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  • 1
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Plants of Cirsium vulgare (Savi) Ten. were cultivated under five different nitrogen regimes in order to investigate the effects of nitrogen supply on the storage processes in a biennial species during its first year of growth.External N supply increased total biomass production without changing the relationship between ‘productive plant compartments’ (i.e. shoot plus fine roots) and ‘storage plant compartments’ (i.e. structural root dry weight, which is defined as the difference between tap root biomass and the amount of stored carbohydrates and N compounds). The amount of carbohydrates and N compounds stored per unit of structural tap root dry weight was not affected by external N availability during the season, because high rates of N supply increased the concentration of N compounds whilst decreasing the carbohydrate concentration, and low rates of N supply had the opposite effect. Mobilization of N from senescing leaves was not related to the N status of the plants. The relationship between nitrogen compounds stored in the tap root and the maximum amount of nitrogen in leaves was an increasing function with increasing nitrogen supply. We conclude that the allocation between vegetative plant growth and the growth of storage structures over a wide range of N availability seems to follow predictions from optimum allocation theory, whereas N storage responds in a rather plastic way to N availability.
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  • 2
    ISSN: 1573-1561
    Keywords: Allelopathy ; Bunias orientalis ; root exudates ; leaf litter leachates ; soil cores ; growth inhibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Leaf extracts ofBunias orientalis were shown to inhibit seed germination of a variety of cultivar plant species and of species cooccurring withB. orientalis in the field. Root exudate solutions and leaf litter leachates ofB. orientalis were tested for their allelopathic activity using seedling growth assays. Additionally, in comparative seedling growth assays soil cores removed from denseB. orientalis stands were tested bimonthly for elevated allelopathic effects. The impact of root exudates on seedling growth was generally weak and varied between species. Similar results were obtained for the effect ofB. orientalis leaf litter leachates on seedlings grown in sand culture relative to the effect of leaf litter leachates of a plant species mixture. When soil as a growth substrate was used, no consistent differences in seedling growth were obtained between the two litter leachate treatments. In the soil core experiment seedlings grown in soil cores collected from a denseB. orientalis stand unexpectedly showed better performance than seedlings grown in soil cores collected from a nearby mixed plant stand withoutB. orientalis, at least in early spring and late autumn. Predominating nutrient effects are, therefore, assumed to conceal a potentially increased allelopathic effect of soil beneath denseB. orientalis stands. It is concluded that other factors than allelopathy must be investigated to explain the rapid establishment of dense stands of this alien plant species.
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  • 3
    ISSN: 1573-5052
    Keywords: Bunias orientalis ; Colonization ; Disturbance ; Invasion ; Regeneration ; Relative growth rate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The polycarpic perennial Bunias orientalis L. (Brassicaceae) introduced to Central Europe in the 18th century recently entered a phase of rapid spread accompanied by sudden establishments of extensive dominance stands mainly on roadside locations. We studied vegetation structure and expansion rate of B. orientalis stands and performed a series of experiments to investigate key factors that underlie the colonizing and establishment of B. orientalis. Reiterated observations exposed a high current expansion rate of B. orientalis populations and vegetation surveys of B. orientalis stands showed that these stands were mainly composed of Artemisietea and Arrhenateretea species. Regeneration experiments with root fragments revealed high regeneration capacities: root fragments of 3 cm length showed 93% regeneration, varying water content (10–50% water loss) and separation into root cortex and root stele yielded regeneration of 30 to 50%. In a field study high regrowth after mowing with varying mowing intensity indicates B. orientalis to be well adapted to disturbed sites as its preferential locations for development of dominance stands. Vegetative growth parameters were studied in two controlled growth experiments with elevated nutrient availabilities. B. orientalis exhibited a high sensitivity to nutrient addition and rosette sizes of maximal 90 cm were reached. Biomass was comparable or even higher than that of native ruderals grown in the same experiment. Measurements of reproductive parameters revealed a high reproductive effort (0.2 to 0.45 g g-1) even under intense mowing regimes, resulting in a dense seed bank with maximal values of about 400 fruits (≅550 seeds) l-1 soil. With respect to colonization and establishment of B. orientalis the results of our study enable the formulation of three hypotheses.
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  • 4
    ISSN: 1432-1939
    Keywords: Storage ; Accumulation ; Reserve formation ; Storage structure ; Biennial plants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Four biennial species (Arctium tomentosum, Cirsium vulgare, Dipsacus sylvester and Daucus carota) which originate from habitats of different nutrient availability were investigated in a 2-year experiment in a twofactorial structured block design varying light (natural daylight versus shading) and fertilizer addition. The experiment was designed to study storage as reserve formation (competing with growth) or as accumulation (see Chapin et al. 1990). We show that (i) the previous definitions of storage excluded an important process, namely the formation of storage tissue. Depending on species, storage tissue and the filling process can be either a process of reserve formation, or a process of accumulation. (ii) In species representing low-resource habitats, the formation of a storage structure competes with other growth processes. Growth of storage tissue and filling with storage products is an accumulation process only in the high-resource plant Arctium tomentosum. We interpret the structural growth of low-resource plants in terms of the evolutionary history of these species, which have closely related woody species in the Mediterranean area. (iii) The use of storage products for early leaf growth determines the biomass development in the second season and the competitive ability of this species during growth with perennial species. (iv) The high-resource plant Arctium has higher biomass development under all conditions, i.e. plants of low-resource habitats are not superior under low-resource conditions. The main difference between high- and low-resource plants is that low-resource plants initiate flowering at a lower total plant internal pool size of available resources.
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