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  • 1
    ISSN: 1432-0789
    Keywords: Key words Agroforestry ; Mulch ; Nitrogen fertilizer ; Runoff irrigation ; Sorghum bicolor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  The effects of applying either inorganic fertilizer or leaf mulch of Acacia saligna (Labill.) H.L. Wend. on yields of Sorghum bicolor (L.) were compared with an unfertilized control under the high leaching conditions of runoff irrigation in a dry tropical environment. The N use efficiency and transfer from 15N-labelled (NH4)2SO4 or acacia leaves to the sorghum differed in quantity and quality. Only 6% of the applied mulch N was retrieved in the crop, in contrast to 21% of the fertilizer N. The proportions of N in the crop derived from the fertilizers were small, amounting to 7% and 28%, respectively, in the mineral fertilizer and mulch treatments. However, the application of inorganic fertilizer and mulch significantly increased crop grain yield (P〈0.05 and P〈0.1, respectively), biomass production and foliar N contents (P〈0.05). The inorganic fertilizer improved crop yields to a larger extent than mulching. At the same time, more N was lost by applying (NH4)2 SO4 than leaf mulch: only 37% of the N of applied (NH4)2 SO4 was found in the crop and the soil (0–0.3 m), but 99% of the mulched N. High NO3 – contents in the topsoil of the inorganic fertilized sorghum treatments indicated the risk of N leaching. However, more important may have been gaseous N losses of surface-applied NH4 +. From a nutrient conservation point of view, mulches should be given preferance to inorganic fertilizers under high soil pH and leaching conditions, but larger improvements of crop yields could be achieved with mineral fertilizers.
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  • 2
    ISSN: 1432-2285
    Keywords: Fraxinus excelsior L. ; Compartments ; Nitrate reductase ; Nitrate ; Seasonal variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Nitrate reductase activity (NRA), nitrate content and biomass components of leaflets, leaf stalks, old stem, current-year stem and roots of ash trees (Fraxinus excelsior L.) growing in their natural habitats were investigated. In addition, NRA, total nitrogen and nitrate concentration were analyzed in the leaves and roots of ash trees from four different field sites. The highest NRA per gram biomass and also per total compartment biomass was found in the leaflets, even though root biomass was much higher than total leaflet biomass. The highest nitrate concentrations were found in the leaf stalks. Correlations between nitrate availability in the soil and NRA in leaves were not significant due to high variability of the actual soil nitrate concentrations. The seasonal variation in foliar NRA, nitrate concentration and total nitrogen concentration is much smaller in F. excelsior than reported for herbaceous species and is mainly caused by changes in the actual soil nitrate availability and by senescence of the leaves.
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  • 3
    ISSN: 1432-136X
    Keywords: Neurospora ; Calcium ; cAMP ; Protein phosphorylation ; Circadian rhythm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Pulses of some Ca2+ channel blockers (dantrolene, Co2+, nifedipine) and calmodulin inhibitors (chlorpromazine) lead to medium (maximally 5–9 h) phase shifts of the circadian conidiation rhythm ofNeurospora crassa. Pulses of high Ca2+, or of low Ca2+, a Ca2+ ionophore (A23187) together with Ca2+, and other Ca2+ channel blockers (La3+, diltiazem), however, caused only minor phase shifts. The effect of these substances (A 23187) and of different temperatures on the Ca2+ release from isolated vacuoles was analyzed by using the fluorescent dye Fura-2. A 23187 and higher temperatures increased the release drastically, whereas dantrolene decreased the permeation of Ca2+ (Cornelius et al., 1989). Pulses of 8-PCTP-cAMP, IBMX and of the cAMP antagonist RP-cAMPS, also caused medium (maximally 6–9 h) phase shifts of the conidiation rhythm. The phase response curve of the agonist was almost 180° out of phase with the antagonist PRC. In spite of some variability in the PRCs of these series of experiments all showed maximal shifts during ct 0–12. The variability of the response may be due to circadian changes in the activity of phosphodiesterases: After adding cAMP to mycelial extracts HPLC analysis of cAMP metabolites showed significant differences during a circadian period with a maximum at ct 0. Protein phosphorylation was tested mainly in an in vitro phosphorylation system (with35S-thio γ-ATP). The results showed circadian rhythmic changes predominantly in proteins of 47/48 kDa. Substances and treatments causing phase-shifts of the conidiation rhythm also caused changes in the phosphorylation of these proteins: an increase was observed when Ca2+ or cAMP were added, whereas a decrease occurred upon addition of a calmodulin inhibitor (TFP) or pretreatment of the mycelia with higher (42° C) temperatures. Altogether, the results indicate that Ca2+-calmodulin-dependent and cAMP-dependent processes play an important, but perhaps not essential, role in the clock mechanism ofNeurospora. Ca2+ calmodulin and the phosphorylation state of the 47/48-kDa proteins may have controlling or essential functions for this mechanism.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 63 (1984), S. 136-142 
