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DON Concentrations (don + concentration)
Selected AbstractsCharacterizing nitrogen dynamics, retention and transport in a tropical rainforest stream using an in situ15N additionFRESHWATER BIOLOGY, Issue 1 2002Jeffrey L. Merriam 1.,This study was part of the Lotic Intersite Nitrogen eXperiment (LINX); a series of identical 15NH4 tracer additions to streams throughout North America. 15NH4Cl was added at tracer levels to a Puerto Rican stream for 42 days. Throughout the addition, and for several weeks afterwards, samples were collected to determine the uptake, retention and transformation pathways of nitrogen in the stream. 2.,Ammonium uptake was very rapid. Nitrification was immediate, and was a very significant transformation pathway, accounting for over 50% of total NH4 uptake. The large fraction of NH4 uptake accounted for by nitrification (a process that provides energy to the microbes involved) suggests that energy limitation of net primary production, rather than N limitation, drives N dynamics in this stream. 3.,There was a slightly increased 15N label in dissolved organic nitrogen (DON) the day after the 15NH4 addition was stopped. This DO15N was < 0.02% of DON concentration in the stream water at the time, suggesting that nearly all of the DON found in-stream is allochthonous, or that in-stream DON production is very slow. 4.,Leptophlebiidae and Atya appear to be selectively feeding or selectively assimilating a very highly labelled fraction of the epilithon, as the label found in the consumers became much higher than the label found in the food source. 5.,A large spate (>20-fold increase in discharge) surprisingly removed only 37% of in-stream fine benthic organic matter (FBOM), leaves and epilithon. The fraction that was washed out travelled downstream a long distance (>220 m) or was washed onto the stream banks. 6.,While uptake of 15NH4 was very rapid, retention was low. Quebrada Bisley retained only 17.9% of the added 15N after 42 days of 15N addition. Most of this was in FBOM and epilithon. Turnover rates for these pools were about 3 weeks. The short turnover times of the primary retention pools suggest that long-term retention (>1 month) is minimal, and is probably the result of N incorporation into shrimp biomass, which accounted for < 1% of the added 15N. [source] Fusarium culmorum Infection of Barley Seedlings: Correlation between Aggressiveness and Deoxynivalenol ContentJOURNAL OF PHYTOPATHOLOGY, Issue 6 2002HELLE HESTBJERG Fusarium culmorum is a serious plant pathogen, especially on cereals. The production of deoxynivalenol (DON) by F. culmorum is believed to play a role in pathogenesis. This relationship has been almost exclusively studied in connection with head blight. The present paper reports the first finding of DON in cereal seedlings infected with F. culmorum. A pathogenicity test was performed, including 70 isolates of this pathogen from different sites within northern and central Europe. All isolates caused disease on barley seedlings. For 15 isolates with varying aggressiveness, the DON content in the 19-day-old-barley seedlings was determined. There was a significant correlation between DON concentration and disease index. The aggressiveness of two outlying isolates with very low DON production is discussed. The results indicate that for F. culmorum isolates of the DON chemotype, production of this toxin influences the aggressiveness of the isolates towards barley seedlings. [source] Controls on surface water chemistry in two lake-watersheds in the Adirondack region of New York: differences in nitrogen solute sources and sinksHYDROLOGICAL PROCESSES, Issue 10 2007Mari Ito Abstract The southwestern Adirondack region of New York receives among the highest rates of atmospheric nitrogen (N) deposition in the USA. Atmospheric N deposition to sensitive ecosystems, like the Adirondacks, may increase the acidification of soils through losses of exchangeable nutrient cations, and the acidification of surface waters associated with enhanced mobility of nitrate (NO3,). However, watershed attributes, including surficial terrestrial characteristics, in-lake processing, and geological settings, have been found to complicate the relationships between atmospheric N deposition and N drainage losses. We studied two lake-watersheds in the southwestern Adirondacks, Grass Pond and Constable Pond, which are located in close proximity (,26 km) and receive similarly high N deposition, but have contrasting watershed attributes (e.g. wetland area, geological settings). Since the difference in the influence of N deposition was minimal, we were able to examine both within- and between-watershed influences of land cover, the contribution of glacial till groundwater inputs, and in-lake processes on surface water chemistry with particular emphasis on N solutes and dissolved organic carbon (DOC). Monthly samples at seven inlets and one outlet of each lake were collected from May to October in 1999 and 2000. The concentrations of NO3, were high at the Grass Pond inlets, especially at two inlets, and NO3, was the major N