for vernalization. In Arabidopsis, naturally occurring late-flowering ecotypes and plants containing late-flowering mutations in the autonomous floral-promotion pathway are relatively late flowering unless cold treated. The vernalization requirement of these late-flowering ecotypes and autonomous-pathway mutants is largely created by an upregulation of the floral inhibitor FLOWERING LOCUS C (FLC). After cold treatment, as imbibed seeds or young seedlings, FLC transcript levels are downregulated and remain low for the remainder of the plant's life, but return to high levels in the next generation. Plants containing a constitutively expressed 35S:FLC construct remain late flowering after cold treatment, indicating that FLC levels must be downregulated for vernalization to be effective. Thus the epigenetic downregulation of FLC appears to be a major target of the vernalization pathway and provides a molecular marker of the vernalized state. [source] Phytophthora pinifolia sp. nov. associated with a serious needle disease of Pinus radiata in ChilePLANT PATHOLOGY, Issue 4 2008A. Durán During the course of the past three years, a new disease of Pinus radiata, referred to as ,Daño Foliar del Pino' (DFP) has appeared in the Arauco province of Chile and subsequently spread to other areas. The disease is typified by needle infections, exudation of resin at the bases of the needle brachyblasts and, in younger trees, necrotic lesions in the cambium, which eventually girdle the branches. The disease causes the death of young seedlings and mature trees can also succumb after a few years of successive infection, probably hastened by opportunistic fungi such as Diplodia pinea. Isolations on selective medium for Phytophthora spp. led to the consistent isolation of a Phytophthora sp. from needle tissue. DNA sequence comparisons for the ITS rDNA and cox II gene regions, and morphological observation showed that this oomycete represents a previously undescribed species for which the name Phytophthora pinifolia sp. nov. is provided. This new species is characterized by unbranched sporangiophores, and non-papillate, sub-globose to ovoid sporangia that are occasionally free from the sporangiophore with medium length pedicels. Despite using a number of oospore inducing techniques, oogonia/antheridia were not observed in isolates of P. pinifolia. Pathogenicity trials with P. pinifolia showed that it is pathogenic to P. radiata and causes rapid death of the succulent apical parts of young plants. Phytophthora pinifolia is the first Phytophthora known to be associated with needles and shoots of a Pinus sp. and its aerial habit is well matched with the occurrence and symptoms of DFP in Chile. [source] The Arabidopsis SPA1 gene is required for circadian clock function and photoperiodic floweringTHE PLANT JOURNAL, Issue 5 2006Masaki Ishikawa Summary Arabidopsis phytochrome A (phyA) regulates not only seed germination and seedling de-etiolation but also circadian rhythms and flowering time in adult plants. The SUPPRESSOR OF PHYA-105 (SPA1) acts as a negative regulator of phyA-mediated de-etiolation of young seedlings, but its roles in adult plants have not yet been described. Here, we show that SPA1 is involved in regulating circadian rhythms and flowering time in plants. Under constant light, the abundance of SPA1 protein exhibited circadian regulation, whereas under constant darkness, SPA1 protein levels remained unchanged. These results indicate that the SPA1 protein is controlled by the circadian clock and light signals. In addition, the spa1-3 mutation slightly shortened the circadian period of CCA1, TOC1/PRR1 and SPA1 transcript accumulation under constant light. Phenotypic analysis showed that the spa1-3 mutant flowers early under short-day (SD) but not long-day (LD) conditions. Consistent with this finding, transcripts encoding flowering locus T (FT), which promotes flowering, increased in spa1-3 under only SD conditions, although the CONSTANS (CO) transcript level was not affected under either SD nor LD conditions. Our results indicate that SPA1 not only negatively controls phyA-mediated signaling in seedlings, but also regulates circadian rhythms and flowering time in plants. [source] Early ontogenetic trajectories vary among defence chemicals in seedlings of a fast-growing eucalyptAUSTRAL ECOLOGY, Issue 2 2010CLARE MCARTHUR Abstract Ontogenetic changes in leaf chemistry can affect plant,herbivore interactions profoundly. Various theoretical models predict different ontogenetic trajectories of defence chemicals. Empirical tests do not consistently support one model. In Eucalyptus nitens, a fast-growing tree, we assessed early developmental changes to seedlings, in foliage concentrations of nitrogen and the full suite of known secondary (defence) chemicals. This included the terpene, ,-pinene, whose impact on marsupial herbivory is unknown. To test for the influence of abiotic conditions on the ontogenetic trajectories we overlaid a nutrient treatment. Ontogenetic trajectories varied among compounds. Sideroxylonals and cineole were barely detected in very young seedlings, but increased substantially over the first 200 days. Total phenolic concentration increased fourfold over this time. In contrast, ,-pinene concentration peaked within the first 60 days and again between 150 and 200 days. Nutrients altered the degree but not the direction of change of most chemicals. A shorter trial run at a different season showed qualitatively similar patterns, although ,-pinene concentration started very high. We investigated the effect of detected levels of ,-pinene and cineole on food intake by two mammalian herbivores, common brushtail possums (Trichosurus vulpecula) and red-bellied pademelons (Thylogale billardierii). Under no-choice conditions neither terpene reduced intake; but with a choice, possums preferred ,-pinene to cineole. The ontogenetic trajectories of most compounds were therefore consistent with models that predict an increase as plants develop. Published data from later developmental stages in E. nitens also confirm this pattern. ,-Pinene, however, was the only secondary compound found at significant levels in