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary With Rumex obtusifolius L., the influence of some environmental conditions on nitrate uptake and reduction were investigated. Nitrate concentrations of plant material were determined by HPLC, the activity of nitrate reductase by an “in vivo” test. As optimal incubation medium, a buffer containing 0.04 M KNO3; 0.25 M KH2PO4; 1.5% propanol (v/v); pH 8.0 was found. Vacuum infiltration caused an increase of enzyme activity of up to 40%. High nitrate concentrations were found in roots and leaf petioles. Nitrate reductase activity of these organs, however, was low. On the other hand, the highest nitrate reductase activity was observed in leaf laminae, which contained lowest nitrate concentrations. In leaves, nitrate content and nitrate reductase activity exhibited inverse diurnal fluctuations. During darkness, decreasing activities of the enzyme were followed by increasing nitrate concentrations, while during light the contrary was true. In petioles diurnal fluctuations in nitrate content were observed, too. No significant correlations with illumination, however, could be found. Our results prove that Rumex obtusifolius is characterized by an intensive nitrate turnover. Theoretically, internal nitrate content of the plant would be exhausted within a few hours, if a supply via the roots would be excluded.
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  • 5
    ISSN: 1573-5036
    Keywords: atmospheric deposition ; δ15N ; δ34S ; forest decline ; nitrogen ; Picea abies ; stable isotopes ; sulfur
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Concentrations and natural isotope abundance of total sulfur and nitrogen as well as sulfate and nitrate concentrations were measured in needles of different age classes and in soil samples of different horizons from a healthy and a declining Norway spruce (Picea abies (L.) Karst.) forest in the Fichtelgebirge (NE Bavaria, Germany), in order to study the fate of atmospheric depositions of sulfur and nitrogen compounds. The mean δ15N of the needles ranged between −3.7 and −2.1 ‰ and for δ34S a range between −0.4 and +0.9 ‰ was observed. δ34S and sulfur concentrations in the needles of both stands increased continuously with needle age and thus, were closely correlated. The δ15N values of the needles showed an initial decrease followed by an increase with needle age. The healthy stand showed more negative δ15N values in old needles than the declining stand. Nitrogen concentrations decreased with needle age. For soil samples at both sites the mean δ15N and δ34S values increased from −3 ‰ (δ15N) or +0.9 ‰ (δ34S) in the uppermost organic layer to about +4 ‰ (δ15N) or +4.5 ‰ (δ34S) in the mineral soil. This depth-dependent increase in abundance of 15N and 34S was accompanied by a decrease in total nitrogen and sulfur concentrations in the soil. δ15N values and nitrogen concentrations were closely correlated (slope −0.0061 ‰ δ15N per μmol eq N gdw −1), and δ34S values were linearly correlated with sulfur concentrations (slope −0.0576 ‰ δ34S per μmol eq S gdw −1). It follows that in the same soil samples sulfur concentrations were linearly correlated with the nitrogen concentrations (slope 0.0527), and δ34S values were linearly correlated with δ15N values (slope 0.459). A correlation of the sulfur and nitrogen isotope abundances on a Δ basis (which considers the different relative frequencies of 15N and 34S), however, revealed an isotope fractionation that was higher by a factor of 5 for sulfur than for nitrogen (slope 5.292). These correlations indicate a long term synchronous mineralization of organic nitrogen and sulfur compounds in the soil accompanied by element-specific isotope fractionations. Based on different sulfur isotope abundance of the soil (δ34S=0.9 ‰ for total sulfur of the organic layer was assumed to be equivalent to about −1.0 ‰ for soil sulfate) and of the atmospheric SO2 deposition (δ34S=2.0 ‰ at the healthy site and 2.3 ‰ at the declining site) the contribution of atmospheric SO2 to total sulfur of the needles was estimated. This contribution increased from about 20 % in current-year needles to more than 50 % in 3-year-old needles. The proportion of sulfur from atmospheric deposition was equivalent to the age dependent sulfate accumulation in the needles. In contrast to the accumulation of atmospheric sulfur compounds nitrogen compounds from atmospheric deposition were metabolized and were used for growth. The implications of both responses to atmospheric deposition are discussed.