solute at the Grass Pond inlets. The concentrations of likely weathering products (i.e. dissolved Si, Ca2+, Mg2+, Na+) as well as acid neutralizing capacity and pH values, were also particularly high at those two Grass Pond inlets, suggesting a large contribution of groundwater inputs. Dissolved organic N (DON) was the major N solute at the Constable Pond inlets. The higher concentrations of DON and DOC at the Constable Pond inlets were attributed to a large wetland area in the watershed. The DOC/DON ratios were also higher at the Constable Pond inlets, possibly due to a larger proportion of coniferous forest area. Although DON and DOC were strongly related, the stronger relationship of the proportion of wetland area with DOC suggests that additional factors regulate DON. The aggregated representation of watershed physical features (i.e. elevation, watershed area, mean topographic index, hypsometric-analysis index) was not clearly related to the lake N and DOC chemistry. Despite distinctive differences in inlet N chemistry, NO3, and DON concentrations at the outlets of the two lakes were similar. The lower DOC/DON ratios at the lake outlets and at the inlets having upstream ponds suggest the importance of N processing and organic N sources within the lakes. Although an inverse relationship between NO3, and DOC/DON has been suggested to be indicative of a N deposition gradient, the existence of this relationship for sites that receive similar atmospheric N deposition suggest that the relationship between NO3, and the DOC/DON ratio is derived from environmental and physical factors. Our results suggest that, despite similar wet N deposition at the two watershed sites, N solutes entering lakes were strongly affected by hydrology associated with groundwater contribution and the presence of wetlands, whereas N solutes leaving lakes were strongly influenced by in-lake processing. Copyright © 2006 John Wiley & Sons, Ltd. [source] Contribution of dissolved organic nitrogen to N leaching from four German agricultural soilsJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 6 2002Jan Siemens Abstract Dissolved organic nitrogen (DON) substantially contributes to N leaching from forest ecosystems. However, little is known about the role of DON for N leaching from agricultural soils. Therefore, the aim of our study was to quantify the contribution of DON to total N leaching from four agricultural soils. Concentrations and fluxes of DON and mineral N were monitored at two cropped sites (Plaggic Anthrosols) and two fallow plots (Plaggic Anthrosol and Gleyic Podzol) from November 1999 till May 2001 by means of glass suction plates. The experimental sites were located near the city of Münster, NW Germany. Median DON concentrations in 90 cm depth were 2.3 mg l,1 and 2.0 mg l,1 at the cropped sites and 1.6 mg l,1 and 1.3 mg l,1 at the fallow sites. There was only a slight (Anthrosols) or no (Gleyic Podzol) decrease in median DON concentrations with increasing depth. Total N seepage was between 19 kg N ha,1 yr,1 and 46 kg N ha,1 yr,1 at the fallow sites and 16,159 kg N ha,1 yr,1 at the cropped sites. For the fallow plots, DON seepage contributed 10,21,% to the total N flux (4,5 kg DON ha,1 yr,1), at the cropped sites DON seepage was 6,21,% of the total N flux (6,10 kg DON ha,1 yr,1). Thus, even in highly fertilized agricultural soils, DON is a considerable N carrier in seepage that should be considered in detailed soil N budgets. Beitrag von gelöstem organisch gebundenen Stickstoff zur N-Auswaschung aus vier deutschen landwirtschaftlich genutzten Böden Während viele Studien die Bedeutung der Auswaschung von gelöstem organisch gebundenen Stickstoff (DON) für N-Verluste aus Waldökosystemem zeigen, existieren nur wenige Daten zur DON-Auswaschung aus landwirtschaftlich genutzten Böden. Das Ziel unserer Studie war es deshalb, den Beitrag von DON zur Auswaschung von N aus vier landwirtschaftlichen Böden zu quantifizieren. Von November 1999 bis Mai 2001 erfassten wir die Konzentrationen und Flüsse von DON und mineralischem Stickstoff auf zwei bewirtschafteten Flächen (Plaggenesche) und zwei Bracheflächen (Plaggenesch und Gley-Podsol) mit Hilfe von Glassaugplatten. Die Untersuchungsflächen befanden sich nahe Münster/Westfalen. Der Median der DON-Konzentrationen in 90 cm Bodentiefe betrug auf den bewirtschafteten Flächen 2.3 mg l,1 und 2.0 mg l,1, auf den Brachen 1.6 mg l,1 und 1.3 mg l,1. Wir stellten nur eine geringe Abnahme (Plaggenesche) oder keine Abnahme (Gley-Podsol) des Medians der DON-Konzentration mit der Tiefe fest. Die Gesamt-N-Auswaschung lag zwischen 19 kg N ha,1 a,1 und 46 kg N ha,1 a,1 für die Bracheflächen und zwischen 16 kg N ha,1 a,1 und 156 kg N ha,1 a,1 für die bewirtschafteten Flächen. Im Falle der Bracheflächen machte DON 10,21,% (4,5 kg DON ha,1 a,1) der Gesamt-N-Auswaschung aus. Dieser Anteil betrug 6,21,% (6,10 kg DON ha,1 a,1) für die bewirtschafteten Flächen. Auch in intensiv gedüngten landwirtschaftlichen Böden ist die Auswaschung von DON also ein wichtiger Austragspfad für N und sollte deshalb in detaillierten N-Bilanzen berücksichtigt werden. [source] | ||||||||||