very young seedlings; but it did not constrain feeding by marsupial herbivores. Models must allow for different roles of defensive secondary chemicals, presumably associated with different selective pressures as plants age, which result in different ontogenetic trajectories. [source] The effect of soil compaction on germination and early growth of Eucalyptus albens and an exotic annual grassAUSTRAL ECOLOGY, Issue 6 2009ALISON K. SKINNER Abstract Most agricultural land has been compacted to some degree by heavy machinery or livestock trampling. This legacy is expected to influence the success of tree seedling recruits in farmland areas where natural regeneration is being encouraged. We investigated the impact of soil compaction on seedlings of a woodland eucalypt (Eucalyptus albens) and an annual grass competitor (Vulpia myuros) in a laboratory experiment. Replicate soil cores were created at five bulk density levels; 1.0, 1.1, 1.2, 1.3 or 1.4 Mg m,3 with a soil water content of 20%. The depth of root penetration declined linearly with increasing bulk density, resulting in a decrease in root depth of around 75% in the most compacted soil compared with the least compacted soil for both species. Shoot length and primary root length did not vary between soil bulk density levels for either species, but seedlings responded to increasing levels of compaction with oblique (non-vertical) root growth. Results suggest that young seedlings of both E. albens and V. myuros will be more susceptible to surface drying in compacted than uncompacted soils and therefore face a greater risk of desiccation during the critical months following germination. Any competitive advantage that V. myuros may have over E. albens is not evident in differential response to soil compaction. [source] Root/Shoot Allocation and Root Architecture in Seedlings: Variation among Forest Sites, Microhabitats, and Ecological Groups1BIOTROPICA, Issue 3 2003Horacio Paz ABSTRACT I analyzed patterns of variation in root mass allocation and root morphology among seedlings of woody species in relation to environmental factors in four Neotropical forests. Among forests, I explored the response of root traits to sites varying in water or nutrient availability. Within each forest, I explored the plastic response of species to different microhabitats: gaps and understory. Additionally, I explored evidence for life history correlation of root and shoot traits by comparing species differing in their successional group (light-demanding [22 spp.] or shade tolerant [27 spp.]) and germination type (species with photosynthetic cotyledons or species with reserve cotyledons). At each forest site, young seedlings from 10 to 20 species were excavated. A total of 55 species was collected in understory conditions and 31 of them were also collected in gaps. From each seedling, six morphological ratios were determined. Allocation to roots was higher in forest sites with the lowest soil resources. Roots were finer and longer in the most infertile site, while roots were deeper in the site with the longest dry season. Seedling traits did not differ between germination types. Shade tolerant species allocated more to roots and developed thicker roots than light-demanding species. Light-demanding species showed stronger plastic responses to habitat than shade tolerant species, and species with photo-synthetic cotyledons showed lower plasticity than species with reserve cotyledons. Overall, these results suggest that among Neotropical species, root allocation and root morphology of seedlings reflect plant adjustments to water or nutrient availability at geographic and microhabitat scales. In addition, life history specialization to light environments is suggested by differences among groups of species in their allocation to roots and in their root morphology. RESUMEN Analicé los patrones de variación en la asignación de biomasa y en la morfología de raíces de plántulas de especies leñosas en relación a factores ambientales en cuatro bosques Neotropicales. Entre los bosques, exploré la respuesta promedia de características de las plántulas en sitios que varían en disponibilidad de agua o nutrientes en el suelo. Dentro de cada bosque, exploré la respuesta fenotípica de las especies entre claros y sotobosque. Además, explore correlaciones de la historia de vida de las especies con características de raíces y parte aérea, comparando especies con diferente hábito sucesional (demandante de luz [22 spp.] o tolerante a la sombra [27 spp.]) y tipo de germinación (especies con cotiledones fotosintéticos o cotiledones de reserva). En cada bosque, se excavaron plántulas de 10 a 20 especies manteniendo la integridad de sus raíces. Se colectaron 55 especies en el sotobosque y 31 de ellas fueron colectadas también en claros. De cada plántula obtuve seis parámetros morfológicos de raíces y parte aérea. La asignación de biomasa a raíces fue mayor en los bosques con menos recursos. Las plántulas desarrollaron raíces más finas, y con mayor longitud por unidad de superficie fotosintética, en el sitio menos fértil. En cambio, las raíces tendieron a ser más profundas en relación al área fotosintética en el sitio más estacional. Las especies tolerantes a la sombra asignaron más biomasa a raíces y desarrollaron raíces más gruesas que las especies demandantes de luz. Las características morfológicas de las plántulas no difirieron entre tipos de germinación. Las especies demandantes de luz mostraron mayor plasticidad al hábitat en la asignación de biomasa a raíces, que las especies tolerantes a la sombra. Las especies con cotiledones fotosintéticos mostraron menor plasticidad al hábitat en la asignación de biomasa a raíces que las especies con cotiledones de reserva. En conjunto, mis resultados sugieren que para especies Neotropicales la asignación de biomasa y la morfología de raíces en plántulas reflejan ajustes de las plantas a la disponibilidad de agua o nutrientes a escala geográfica y de micro-hábitat. Además, se sugiere que la asignación de biomasa y la morfología de raíces son componentes del síndrome de especialización a ambientes lumínicos en el bosque. [source] | ||||||||||||||||||||||