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  • 1
    ISSN: 1573-1480
    Keywords: wetlands ; forested catchments ; dissolved organic carbon ; carbon cycling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Most Precambrian Shield forested catchments have some wetland component. Even small riparian wetlands are important modifiers of stream chemistry. Dissolved organic matter (DOM) is one of the most important products exported by wetlands in streams. Stratigraphic control of hydraulic conductivity generally leads to decreasing conductivity with depth. Thus important flowpaths occur in the uppermost organic rich layers and are reflected in chemical profiles of dissolved organic carbon (DOC). Accumulation of DOC in peat porewaters is the net effect of production, consumption and transport. DOC profiles vary with degree of interaction with the surrounding upland catchment and distance from the edge of the wetland as well as internal processes within the wetland. In wetlands, DOM production is offset by flushing resulting in decreasing DOC concentrations with increasing flows. Despite old carbon (2,000 to 3,000 years) at relatively shallow depths, 14C activity in DOC exported from wetlands is mostly modern (recent carbon), consistent with shallow flowpaths and export of DOM from shallow organic rich horizons. In contrast, the source area for DOM in upland catchments with developed B horizon soils increases with antecedent soil moisture conditions resulting in increasing DOC concentrations with higher stream flows. Activity of 14C in stream DOC from upland catchments span a range from low activities (older carbon) similar to B horizon soil water during dry moisture conditions to values slightly less than modern (more recent carbon) during high moisture conditions. The more modern carbon activities reflect the increased contribution of the organic rich litter and A horizon soil layers in the area immediately bordering the stream under wet antecedent moisture conditions. Reduced hydrologic export or loss of wetlands under drier climatic conditions may result in in larger fluctuations in stream DOC concentrations and reduced DOM loads to lakes.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-515X
    Keywords: climate change ; dissolved organic carbon (DOC) ; forested catchments ; nutrient export ; Precambrian Shield streams ; storm runoff
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Dissolved organic carbon (DOC) concentrations and DOC export arestudied during storms to examine the relationship between DOCconcentration and stream discharge and to assess the importance of stormson DOC export. Storms were monitored in seven subcatchments within twosmall watersheds (Harp 4--21 and Harp 3A) on the Precambrian Shield inCentral Ontario, Canada. Stream DOC concentrations increase during stormsby as much as 100% and 410% in Harp3A and Harp 4--21 respectively. The seasonal regression between DOC andstream discharge is significant in subcatchments without wetlands(r2 〉 0.7) but is not significant in thetwo subcatchments with small wetland areas (r2 〈0.06). On average, regressions based on weekly data yield accurate estimatesof DOC export but the variation in regressions among individual storms andthe small number of high DOC samples result in uncertainties of more than30% in DOC export. The period-weighted calculation ofDOC export from weekly data underestimates export by 14%and 22% in Harp 3A and Harp 4--21 respectively. Stormswere responsible for 57% to 68% of theDOC export in the autumn and 29% to 40%of the DOC export in the spring. A single large storm accounted for31% of the autumn DOC export in Harp 3A. The importanceof individual storms for DOC export and the variation in the relationshipbetween DOC and stream discharge among storms make it difficult to predictthe effects of climate change on DOC export and DOC concentrations.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-515X
    Keywords: dissolved organic carbon ; forested catchments ; lakes ; 14C ; 13C ; carbon isotopes ; carbon cycling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Export of dissolved organic carbon (DOC) from forested catchmentsis governed by competing processes of production, decomposition, sorptionand flushing. To examine the sources of DOC, carbon isotopes (14Cand 13C) were analyzed in DOC from surface waters, groundwatersand soils in a small forested catchment on the Canadian Shield in centralOntario. A significant fraction (greater than 50%) of DOCin major inflows to the lake is composed of carbon incorporated into organicmatter, solubilized and flushed into the stream within the last 40 years. Incontrast, 14C in groundwater DOC was old indicating extensiverecycling of forest floor derived organic carbon in the soil column beforeelution to groundwater in the lower B and C soil horizons. A small uplandbasin had a wide range in 14C from old groundwater values atbaseflow under dry basin conditions to relatively modern values during highflow or wetter antecedent conditions. Wetlands export mainly recently fixedcarbon with little seasonal range. DOC in streams entering the small lakemay be composed of two pools; an older recalcitrant pool delivered bygroundwater and a young labile pool derived from recent organic matter.The relative proportion of these two pools changes seasonally due thechanges in the water flowpaths and organic carbon dynamics. Althoughchanges in local climate (temperature and/or precipitation) may alterthe relative proportions of the old and young pools, the older pool islikely to be more refractory to sedimentation and decomposition in thelake setting. Delivery of older pool DOC from the catchment andsusceptibility of this older pool to photochemical decomposition mayconsequently be important in governing the minimum DOC concentrationlimit in lakes.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-515X
    Keywords: carbon cycling ; dissolved organic carbon (DOC) ; forested catchments ; nutrient export ; Precambrian Shield streams ; storm runoff