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  • 6
    ISSN: 1573-0867
    Keywords: controls ; grassland ; management ; modelling ; nitrous oxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract There is growing awareness that grassland livestock production systems are major sources of nitrous oxide (N2O). Controlling these emissions requires a thorough understanding of all sources and controlling factors at the farm level. This paper examines the various controlling factors and proposes farm management measures to decrease N2O emissions from intensively managed grassland livestock farming systems. Two types of regulating mechanisms of N2O emissions can be distinguished, i.e. environmental regulators and farm management regulators. Both types of regulators may influence the number and size of N2O sources, and the timing of the emissions. At the field and farm scales, two clusters of environmental regulating factors have been identified, i.e. soil and climate, and three levels of management regulators, i.e. strategic, tactical and operational. Though the understanding of these controls is still incomplete, the available information suggests that there is large scope for diminishing N2O emissions at the farm scale, using strategies that have been identified already. For example, model calculations indicate that it may be possible to decrease total N2O emissions from intensively managed dairy farms in The Netherlands in the short term from a mean of about 19 to about 13 kg N per ha per year by more effective nutrient management, whilst maintaining productivity. There is scope for a further reduction to a level of about 6 kg N per ha per year. Advisory tools for controlling N2O emissions have to be developed for all three management levels, i.e. strategic, tactical and operational, to be able to effectively implement emission reduction options and strategies in practice. Some strategies and best management practices to decrease N2O emissions from grassland livestock farming systems are suggested.
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  • 7
    ISSN: 1573-5036
    Keywords: acid irrigation ; liming ; nitrate leaching ; nitrate reductase ; Oxalis acetosella ; Picea abies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Nitrate reductase activities (NRA) and nitrate concentration per unit biomass in Picea abies (L.) Karst. roots from four different soil horizons and in leaves and roots of the frequent field-layer species Oxalis acetosella L. were measured on six different irrigation and liming treatments within the Höglwald project, S-Bavaria, Germany. Liming increased and acid irrigation reduced soil nitrate availability when compared to control plots. Nitrate assimilation capacities of the respective plant compartments per unit of soil volume or ground area were calculated from the NRA per unit of biomass and from the biomass distribution on the various treatments. Mean NRA per unit of biomass in Picea abies roots ranged between 0.23 and 0.09 μmol NO 2 - g-1 d.w. h-1 without significant effects of soil horizon or treatment. Limed and non-limed treatments showed for Picea different root distributions within the soil profile, but root biomass per unit of ground area (295 to 220 g d.w. m-2) was not affected by the various treatments. Thus, nitrate assimilation capacity of Picea roots per unit of ground area ranged between 19.5 and 11.4 μmol NO 2 - m-2 h-1 without major treatment effects. In laminae of Oxalis acetosella mean NRA per unit of biomass ranged between 2.91 and 0.27 μmol NO 2 - g-1 d.w. h-1 and, in contrast to Picea abies, treatment effects were found with NRA on limed plots increased and on acid irrigated plots reduced when compared to control plots. Mean leaf biomass of Oxalis per unit of ground area ranged between 9.57 and 0.66 g d.w. m-2 and responded in a similar manner to the various treatments. Thus, for the Oxalis leaf NRA per unit of ground area (27.85 to 0.18 μmol NO2 m-2 h-1) a cumulative response to the variations in nitrate availability was found. The different responses of Picea abies and Oxalis acetosella to changes in soil nitrate availability are discussed with respect to their suitability to prevent soil nitrate leaching.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 63 (1984), S. 380-385 
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The aim of this work was to investigate the effect of nitrogen starvation and subsequent fentilization with nitrate or ammonium on nitrate content and nitrate reductase activity of Rumex obtusifolius L. under natural conditions. When plants were transplanted to nitrate-poor media, endogenous nitrate was reduced within a few days. In parallel, nitrage reductase activities dropped to about 25% of the initial values. As a consequence of nitrate fertilization (1; 10 or 100 mmol KNO3/l substrate), endogenous nitrate content of the plant abruptly increased within one day. In extreme cases, nitrate concentrations of up to 10% of plant dry weight could be observed without being lethal. High external nitrate concentrations caused an inhibition of nitrate reductase within the leaves, while low external concentrations provoked an increase in the enzyme activity of about 450% within one day. Ammonium fertilization (5 mmol (NH4)2SO4/l substrate) also caused an increase in nitrate reductase activity and nitrate content within leaf blades. This observation indicates a rapid nitrification of ammonium in the substrate. When plants were fertilized with ammonium plus nitrate (2.5 mmol (NH4)2SO4+ 5 mmol KNO3/l substrate), an extremely high and long term increase in nitrate reduction could be observed. Due to an intensive enzymatic nitrate turnover, the nitrate content of leaf blades then remained relatively low. Our observations do not point to an inhibition of nitrate reductase activity in leaves of Rumex obtusifolius by ammonium. Despite temporarily high endogenous nitrate concentrations, Rumex obtusifolius may not be termed as a “nitrate storage” plant, since the accumulation of nitrate is a short term process only.
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  • 9
    ISSN: 1432-1939
    Keywords: Nitrogen use efficiency ; C3 grasses ; C4 grasses ; Biomass production ; Competition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two C3 grasses (Hordeum vulgare L., Avena sativa L.) and two C4 grasses (Panicum miliaceum L., Panicum crus-galli L.) were cultivated in standard soil in the open air in pure cultures and in various mixed cultures at low and high nitrogen fertilization levels. After three months the dry weight, length and nitrogen content of the aboveground and below-ground parts of the plants and the shoot/root ratios were determined. Hordeum vulgare was the most successful species irrespective of the nitrogen fertilization level, and also exhibited in most cases the highest nitrogen concentrations. Panicum miliaceum, on the other hand, was the species least able to compete. The production of biomass was reduced in cultures growing under nitrogen starvation conditions, this phenomenon being more pronounced with respect to the C4 than to the C3 species. The decrease in the production of biomass at low N conditions was most drastic with Panicum crus-galli, the species with the lowest nitrogen content and thus assumed to be best adapted to nitrogen starvation conditions. In cultures growing at low nitrogen fertilization levels the shoot/root ratios of all species.shifted in favour of an increasing root proportion. The extent of this shift, however, differed from species to species.
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  • 10
    ISSN: 1432-1939
    Keywords: Nitrogen use efficiency ; C3 plant ; C4 plant ; Biomass production ; Nitrate metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Pure and mixed cultures of the dicotyledons Atriplex hortensis L. (C3 plant) and Amaranthus retroflexus L. (C4 plant) were maintained under open air conditions in standard soil at low and high nitrogen supply levels. A comparison of shoot dry weight and shoot length in the various series shows that the growth of the aboveground parts of both species was severely reduced under low N conditions. In both pure and mixed cultures the differences resulting from low N vs. high N conditions was less pronounced with Atriplex (C3 plant) than with Amaranthus (C4 plant). The root dry weight of the two species was not reduced so much under low N conditions as was the shoot dry weight. The low N plants were found to contain a larger proportion of their biomass in the roots than did the high N plants. In general the root proportion of Atriplex was greater than that of Amaranthus. The contents of organic nitrogen and nitrate and the nitrate reductase activity (NRA) per g dry weight of both species decreased continually throughout the experiments. With the exception of young plants, the low N plants always had tower contents of organic nitrogen and nitrate and nitrate reductase activities than did the high N plants. The highest values of NRA were measured in the leaf laminae. The eaves also exhibited the highest concentrations of organic nitrogen. The highest nitrate concentrations, however, were observed in the shoot axis, and in most cases the lowest nitrate values were found in the laminae. At the end of ne growing season this pattern was found to have been reversed with Atriplex, but not with Amaranthus. Thus Atriplex was able to maintain a higher NRA in the laminae than Amaranthus under low N conditions. The transpiration per leaf area of the C4 plant Amaranthus during the course of a day was substantially lower than that of the C3 plant Atriplex. There were no significant differences in transpiration between the low N and high N series of Amaranthus. The low N plants of Atriplex, however, clearly showed in most cases higher transpiration rates than the corresponding high N plants. These different transpiration rates of the high N and the low N Atriplex plants were also reflected in a distinct 13C discrimination. The sum of these results points to the conclusion that the C3 plant Atriplex hortensis can maintain a better internal inorganic nitrogen supply than the C4 plant Amaranthus retroflexus under low N conditions and an ample water supply, due to the larger root proportion and the more pronounced and flexible transpiration of the C3 plant.
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