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Dissolved organic carbon (DOC) concentrations and export were studied in two small catchments in central Ontario to examine DOC sources and to assess the hypothesis that organic matter adjacent to the stream is a significant contributor of DOC during storms. Different DOC dynamics and exports were observed according to the depth of the riparian water table. In Harp 4-21, riparian flowpaths were predominantly through A and upper B soil horizons and riparian soils contributed between 73 and 84% of the stream DOC export during an autumn storm. In Harp 3A, riparian flowpaths were predominantly through lower B horizons. Consequently, riparian soils were less important and hillslopes contributed more than 50% of the stream DOC export in subcatchments without wetlands during storms. Wetlands and adjacent soils contributed significantly to DOC export in Harp 3A; 8% of the total catchment area exported 32 to 46% of the storm runoff DOC. DOC export dynamics in wetlands and riparian soils were distinctly different. In wetlands, transport was affected by leaching and flushing of DOC at the wetland surface leading to lower DOC concentrations with successive storms. In riparian soils, groundwater flowpaths were more important and stronger positive relationships between discharge and DOC concentration were observed. Precipitation, throughfall and stemflow were minor sources of stream DOC during storms and contributed less than 20% of the total export.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Plant cell, tissue and organ culture 49 (1997), S. 29-33 
    ISSN: 1573-5044
    Keywords: explant state ; genotype ; growth regulators ; organogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A study has been carried out on several Amaranthus L species and breeding lines (A. caudatus, A. cruentus, A. hybridus, A. hypochondriacus), some of which have previously shown poor or no plant regeneration from callusing primary explants. Callus formation occurred from explants from almost all the lines tested. Significant differences in callus growth were observed among the lines depending on the growth regulator combinations used. Cultural conditions such as type and growth regulator combination, as well as age-dependent competence of the explant tissues, also influenced the frequency of shoot (and/or root) regeneration in Amaranthus species that had been shown difficult to regenerate in the past. The results obtained demonstrate that in Amaranthus the genotype, growth regulator dose and combination, the type and the physiological stage of explant are factors of great importance for in vitro plant regeneration.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Plant cell, tissue and organ culture 45 (1996), S. 67-72 
    ISSN: 1573-5044
    Keywords: Biomass increase ; chromosome count ; growth regulators ; regeneration ; tissue culture ; wormwood
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Callus cultures were initiated from micropropagated Artemisia absinthium plantlets on MS basal medium supplemented with different concentrations of BA, Kn, NAA, IAA and 2,4-d in combination or singly. Supplementing the medium with low doses of both BA in combination with NAA, and Kn in combination with NAA enhanced the growth rate of callus cultures. However, cultures grew slowly following the second subculture and the majority turned brown and died within the next month. Initiation of root and shoot primordia occured directly from leaf explants cultured on 1.81 μM 2,4-d, while adventitious shoot formation from callus was observed occasionally when BA was added to the medium in combination with IAA. Furthermore, medium containing 2.22 μM BA and 2.69 μM NAA stimulated both callus growth and organogenesis on some callus cultures derived from leaves and stems of young stock material. The best results were obtained with leaf explants. Cytological analysis of root meristems revealed that all regenerants were diploid (2n=18), as expected.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-5044
    Keywords: callus histology ; fennel ; growth regulators ; in vitro morphogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Different NAA plus kinetin or BA combinations were tested on Francia Pernod fennel seedlings for callus induction and plant regeneration. Callogenesis from hypocotyls was obtained in all auxin/cytokinin-containing media. The organogenic response was observed especially in presence of NAA plus kinetin. The highest frequency of shoot regeneration was found when the auxin and kinetin were used at a 1:1 ratio. Moreover, a prolonged culture period increased shoot formation. Somatic embryogenesis was tested on several fennel populations. The results gave evidence of the genotypic importance. Two different protocols were used for somatic embryo induction. Using the first protocol among the different fennel genotypes tested, only Francia Pernod showed embryogenic capacity. In this case, from a primary non-embryogenic callus cultured for 12 months in presence of 2,4-D, an embryogenic secondary callus was produced. When transferred to the medium without 2,4-D (agarized or liquid), this gave embryogenic plants in high frequency. As far as the second embryogenic method is concerned, secondary embryogenic callus developed only in the presence of 2,4-D plus kinetin in Francia Pernod genotype. Thereafter, the replacement of those growth regulators by GA3 into the medium greatly increased the somatic embryo development, especially in `Francia Pernod', but also in `Aboca erbe' callus, a population with a very poor embryogenic capacity. In Francia Pernod, the primary and secondary (embryogenic) calli showed different morphological and histological responses, either when the secondary callus was induced by 2,4-D alone or by 2,4-D plus kinetin. Ontogenetic processes leading to somatic embryo formation are described in this context.
    Type of Medium: Electronic Resource
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